geomatics & vocabulary -...
TRANSCRIPT
Biuro Projektu al. Tysiąclecia Państwa Polskiego 7, 25-314 Kielce
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Projekt ,,Politechnika Świętokrzyska – uczelnia na miarę XXI w.’’ Program Operacyjny Kapitał Ludzki Priorytet IV Działanie 4.1, Poddziałanie 4.1.1
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MATERIAŁY DYDAKTYCZNE DO PRZEDMIOTU
GEOMATICS & VOCABULARY
Wykłady 15 h
Wydział Inżynierii Środowiska, Geomatyki i Energetyki
Opracował - Ryszard Florek Paszkowski
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Projekt ,,Politechnika Świętokrzyska – uczelnia na miarę XXI w.’’ Program Operacyjny Kapitał Ludzki Priorytet IV Działanie 4.1, Poddziałanie 4.1.1
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CONTENTS
1. APPLICATION OF A FILM CAMERA TO HIGH VARIABILITY DEFLECTION
PHOTOGRAMMETRIC MEASUREMENTS OF LIGHTING METALLIC TOWERS. 3
1.1. Introduction. 3
1.2. The object of measurements 3
1.3. Photogrammetric method of tower movements using a film camera. 5
1.4. Film tape elaboration by projection and analytical method. 8
1.5. Trajectory diagrams of tower vibrations and axial torsions of the towers. 12
1.6. Final conclusions. 12
2. PHOTOGRAMMETRIC MEASUREMENTS AND DOCUMENTATION OF A SEA –VESSEL
HULL FOR INSURANCE PURPOSES. 16
2.1. The need to measure vessels. 16
2.2. The Aubacora project – a practical stereo-photogrammetric survey of a fishing vessel. 22
2.3. Discussion and analysis. 26
2.4. Conclusions and recommendations 27
3. THEMATIC MAPPING AND PHOTOGRAMMETRIC MEASUREMENTS OF JOHANNESBURG
AREA, FROM SATELLITE MK-4 CAMERA PHOTOGRAPHS. 30
3.1. Photography for space monitoring systems 30
3.2. MK-4 space photographic camera. 31
3.3. Control and restitiution of the 3D model. 31
3.4. Corrections applied to stereo model. 32
3.5. Conclusions. 33
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1. APPLICATION OF A FILM CAMERA TO HIGH-VARIABILITY
DEFLECTION PHOTOGRAMMETRIC MEASUREMENTS
OF LIGHTING METALLIC TOWERS
The chapter presents a method and results of photogrammetric measurements of high-variability
deflections and axial torsions of 58 m highlighting metallic towers. Film registration was taken with a
16 mm film camera, placed on the tower foundation plate in nearly vertical, constant camera
orientation. The film-tape was measured by projection-graphical method using special review table and by analytical method using a stereo-comparator for measurements of image coordinates and a
computer in transformation to ground coordinates. The trajectories of the tower vibrations were
obtained and axial torsions were computed. The results of the measurements confirmed the experts' thesis that the tower vibrations were caused by the Karman spins. The results of test experiments
referring to the accuracy of the presented method are also reported.
1.1. INTRODUCTION
In the area of dislocation and deformation measurements, the investigations of the dynamic processes, such as high-variability dislocations and deformations of buildings and engineering
constructions, are very important. The object of these investigations is: the control and indication of
danger for buildings showing phenomena caused by excessive dislocation and deformation. The
results of measurements permit to compile suggestions about the building and the related problems. In geomatic practice we have many surveying methods, but for measurements of dynamic
phenomena the photogrammetric methods are especially suitable, particularly those where a speed
film camera is used. These methods are characterized by nearly zero time inertia of measurement and also by the fact that the camera does not touch the measured object because it can be moved away
from the range of influences which can disturb the measurements.
The effect of measurement of dynamic process is most frequently a series of successive positions of the measured object and its state as a deformed body in a given coordinate system and time
function. Comparing the results of measurements taken in time T1 and T2, the trajectory of the process
in time AT= T2 – T1 can be inferred and the changes in geometrical dimensions of the object
measured can be found. In this case, the computations of dislocation and deformation of the measured object in time AT must be performed.
1.2. THE OBJECT OF MEASUREMENTS
Four lighting metallic towers, 58 m high, situated on the sports stadium GTS Vistula in Cracow -
fig. 1.1 - were measured. According to ,,Technical report", after the construction of the towers had been completed, their vibrations of high amplitudes and low frequencies were observed in specific
atmospheric conditions. The vibrations arise when the wind is blowing perpendicularly to the
searchlight part of the tower. These vibrations are transverse, in the plane perpendicular to the wind direction. To be more precise, in the plane perpendicular to the wind direction, the maximum
deflection of the main part of the tower is observed. Since such vibrations can be dangerous for the
tower construction, provisional guy ropes were set up on the four towers on the searchlight level.
According to the experts, the phenomena of wind resonance appear here in connection with Karman's spins, when constant speed air stream flows around the cylindrical rod. High amplitudes of
the construction vibrations cause: a) changes of strength type and increase in stress, which can reach
the limit of admissible values, b) changes of fatiguetesting type of the material structure, which can lead to unexpected fractures without earlier plastic signals. The construction plan of the tower was
designed according to the obligatory contemporary (1967) regulations without any faults. The
limitation of tower vibrations will be realized by:
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1) closing the open part of the tower bowl,
2) setting up special spiral wings to prevent Karman's spins,
3) when searchlights are mounted, the aerodynamic situation will be better because they disturb
the laminar stream of wind.
Fig. 1.1. Lighting tower before searchlights were installed.
The measurements of high-variability movements of the towers had two aims:
a) control of the tower behavior, i.e. signaling of unprofitable phenomena and ascertaining the degree
of efficiency of the protection means,
b) cognitive aim, since the results of measurements will permit to formulate scientific conclusions
with regard to this type of constructions and, consequently, to introduce appropriate
recommendations to building regulations.
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Fig. 1.2. Lighting tower with searchlights.
1.3. PHOTOGRAMMETRIC METHOD OF MEASUREMENTS OF TOWER
MOVEMENTS USING A FILM CAMERA
1.3.1. Adaptation of a film camera
From surveying point of view, a problem of measurements of high-variability dislocations and
dynamic deformations arises. Geomatic methods used for determination of high building deflections
could not be applied because of a big time inertia, both of geomatic instruments and the operator, in
relation to the speed of vibrations and axial torsions of towers.
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A photogrammetric method based on a film camera was devised. It used the film tape for registration. A 16 mm film camera Krasnogorsk was adapted for the measurements - fig. 1.3. The
objective Telemegor 1:5,5/250 mm with the focal length 12,5 times longer than the standard one was
used with the camera. The film in the camera is step transported, frame by frame, by means of a mechanical holder. At the moment of exposition of each frame, the film is motionless and pressed to
the film channel. The tripod head permits to rotate the camera in horizontal plane and tilt it by an angle
over 90°.
Fig. 1.3. Camera with Telemegor lens 1:5,5/250 mm
1.3.2. Distribution of target points on the towers
The shape and dimensions of the target points were selected with a view to obtaining the best
readability on the film. It was found that the most advantageous were target marks with a hole, which
against the sky gave the infallible identification on the film - fig. 1.4. The targets were made of 2 mm
sheet steel. On each tower, the system of targeted marks was installed (towers 1,2 and 3 have three and
tower 4, four target marks). The target points were fastened to the tower trunk at the height of 56 m from the foundations. Inside the tower, a steel ladder is installed, which allows to reach the top of the
tower. All the distances between target points were measured with a steel measuring tape. Extreme
points were located on the average at a distance of 1500 mm. When the towers were equipped with sets of searchlights, they covered the targeted marks - fig. 1.5. Since then, the edges of searchlight-
boxes have been used for observations. The dimensions of these boxes were measured directly and the
edges of the highest (55 m) and lowest (43 m) boxes on each tower were assumed for observation.
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Fig. 1.4. Target mark.
Fig. 1.5. Searchlight on the tower.
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1.3.3. Film registration
The camera station was situated on the foundation plate of the tower - fig. 1.6. Film registration
was taken when the lens axis was nearly vertical and at constant orientation.
Fig. 1.6. Camera on the station.
A speed of wind was measured by the AJ/49 anemometer during whole recording time. Figs 1.7 and 1.8 show enlarged photographs of 16 mm film sections taken with a film camera. Fig. 1.7 presents
the measurements of the fourth tower, where we can see a set of four target points on the level of 56 m
denoted with numbers 1 , 2 , 3 , 4 and also two additional points on the level of 42 m, denoted with
numbers 5 and 6. Fig. 1.8 shows the upper part of the third tower and the numbers 5, 6, 7 and 8 indicate the edges of searchlight boxes assumed as observation points.
1.4. FILM TAPE ELABORATION BY PROJECTION AND ANALYTICAL METHOD.
A special Fenix-Synchro review-table shown on fig. 1.9 and projection-graphical method were
used for preliminary elaboration of the film-tape. This method is based on the projection of individual film frames on the screen situated in such a way that the successive positions of the observed points
can be marked. At the beginning, a sheet of paper with the position of targeted points for the given
tower (in a given scale) is attached to the screen. Then the screen must be set to the position at which
plotted and projected targeted points are adjusted. The screen is kept in this position, and the location of fiducial marks of image plane is drawn on a new sheet of paper. Now each film-frame is projected
and adjusted to the fiducial marks and then the position of targeted points is plotted on the screen. As a
result, a trajectory of the vibration process is obtained. Depending on the density of trajectory points, each film-frame or every, fifth or tenth film frame can be elaborated.
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Fig. 1.7. The enlarged photo of the tower with 6 marks located on levels 56 m and 42 m
The scale 1:10 was chosen, i.e. 1 mm in screen plane corresponded to 10 mm in the plane of
targeted points on the tower. Vibrations of the foundation caused by high-variability deflections of the
tower-body do not affect the stability of the camera orientation. Depending on requirements and
atmospheric conditions, the velocity of screening was: 48, 32 or 24 film-frames per second. ORWO UP 15 and UP 32 films were used. Telemegor 1:5,5/250 mm lens has a satisfactory field of view for
registration of trajectory deflection and gives satisfactorily large scale image.
Simultaneously with screening, the speed of the wind was measured, using AJ-49 anemometer. The station of wind speed V measurement was placed at the central point of sports stadium and the
anemometer was set on a two meter stick. The readings from the anemometer were taken every 15
second and for each minute the average value Vav was computed. The wind speed was measured
several minutes before screening registration and during the registration.
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Fig. 1.8. The enlarged photo of the tower with searchlights boxes.
In one case the wind speed measurements were performed simultaneously at two points: one anemometer was placed as usual at the central point of the sports stadium and the other on the tower,
43 m above the ground level and was set on an arm. The average wind speed on the tower (Vm.T),
taken from 10 minute period, was 2,2m/sec higher than the average on the stadium level (Vav.s). This
value 2,2 m/sec, can be approximately regarded as the local constant of the decrease of wind speed on the ground level in comparison with the speed on the highest level of the tower. The information about
the wind speed was also taken from the State Forecast Office (PIHM) but because of the distance of a
dozen or so kilometers, it had only approximate meaning. To evaluate more precisely the dynamic phenomena of vibrations, the measurements of wind speed should be taken along the tower-body.
The accuracy is characterized by the standard error M0 = 2 cm of the position of trajectory point in
the plane of targeted points.
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The projection-graphical method permits a quick elaboration of a long film-tape. This, in turn makes it possible to select the film and choose the more interesting sections for more accurate but also
more labor consuming analytical process.
Fig. 1.9. Synchro-Fenix review table
The analytical method consists of two stages:
a) the measurements of the image coordinates,
b) computing transformation of the coordinates. The measurements of image coordinates of targeted points and four fiducial marks imaged in the
film channel were made with Zeiss 1818 stereocomparator. Image coordinates u, v were measured using parallax screws p(v) and g(u) — fig. 1.10. Additional telescope allowed to magnify the image to
96 times.
Then, a transformation from the system u, v to ground system x, y was performed. The u, v system is connected with the right stereocomparator carriage (p, q). The axes of x\ y system, on the other
hand, are perpendicular to the optical axis of the camera objective on the camera station, the x, y —
plane being situated on the level of the tower targeted points. Conformal transformation of the first degree was used. Computations were performed using a computer. For computation of transformation
coefficients only two control points are required. When more than two control points were available,
computations of transformations coefficients were made with adjustment. For each film-frame
transformation-coefficients and then x and y coordinates were computed. The standard error of the position of the trajectory point in the plane of targeted points is equal to M0 = 2 mm = 0,009 mm in the
image plane.
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Fig. 1.10. Coordinates measurements with Zeiss 1818 stereocomparator.
1.5. TRAJECTORY DIAGRAMS OF TOWER VIBRATIONS AND AXIAL TORSIONS OF
THE TOWERS
Basing on x, y coordinates, trajectory diagrams of high-variability movements of the towers were
made. On diagrams, the direction and velocity of the wind are shown. Fig. 1.11 illustrates three vibration trajectories of tower No. 4 when provisional guy ropes were set. Fig. 1.12 (tower No. 3)
shows two diagrams of trajectories on two levels: 43 m -inside trajectory and 55 m — outside
trajectory, which were recorded at the same time. To illustrate the regularity of trajectory vibration parameters (fig. 1.13), a diagram of three successive trajectories was drawn. The time interval of
trajectory points for all diagram is 0.125 sec.
Computations of axial torsions were made for vibrations with higher amplitudes of deflections. The maximum values of axial torsions were up to 1 degree 56 minute angle.
1.6. FINAL CONCLUSIONS
1) The measurements confirmed the experts' thesis that vibrations of the towers were caused by
Karman's spins. 2) The presented method of photogrammetric measurement of tower movements permits a
simultaneous recording of movements on several tower levels and a calculation of the tower axial torsions.
3) This method may find wide application in the investigations of high-variability processes in engineering measurements
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Fig. 1.11. Trajectories of tower vibrations on the level of 56 m with provisional guy ropes.
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Fig. 1.12. Trajectories without guy ropes.
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Fig. 1.13. Three successive trajectories on the level of 55 m.
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2. PHOTOGRAMMETRIC MEASUREMENTS
AND DOCUMENTATION OF A SEA-VESSEL HULL
FOR INSURANCE PURPOSES
This chapter investigates the usefulness and applicability of close-range photogrammetry to the
marine industry, not only from a technical point of view, but also regarding classification, registration and insurance aspects as well. It is suggested that close-range photogrammetry, performed during
routine marine surveys of a vessel hull, provides valuable technical information which is essential to
the marine underwriter. In particular, the use of stereo-photogrammetric documentation methods which provide reliable stereoscopic three-dimensional interpretation and measurements, is strongly
suggested to marine underwriters.
The shipping industry, the world over-relies on marine insurance for peace of mind. While safe
passage of goods or people can never be fully guaranteed, the underwriter pledges to cover the
specified risks involved, and thereby minimizes the losses incurred in the event of a marine accident.
Research shows that sound technical evaluations of vessels are desired by underwriters, as a basis upon which to make sound actuarial decisions. How else should an underwriter compute the risk
associated with insuring a vessel, other than with reliable and verifiable documentation?
A practical photogrammetric survey, of a fishing vessel hull has been carried out at Cape Town’s
Waterfront Synchro-lift, using metric and non-metric cameras. Results indicate that stereo-
photogrammetric documentation is able to record vessel details such as rust patches, weld lines, etc., to 5mm accuracy, with respect to the vessel itself. Stereo-photogrammetric measurements were
processed to digital, three-dimensional co-ordinate format. Provided that one has the appropriate
software, any form of data visualization is then possible as surface models, plan views or cross-sections.
Stereo-photogrammetric documentation is found to be highly appropriate for supplying the marine
underwriter with sound technical information on vessel hulls by providing: visual, remotely sensed, permanent, storage-efficient, and archival information which is independently verifiable.
2.1. THE NEED TO MEASURE VESSELS
Firstly, let us answer the question - Why is there a need to measure and document the
characteristics of a given vessel? - from global and local perspectives. The maritime community's desire to define, measure, and record the size of a vessel, particularly its internal cargo-carrying
capacity, has been apparent as long as there have been merchant ships engaged in international trade
[Surveyor 1994 Dec.]. Systems of 'tonnage' have been particularly important, records of which date
back long before the Christian era. Such systems have tried to standardize the quantifying of a vessel's internal volume, i.e. its net tonnage, in order to estimate that vessel's earning capability (cargo). Other
systems determine gross tonnage, used to calculate things such as port duties, premiums with
underwriting bodies, and dock dues [Surveyor 1993 Dec.; p.30].
Most maritime countries have legislation designed to regulate shipping activities, with the overall
focus being on safety at sea. In South Africa, the Merchant Shipping Act, No. 57 of 1951, fulfils this
purpose. The Act requires every vessel of 25 or more gross tons, owned or operated by a South African citizen or concern, to have its particulars entered in an official register [Ch.2, Sec. 10 & 13].
Registration at a gazette “Port of Registry” must be preceded by a marine survey, so as to ascertain the
tonnage of the vessel [Ch.2 Sec.16]. Details of the vessel's dimensions must also accompany registration [Ch.2 Sec.20].
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Further to these requirements, any ship registered in RSA which is greater than or equal to 14m in
length, and is not solely engaged in fishing or yachting, must have a Load Line Certificate (LLC).
Such a certificate attests that the 'load line ship' has been surveyed, and that the vessel's hull has been marked to reflect the maximum depths to which that vessel may be loaded for various sea conditions.
The salient point here is that a load line ship must be thoroughly surveyed prior to her being put into
service, and subsequently at intervals not exceeding five years [Article 14 a & b]. This brief outline of the areas where marine surveys are performed is intended to emphasize the market demand for such
work.
2.1.1. MARINE INSURANCE
It should be apparent to the reader that the motivation behind the conventions and legislation, and
therefore the marine surveys, is the safeguarding of lives, interests, and capital assets in the shipping industry. However, since no ship's passage is guaranteably without incident or mishap, the 'parties to a
marine adventure' have found it necessary to protect themselves from unfortunate losses. The role of
the marine underwriter is thus created. Marine insurance is designed to minimize the financial
damages sustained in a maritime accident, it is not however compulsory. In return for relative peace of mind, a vessel operator or owner will pay an insurance company a premium. The cost of insurance
depends directly on the risk that the insurance company associates with the policyholder's vessel.
There are two kinds of marine insurance: property insurance and liability insurance. The ship-owner or operator's liability insurance is essentially protection and indemnity (P&I)
coverage. Marine property insurance concerns the insurance of cargo and hulls, the latter being of
particular relevance to this project. Hull insurance covers all the vessel's equipment and structures, as well as liability for damage to another vessel, in the event of collision. Nick Blenkly, in the
September 1991 issue of SURVEYOR [p.22], reports that there has of late been an increase in the
number of large insurance claim settlements. Consequently, insurance market 'capacity' has shrunk; it
is a simple matter of economics that ship-owners are now having to pay substantially higher premiums. However, Blenkly goes on to add that there is a positive aspect to a pressurized marine
insurance market. He makes the significant suggestion, that it would be easier for insurers to guarantee
peace of mind if they could place more emphasis on sound, technical appraisals of the risks they are covering. To summarize: "... in such a market, the ship-owner with a good insurance record is less
likely, in the long term, to find himself subsidizing less careful operators". Marine insurers specialize
in risk assessment, not in technical investigations. Consequently, if a ship-owner is to enjoy discounted insurance premiums resulting from his vessel being of sound construction and well
maintained, he requires a more comprehensive marine survey than that afforded by adhering to
minimum legislation.
Geoff Broad, from the Technical Services Division of insurance company First Bowring and Associates in Johannesburg, has explained [BROAD, 1994], that "there has been a major push by
underwriters in the last few years to 'clean up' the seas of the sort of vessels that have been seen
around the Cape recently... They [underwriters] have utilized the [marine] surveyors of Classification Societies to do this, and annual surveys are an underwriting requisite of oil tankers over a certain age,
for instance. Any method that saves costs and is easier to perform for this increasing volume of
surveys could therefore be very beneficial.".
2.1.2. CLASSIFICATION SOCIETIES
Classification Societies are non-governmental companies offering a wide range of inspection and validation services to ship owners and operators alike. At present there are 42 Classification Societies
operating world-wide [STD-BUL, 1994]. In the normal course of events on a deep sea vessel,
insurance will not be considered unless the vessel is in possession of full, current Classification
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Society Certificates of Class for Hull, Machinery, Automation, and Special Features… [MATHESON, 1994]. It should be noted that classification, as such, has no legal status, although a ship not certified
as ‘in class’ by a reputable Society is unlikely to obtain insurance or employment [GUY, 1989; p.105].
Right from their origins, the primary function of Classification Societies was to provide marine underwriters with information describing the actual condition of vessels insured [B.V., 1989; 7].
Fig. 2.1. Marine Casualties.
Nowadays, the vast majority of shipping communities firmly support the concept of classed ships; merchant vessels designed, built, and maintained to the high technical standards established and
administered by Classification Societies [B.V., 1989; p.7]. Moreover, a very commonplace proviso in
marine insurance contracts is a clause which warrants that the vessel insured be kept ‘in class’ throughout her period of entry on the underwriter’s books. Apart from classification, the technical
services offered by Classification Societies may include, for instance, naval architecture,
hydrodynamics, structural analysis, and vibration analysis [B.V., 1989; p.29].
2.1.3. SHIP CONSTRUCTION, ALTERATION, AND DIMENSIONAL CONTROL
Prior to exploring the topic of marine surveys it is necessary to understand something about the construction of vessels themselves. The curves delineating a vessel's hull are generally not
mathematical expressions, and it is therefore necessary to have a 'lines plan' which will depict (in as
detailed a manner as possible) this surface of the ship [TAYLOR, 1987; p.33]. The lines plan consists of three drawings which show three sets of sections [TAYLOR, 1987; p.35]. Each of three mutually
orthogonal planes gives a different plan: body plan (planes perpendicular to the vessel centerline);
waterlines or level lines (horizontal planes parallel to the vessel base); and sheer profile or buttocks
(vertical planes parallel to the vessel centerline). Many other detail plans are required during construction, but these will all be based upon the 'principal dimensions' of length, depth, and breadth
[TAYLOR, 1987; p.26].
Ships are usually built into jigs, which are preassembled to represent the design dimensions as best
as possible. The individual metal sheets are then bent, rolled, or beaten to conform to the jig
structures; the vessel often goes 'out of design' at this stage [TAGGART, 1980]. Methods of
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dimensional control, and associated tolerances, are influenced by the following assembly and fabrication considerations [TAGGART, 1980; p.629]:
structural acceptability - in accordance with regulations of a particular agency;
operational acceptability - to satisfy the client's special requirements; fabrication requirements of the shipyard - emphasis on cost-effectiveness.
It would appear that while standard tolerances for construction are desirable, what is more relevant to
the shipbuilder are tolerance limits. Such limits should come from Classification Societies, based on input from research, industry, and service experience [TAGGART, 1980; p.630]. The matter of
acceptable tolerances depends largely on the stress condition of the fabrication material, the location in
the ship, and the judgment of the marine surveyor.
Dimensional control methods for fabrication and assembly are essentially the same as those used in
subsequent marine surveys, as well as in the alteration or modernization of vessels. These include the
use of calibrated steel tapes, set-squares or 3-4-5 tape triangulation, while level planes are determined using elementary hydrostatic levelling - the water tube method [TAGGART, 1980; p.630]. Piano wire
is used for aligning over short distances, whereas theodolites and lasers are used for aligning major
components such as keel blocks and shafts.
Close-range photogrammetry in the ship building industry has been successfully used in the United States [KENEFICK, 1977] as well as European countries, for point-by-point assembly control.
2.1.4. MARINE SURVEYS
The marine survey is an inspection, recording and measurement process relating to a ship. Marine
surveyors do not normally require any special marine qualification, although the majority will possess a marine background [GUY, 1989; p.2]. The purpose of any statutory or class survey is to be able to
provide the ship with a document certifying its compliance with certain standards. In many cases the
Classification Societies have assumed the role of government agencies, carrying out the requisite
surveys and issuing international certification on behalf of the administration [GUY, 1989; p.105]. If a vessel is not classed, she will nonetheless have to satisfy minimum standards of strength, and will
undergo similar surveys to a classed vessel. These classification surveys are listed below [KEMP &
YOUNG, 1989; p.4] : Annual Survey;
Docking Survey - every 12 to 24 months;
Special Surveys - every four years, increasingly severe with age of vessel. In addition, any time there is an insurance claim against the vessel, a survey of the relevant aspects
of that vessel will take place [TAGGART, 1980]. All hull deformations and distortions, systematic or
otherwise, inherent or unnatural, have implications for any measuring or recording methodologies
used in a survey of a ship. Measurements in the field are made using steel tapes and battens in an offset method. The reliability of any measurement in a marine survey thus depends on the past history
of the plate or assembly involved in that measurement.
2.1.5. SUPERIOR APPLICABILITY OF STEREO-PHOTOGRAMMETRIC SURVEYS
A documentation survey is a general survey of a structure, the final application of which are not
exactly known a priori, although the surveyor has a good understanding of the scope of his client's future requirements. The writers believe that vessel-hull documentation, for non-specific insurance
purposes, is best performed using stereo-photogrammetric methods, for the following reasons
concerning: 1) Cost,
2) Time,
3) Legal and Archival Factors of Stereo-Photogrammetric Surveys.
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Perhaps the most considerable advantage of stereo-photogrammetric documentation surveys is the ability to explore the subject of photography in three dimensions. This aspect of stereo-interpretation
plays a key role in these surveys and allows the observer to discern between object features which
might well be indistinct on a single plane photograph while measured monoscopically.
If a stereo-photogrammetric survey of a vessel hull is carried out while a vessel is in dry-dock
condition, the work may be performed in the background, so to speak, with minimal disruption to routine operations. Such conditions enable the docking period to be more cost-effectively used.
Photography in itself is a rapid process. The primary limitation on speed of operation is the bulkiness -
or otherwise - of the camera equipment used, and the size of the vessel to be photographed.
Insofar as a comprehensive stereo-photographic record of a hull permits the entire hull to be
explored in three dimensions, the greatest benefit is obtained if that survey forms part of a series of
surveys performed over the course of time. Deformation - depending on the level of precision required - may be detected and monitored. Photogrammetry can also be useful for recording and
measurement of dynamic deformations of a vessel hull during a launching [FLOREK, 1975, p.88-94].
Features or parts of the vessel hull (or even the superstructure), which find themselves the subject of a legal/insurance dispute between two or more parties, can be visually scrutinized in a fully
restituted three dimensional environment. Furthermore, should the need arise to quantify damage,
measurements can performed to a degree of precision surpassing that of traditional marine survey measurements. The photographs comprising a photogrammetric survey therefore represent compact
and efficient databases, the contents of any part of which may be independently examined by objective
experts in the field of photogrammetry.
2.1.6. INSTRUMENTATION AND METHODOLOGY FOR STEREO-SURVEYS
The primary categories of cameras encountered in close-range photogrammetry are metric and non-metric photographic and digital CCD (Charge Coupled Device) cameras. Metric photographic
cameras usually have the following features:
1) precisely designed and calibrated; 2) known, stable interior orientation;
3) often fixed focus;
4) contain fiducial marks or reference grid for inner orientation purposes; 5) contain film flattening devices or allow glass plates;
6) relatively expensive.
An example of such camera is the Zeiss UMK 10/1318, used in this practical test project described
presently. Fitted with four fiducial marks, and taking single cut-film cartridges, this camera is currently priced at USD 20k [HON, 1994].
Non-metric cameras are often termed 'amateur' cameras, and usually have the following features:
a) usually hand-held; b) unstable interior orientation;
c) non-rigid construction - variable focus;
d) no fiducial marks;
e) lens design often sacrifices geometry for image resolution; f) relatively inexpensive and widely available.
A Mamiya C330, costing approximately in the region of USD 4k [HON, 1994], was also made use of
in the test survey. This camera can be equipped with a reference grid glass plate for additional cost of USD 500.
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Fig. 2.2. Mamiya C330 and Zeiss UMK 10/1318 cameras.
The latest sample Kodak, Nikon, Canon CCD cameras, available on commercial market, represent following features:
one image is composed of about 24 megapixels of data;
storage capacity on memory cards – depends on card capacity – up to 4k photos;
28mm CCD lens acting as 70mm (regarding bundle angle); battery operated;
full self-calibration necessary to estimate image geometry and stability;
CCD camera costs approximately USD 5k. A one pixel resolution of this camera equipped with Nikon 28mm lens is approximately 1 mm at 10m camera-to-subject distance, which is about 10 times
less than for the UMK using glass plates. This equates approximately with 10 times decrease in
resolution to the UMK using glass plates. However, rapid progress in the development of CCD
technology promises that higher resolution cameras will be available soon. The ADAM-Topocart analytical stereo-restitutor conversion used in processing the test survey is an
example of a stereo-restitutor, where x, y operator control forms the user input into the computer-
controlled restitutor. Additionally, the operator removes horizontal parallax p with the 'z wheel'. Analytical stereo-restitutors permit continuous measurement as they operate under computer control,
restoring the stereo-model in 'real time'. Stored orientation parameters and systematic model
correction data are then used to generate q parallax carriage translations, which preserve the stereomodel free from vertical parallax q for the viewer. All x, y instrument co-ordinates are
automatically transformed to object co-ordinates, using stored interior and exterior information. The
resolution of the ADAM measuring system is one micrometer. The ADAM-Topocart conversion kit
from the older Zeiss-Jena analogue 23x23cm format stereo-restitutor costs approximately USD 35k; while the newer technology full 23 x 23cm format analytical stereo-restitutor ADAM Promap by the
same firm costs USD 50k.
Other forms of modern stereo-restitutor, falling into a cheaper category of equipment, include such
devices as Leica's Digital Video Plotter "DVP". However, DVP does not contain any plotter build in,
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so, from design concept point of view, should be named as a digital video stereo-restitutor. DVP fulfils two essential functions of stereo-restituting and stereo-digitising of a real 3D oriented model,
which are attributes of stereo-restitutor. Therefore, DVP is essentially a digital image-based stereo-
video-restitutor, which might serve as an inexpensive substitute for the ADAM-Topocart or others, especially when used directly with digitally captured images on CCD camera.
Fig. 2.3. ADAM-Topocart analytical stereo-restitutor.
2.2. THE AUBACORA PROJECT - A PRACTICAL STEREO-PHOTOGRAMMETRIC
SURVEY OF A FISHING VESSEL
In order to evaluate the practicalities of a stereo-photogrammetric vessel surveys, it was necessary
to carry out, at least in part, the photogrammetric documentation of a vessel. While ships of overall length 20 to 50m were considered suitable for such a project, the issue of physical accessibility was an
important parameter. This latter constraint brought to bear on the location of the vessel during the
survey. A choice was therefore made between one of two sites on the Cape Town Waterfront:
Robinson Dry Dock (supporting vessels longer than 100m), and the specialized shunting system called a synchro lift (using which, lighter and shorter vessels may be hauled out of the water, and onto dry
land). When it was learned that the fishing vessel Aubacora, belonging to Tri-Ocean Marine, was
available for a minimum period of ten days on Lane 3 of the synchro lift, it was decided to mobilize.
A reconnaissance survey was first made of the general working area at the synchro lift. This
entailed taping distances between adjacent lanes, so as to determine the maximum subject distance available (typically 5 to 7 meters) for taking the photographs at a later date. A strip of recce
photographs of the Aubacora, taken with a hand held Ricoh KR5 Super with 55mm lens, were used
later to plan the location of control targets. The reconnaissance survey, which included general
familiarization with the work site, took some two hours.
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Fig. 2.4. Diagram of ADAM-Topocart analytical stereo-restitutor.
2.2.1. Co-ordinate Systems Used in the Aubacora Project
Fig. 2.5 illustrates the several co-ordinate systems encountered in the Aubacora project. Three
principal co-ordinate systems are distinguishable: the theodolite observation system; local survey control system; and the vessel reference system used in stereo-restitution. The survey system was
chosen simply as a three dimensional, left-handed system, with the direction of the Z axis coinciding
with the local direction of gravity. All theodolite observations were made in this context; subsequent network adjustments took place in the same system. A right handed local system adopted S9 as the
origin, with S0 constrained to lie on the positive X-axis. In order for the theodolite observations to be
correctly processed by the intersection program used, the left-handed horizontal observations had to be
transformed into this co-ordinate system. The ADAM-Topocart stereo-restitutor requires the three-dimensional object (vessel) co-ordinate system to be right-handed, with the positive Z axis extending
toward the camera station. In this case, the origin of the system was made to coincide with the vessel
target AFT-RUD, situated at the aft rudder post. The positive X axis was constrained to pass through the target FWD-L, the lower, forehead-most hull target.
2.2.2. Establishing the Control
A series of ten theodolite stations was coordinated in a local trilateration network surrounding the
Aubacora. A Wild TC 1000 Total Station (single second), and a single prism, were used for all the
observations. Final 2D (Y,X) co-ordinates were obtained in the left-hand theodolite observation system by performing a least squares trilateration adjustment; S9 was treated as the origin, and S0 was
constrained to lie on the negative X axis. The stations finally used in the control net were heighted
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separately and reciprocally , giving a final disclosure of 1mm, and standard deviations of a final mean height varying from 1 to 3mm.
Fig. 2.5. Diagram of photogrammetric coordinate system.
The use of analytical stereo-photogrammetry and -restitution methods required individual stereomodels to be oriented 'absolutely', i.e. within a fixed object control system, by means of a
minimum of four X Y Z coordinated targets. As an empirical check on the calculation, several chalk
marks were made along the hull so as to demarcate the physical limits of UMK and Mamiya
photographs, using their respective viewfinders. Each photo was to contain six control points in the stereo pair in order to ensure that each photograph in the strip formed part of two models and still
enjoyed a sensible overlap. Using a 'footprint' of 10.8 m, this would mean that the interval between
target pairs would have to be nominally 5m.
A set of targets was made consisting of a 100 x 100mm black paper background, onto which a
white dot was stuck, approximately 25mm in diameter. This was in turn stuck to the back of a section of clear adhesive film; the film was then pressed to the ship's side. A small square of double sided
tape, directly behind the dot, assisted with the adhesion. In addition to these targets, rigid plywood
targets (black background with white dot, as before) were used to identify certain features. Such
features included FWD-U and FWD-L, the two forehead upper and lower points on the ship's stem; and AFT-RUD, a point on the rudder post, right aft. These three points were later used as 'hard' points
in the transformation from ground control co-ordinates to the ADAM-Topocart's object co-ordinate
system. This latter target design was very satisfactory in terms of adhesion and clarity. BROWN (1984) suggests a much smaller white dot diameter of approximately 6mm in order to produce a 60
micrometer diameter point in the stereomodel (at 10m subject distance and 90mm PD.). However,
FLOREK (1994) is in favor of the diagonal, black and white type of target, because of its effectiveness regardless of photo scale. Application of the targets was straightforward. The total time taken to
apply all 16 port targets, including annotating the hull with the target names in chalk, was
approximately 50 minutes.
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2.2.3. Coordinating the Hull Targets
Both faces of the theodolite were read for horizontal and vertical observations, with the mean taken
for each. This meaning procedure was of particular importance owing to some of the steep vertical angles measured; the effects of collimation axis error, horizontal axis error, and vertical circle index
error being thereby negated. Horizontal directions were referenced to the network itself. That is, one
or more (up to three) orientation directions were observed, ending on a single R.O. In this manner, each target was intersected by two rays or very occasionally three. The port side reduced observations
and corresponding observation station co-ordinates were processed by an intersection program
designed by Mr G. van der Vlugt from the Department of Surveying and Geodetic Engineering,
University of Cape Town. Precision estimates for X,Y co-ordinates were naturally not available for two-ray intersections, but RMS errors were estimated from error theory to be about 5mm.
2.2.4. Photography
A metric Zeiss UMK 10/1318 camera was used with Ilford cut film to take photographs of the
entire port side of the vessel. To investigate the suitability of non-metric cameras for documenting a
vessel hull, it was decided to also take photographs with a non-metric Mamiya C330 camera, calibrated by ADAMS (1980). The Mamiya used Fujichrome ASA 100 color slide film. Prior to any
photography taking place, suitable locations for each camera station were marked on the ground, to
within approximately 0.5 m. These stations were decided on by inspection, using the viewfinders of the UMK and Mamiya cameras. Typical subject distances for the UMK and Mamiya were 8 and 18m
respectively. Calculations for depth of field, coupled with light meter readings, prescribed the use of
1/32 f-stop and 1/4 second camera settings for the UMK. The Mamiya photographic work, performed the next day, used similar settings. Ten UMK exposures were made of the Aubacora's port side, from
eight camera stations. The UMK was mounted on a survey tripod, approximately levelled and
nominally oriented at right angles to and tilted 15 degrees upwards from the horizontal. Final
exposures were taken once it was ascertained that all three vertical pairs of control targets were in view. A similar procedure was followed for the Mamiya photographs, albeit from different stations.
On account of the bulky equipment associated with the UMK camera, the port side photography took
approximately three hours to complete; the Mamiya photography was completed within fifty minutes.
2.2.5. Stereo-processing on the ADAM-Topocart Analytical Stereo restitutor
Model Name A4A5UMK MAM11-12 A5B6UMK MAM10-11
Camera used UMK Mamiya UMK Mamiya
Photo pair A4, A5 11,12 A5, B6 10-11
Film make Ilford Fujichrome Ilford Fujichrome
Film speed ASA 110 ASA 100 ASA 110 ASA 100
Film type b&w colour-dia b&w colour-dia
Subject distance 8 m 18 m 8 m 18 m
Effective P.D. 100.35mm 83.00mm 100.35mm 83.00mm
Photo format 166x119mm 57x56mm 166x119mm 57x56mm
Photo Scale 1:130 1:220 1:130 1:220
# Control points 4 6 4 6
# Pass points 3 3 4 2
X RMS [mm] 3 5 1 12
Y RMS [mm] 3 6 2 12
Z RMS [mm] 4 16 2 33
Tab. 2.1 - The final orientation results from the ADAM-Topocart for all four models
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Two stereomodels from each of the UMK and Mamiya sets of photographs were restituted on the ADAM-Topocart. In order for the ADAM-Topocart measurements to be meaningful with respect to
the vessel itself, the hull targets, coordinated in the local survey system, had to be transformed. The
ADAM-Topocart orientations were carried out with the relative/absolute exterior parameters being computed automatically and simultaneously, using a bundle adjustment. The final interior and
exterior orientation results for all four models are given in the accompanying Tab. 1 Once the models
had been oriented, a Feature Code list was set up to aid digitising. The following hull features were identified and digitized in full XYZ co-ordinates:
hull features (pipes, hatches, etc.)
rust patches;
weld lines; control targets;
spot shots
damage areas. A sample of each of these feature types was captured using the ADAM-Topocart's ASCII digitising
data format.
Fig. 2.6. UMK photo of a ship
2.3. DISCUSSION AND ANALYSIS
The literature reveals a strong need for independently verifiable, technical information, concerning
the dimensions and structural integrity of vessels in general. Classification Societies, independent Marine Surveyors, and certain government bodies, exist in the maritime environment for this very
reason. While some of their methods of measurement and investigation may seem crude, it should be
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borne in mind that the question of a vessel's seaworthiness may often be resolved by simple inspection. Moreover, mensuration is often carried out at levels of precision consistent with vessel
fabrication. Nonetheless, marine underwriting bodies have clearly expressed the desire for more
verifiable, reliable information concerning a vessel's condition. This concern is expressed in particular for older vessels.
A stereo-photogrammetric survey of a vessel hull performed in a dry dock condition should have a well-established control net, observed without the hindrance of obscuring vessels. The surveyor can
then choose suitable theodolite observation points from which to fix the hull control. Inadequately
fixed, or distorted hull control, will introduce Y-parallax into the related stereo-model. This, in turn,
results in inaccurate X,Y,Z co-ordinates for measured model points.
While in this project the Mamiya camera was considerably faster to deploy on site than the UMK,
an experienced operator might narrow the time difference considerably. It is therefore not advisable to make inferences based on deployment time alone. However, it must be borne in mind that the full
complement of UMK equipment is over ten times as heavy as the Mamiya camera itself. At a camera
station with restricted movement; on a working site busy with traffic; or between brief periods of
sandblasting, rapid camera deployment is a distinct advantage. The RMS errors of X,Y,Z co-ordinates for an exterior orientation are directly related to the accuracy of observed control targets. In a stereo-
model, this accuracy can be interpolated to any other well-defined point, observed within the limits of
the model control. The practical proof of this statement is the visual comparison of general q-parallax in the stereo-model, before and after the introduction of 'absolute' control. If there is no discernible q-
parallax at any point in the model after relative orientation, the introduction of an accurately co-
ordinated set of control points should not change this situation. Y-Parallax problems will thus be traceable to poor control, or poorly observed points. In this regard, all the UMK stereomodels were
well oriented. The orientation results of the Mamiya cameras, when compared with UMK results, are
also very favourable. An increase in RMSe values for Z, compared to their X,Y counterparts, is the
result of an insufficiently accurate Mamiya Principal Distance PD value, used in the restitution calculations. Stereo-digitised in full 3D format are immediately ready for further processing on any
appropriate CAD package. An example of the stereo-digitised model, plotted from a CAD package
may be found in Fig. 2.
2.4. CONCLUSIONS AND RECOMMENDATIONS
The test survey carried out on Aubacora, as well as the literature researched and explored, permit
the following conclusions and recommendations to be drawn. These conclusions support the use of
stereo-photogrammetry in vessel hull documentation survey for non-specific insurance purposes.
2.4.1. Conclusions
1) There is a need for technical survey documentation of marine vessels. The marine insurance industry relies on sound technical information in order to make realistic actuarial assessments
of insured hulls.
2) Photogrammetric methods are suited to vessel hull documentation. Photogrammetric records
(photographs or digital images) represent databases of great detail; they are compact, permanent and make economical archives. The information contained within the vessel
photographs may be independently verified, at any future date.
3) Stereo-photogrammetric documentation is highly applicable to vessel surveys. A documentation survey provides a general survey of a structure, the final applications of which
are not exactly known a priori, although the surveyor has a good understanding of the scope of
his client's future requirements. Reliability and precision of stereo-photogrammetric survey
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methods is higher than that of the original vessel construction control, and is therefore acceptable.
4) Non-metric analogue and CCD cameras are suitably accurate substitutes for metric analogue
or digital CCD cameras. Provided the non-metric camera is well calibrated for a working subject distance, such a camera may be successfully used for stereo-photogrammetric
documentation of a vessel hull. However, the non-metric camera has to be fully calibrated or
self-calibrated in order to be a sufficiently reliable instrument.
5) Stereo-photogrammetric vessel documentation using Black & White film assists in feature
definition. B&W film, and in particular using B&W negatives, allows the stereo viewer to
discern fine hull features, which are difficult to perceive using colour film.
6) CCD cameras provide fully digital stereo-photogrammetric processing. Rapid progress in the development of CCD cameras promises that these cameras, being laboratory tested with
resolution above 24 megapixels, are available on commercial markets. Thus digital video
stereo-photogrammetry will be better applicable for precise engineering surveying.
2.4.2. Recommendations
a) Marine underwriters should compel underwritten vessels to undergo periodic photogrammetric surveys. The period during which a vessel is compelled to dry dock,
typically for statutory or classification marine surveys, it can be productively used; a
photogrammetric survey of the hull ought to be undertaken for insurance documentation purposes. Photogrammetric surveys should therefore be performed every four or five years,
beginning immediately after construction, and prior to launching. The photographs will be a
historical record of the insured vessel's service life and physical condition. b) A photogrammetric vessel survey should use stereoscopic methods. Any part of the vessel
hull, recorded in the photographs of a stereomodel, may be stereoscopically restituted at any
future date. No prior specification of the features to be measured is required at the
photographing stage, this criterion being essential for a documentation survey. Stereoscopy will assist in interpreting vessel features by recreating the perception of depth, and is thus
recommended.
c) Non-metric cameras, well calibrated for a working subject distance, should be used to perform stereo-photogrammetric vessel surveys. The expense of full-blown metric cameras can be
obviated by using non-metric cameras, providing that calibration is performed at an
appropriate subject distance for vessel surveys. d) Stereo-photogrammetric documentation surveys should principally make use of Black &
White film. B&W negatives will enhance the interpretative aspect of the photographic
documentation. Experimentation with other types of film, such as B&W infra-red, might
prove successful in recording subtle or invisible details. Simple colour photographs of deck spaces and superstructure can broaden the scope of the survey.
e) CCD cameras should be considered as a tool for vessel hull stereo-documentation. Maturation
of CCD camera technology and availability of digital video stereo-restitutors will ultimately enhance the Engineering Surveyors' repertoire of measurement tools. CCD cameras will then
find useful application in vessel hull stereo-documentation surveys for marine insurance
purposes.
REFERENCES
ABS. 1994: "New Ideas For Existing Hulls", Special Publication by American Bureau of Shipping
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ADAMS LP. 1980: "The Use of Non-metric Cameras in Short Range Photogrammetry", Archives of 14th ISP Congress, Hamburg
BROAD G. 1994: Correspondence with the writer by facsimile, September
BROWN DC. 1984: "Close Range Photogrammetry and Surveying - State of the Art", Workshop Proceedings,
ASPRS
BV. 1989: "What is a Classification Society ?", Special Publication by Bureau Veritas Courbevoie
FLOREK R. 1975. "Możliwości pomiarów szybkozmiennych odkształceń kadłubów morskich statków metodą
fotogrametrii", (Possibilities of Deformation Measurements of the Sea Vessel-hulls using
Photogrammetry). In: Materiały Konferencji SGP "Geodezja w gospodarce morskiej", Gdansk,
Poland, pp.88-83
FLOREK R. 1988: "Improvement of Photogrammetric Methods Used for Constructing, Mounting, and
Exploitation of Engineering Structures", (in Russian). Materialy Konferencji Specjalistow Sluzb
Geodezyjnych KS nt. "Automatyzacja prac geodezyjno- inzynierskich", IGiK, Jadwisin-Warsaw,
Poland, pp.1-57. GOWANS B. 1994: Interviewed by the writer at Maritime & Industrial Services Head Office, on 30 June 1994
GUY J. 1989: "Marine Surveying & Consultancy", Fairplay Publications HON J. 1994: Correspondence with the writer by facsimile, August
KEMP JF. & YOUNG P. 1989: "Ship Construction Sketches and Notes", 3rd Ed., Heinemann Newnes
KENEFICK JF. 1977: "Applications of Photogrammetry in Shipbuilding", Photogrammetric Engineering &
Remote Sensing, September
LENZ R, BEUTLHAUSER, & LENZ U. 1994: "A Microscan/Macroscan 3x12 Bit Digital Color CCD Camera
with Programmable Resolution up to 20 992 x 20 480 Picture Elements". Proceedings of the
Commission V Symposium - Close Range Photogrammetry and Machine Vision, International
Archives of Photogrammetry and Remote Sensing, Vol.XXX, Part 5, pp.225-230
MATHESON HDM. 1994: Correspondence with the Author on 25 July and interview
OLIVER PRF. 1994 "Close-range Photogrammetry of a Ship's Hull - Implications for Marine Insurance". B.Sc.
(Hons.) Surveying Thesis, University of Cape Town
STAMPA HR. 1980: "The Development & Testing of.. using the Mamiya C330F Cameras in Short-range Photogrammetry", B.Sc. (Hons.) Surveying Thesis, University of Cape Town
STD. BUL. 1994: "Classification of Ships", The Standard Bulletin, Issue 22, May, p.4
STIRLING DM. 1990: "Close-range Photogrammetry", Engineering Surveying Technology, Chapter 8, Blackie
TARGGART R. 1980: "Ship Design and Construction", The Society of Naval Architects and Marine Engineers,
New York
TAYLOR DA. 1987: "Muckle's Naval Architecture", 2nd Ed, Butterworths
THOMSON MM. 1980: "Manual of Photogrammetry", American Society of Photogrammetry, 4th Ed., Virginia
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3. THEMATIC MAPPING AND PHOTOGRAMMETRIC
MEASUREMENTS OF JOHANNESBURG AREA,
FROM SATELLITE MK-4 CAMERA PHOTOGRAPHS
This chapter sets out the results of investigations and practical tests of stereo restitution and stereo
digitizing of a 3D-model produced from 1:890,000 Russian space photographs of the Johannesburg
area, South Africa. The photographs were taken using a MK-4 space photographic camera with a size of 180mm x 180mm, a principal distance of 300mm and a flying height of 268km.
The MK-4 camera consists of four lenses and can be used as a multispectral. A three layer color spectrozonal film can also be applied for ready IR false color compositions in the range of 580-800
nanometers. The stereorestitutor was calibrated to glass rectification plates (size 230mm x 230mm)
with a 10mm grid. The stereomodel was oriented and corrected with regard to the following model
disturbances: 1. Film deformations;
2. Symmetric radial distortion;
3. Atmospheric refraction; 4. Earth curvature.
The ground control points were taken from a 1:10,000 orthophoto map. Many different features
were examined as possible reference points for model scaling and external absolute orientation. These features include: road intersections, corners of fields and houses, tree lines, rivers and canals. Different
combinations of control points were applied for absolute orientation. The best results were achieved
using eleven control points with RMS errors of approximately 8 meters on the ground.
The important component of photointerpretation was applied in order to provide control points and
to later aid in the stereo digitization of the corrected and oriented model. A sample of a land-use thematic map of a chosen area was then produced. The conclusions and recommendations obtained
from these investigations may be useful for potential users of satellite photographs for thematic
mapping.
3.1. PHOTOGRAPHY FOR SPACE MONITORING SYSTEMS
The practical aspect of this report involves the stereo restitution of a pair of Russian space photographs of the scale 1:890,000 on an analytical stereo restitutor to form a corrected three
dimensional (3D) model. Photographic emulsions which are applicable to monitoring systems can be
classified as follows: one layer Black and White; one layer Infrared Black & White;
three layer Color;
multilayer Spectrozonal.
The sensitivity of a multilayer spectrozonal emulsion extends into the infrared region. One layer is sensitive to infrared radiation and the other layers are sensitive to different regions within the visible
spectrum. The final image is in false color and can be used for photo-interpretation, thematic and
topographic mapping and other geomatics processing. Owing to the advances in the operational capabilities of sensor platforms and the development of fine grained, high resolution photographic
emulsion, most camera systems now include not only fiducial marks or reference grids, but image
forward and angular motion compensation devices as well.
Satellite photographs can help generate thematic and topographic maps in medium (about 1:25,000
- 1:50,000) and small ( =< 1:100,000) scales much quicker and cheaper than conventional methods.
This is of particular advantage to developing countries. Satellite photography should be viewed as
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being complementary rather than competitive to the electro-optical monitoring systems like LANDSAT and SPOT.
1. In order to fulfil mapping requirements at 1:100,000 and 1:25,000 scales, the following criteria should be met [Konecny 1984]:
2. Resolution must be enough to show an object on the map (+/- 5m on 1:25,000 and +/-10m on
1:100,000); 3. The geometry must be reconstituted to +/- 10m for 1:25,000 and to +/- 20m for 1:100,000;
4. Imagery must allow for the determination of 25m contours.
3.2. MK-4 SPACE PHOTOGRAPHIC CAMERA
The MK-4 camera system consists of four lenses and four out of six bands or band combinations
may be selected for a certain earth coverage. The MK-4 camera is mounted on the Resurs-F2 spacecraft and is capable of taking pictures of the entire earth twice, or three times, during its 30-day
mission. The technical data of the MK-4 are as follows:
Principal Distance: 300 mm
Photograph Size: 180 mm x 180 mm Flying Height: 200 - 300 km
Photo Scale: 1:650,000 - 1:1,300,000
Area Coverage: 117 km x 117 km - 216 km x 216 km Ground Resolution: 6 - 8 m
Reference grid: Yes, 5 x 5 with 40 mm spacing
Bands: Z1 635 - 690 nm (B & W)
Z2 810 - 900 nm (IR B & W)
Z3 515 - 565 nm (B & W)
Z4 460 - 505 nm (B & W) Z5 580 - 800 nm (Spectrozonal False Colour)
Z6 400 - 700 nm (Colour)
The MK-4 film format of 180 mm x 180 mm allows photos to be easily evaluated on conventional
photogrammetric equipment such as an analytical stereo restitutor. The 60% forward overlap allows
stereo observation, 3D model restitution and stereo digitizing for the compilation of maps with positional accuracies of +/- 10m and elevation accuracies of +/- 15m, depending on the accuracy of the
ground control. Cost per sq km of image is USD 0.04 comparing to USD 0.14 for LANDSAT TM and
USD 0.74 for SPOT-Pan.
3.3. CONTROL AND RESTITUTION OF THE 3D MODEL
A pair of a MK-4 band Z1 photos in the range 635 - 690 nm of the Johannesburg area were used in the practical portion of this investigation. These photographs were used to form a three dimensional
model on the Adam Topocart analytical stereo restitutor. Coordinates of the projection center were as
follows:
Photo Number Latitude Longitude
0305 26 31' 27 22'
0306 25 50' 27 27'
Date of photography : August 18, 1989
Altitude of photography : 268.1km
Principal distance PD : 300.024mm
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Film type : T-27 (B & W) 635-690nm Resolving power : 195 l/mm
Ground coverage : 160km x 160km
Scale : 1:890,000
With satellite photography, control cannot be premarked on the ground. Reliance has therefore to
be placed on features which are identifiable on the satellite photographs. These features include: road intersections, corners of fields and houses, tree lines, rivers, canals, etc. The location, co-ordination
and heighting of these control points poses a problem. Three techniques of solving this problem were
attempted:
1. Contact printing and enlargement; 2. Slides 1:1 projected to 100:1 image;
3. Orthophoto maps 1:10,000.
This proved to be a fairly successful method for control point identification, especially the slides
which, once projected, allow for reasonably easy feature identification. For this experiment, in
addition to the Johannesburg photos, satellite photographs of the Munich area in Germany were used.
The Munich photographs were taken using a KFA-1000 camera with SN10 Spectrozonal film of the bands 560-680nm and 680-810nm. Locating and coordinating control points from 1:10,000 orthophoto
maps involves the identification of features (e.g. road intersections in the model), then locating the
orthophoto map on which that feature occurs. The coordinates would then be scaled off the orthophoto in the Gauss Conform coordinate system and the heights interpolated from 5 meter contour lines. The
most identifiable features in the stereo model were roads and road intersections, water features and
tree lines.
As the ground coverage is so large (160km x 160km), it spans two or three lines of longitude. The
South African co-ordinate system is based on the Gauss Conform Projection. The system consists of a
number of two degree wide zones, each with its own local co-ordinate system. Of the control points adopted, the majority are on the zone centred on the 27° line of longitude (Lo27), while a few are on
Lo29. A zone-to-zone transformation is required in order that all points are in the same co-ordinate
system. It was decided to use Lo27 as this zone contains the majority of points.
3.4. CORRECTIONS APPLIED TO STEREO MODEL
The photographs were taken from a high altitude of 268km. It was therefore essential that
corrections for earth curvature and atmospheric refraction be applied. These corrections were
incorporated with the lens distortion correction (radial and asymmetric in the form of an odd-powered
polynomial) and then applied. An absolute exterior orientation was to be computed using combinations of 12 of the control points entered. For a model of this scale and with the accuracy of
control being used, standard deviation of 10m in the X and Y ground co-ordinates and 20m in the Z
co-ordinate could be achieved.
After the absolute exterior orientation had been completed, the next step was to produce a thematic
map of a portion in the stereomodel. The digitized area contained such features as rivers and dams,
roads, urban areas and cultivated land. The area was digitized at a scale of 1:36,000 (chosen as it facilitated easy viewing on the screen) in line and continuous mode. A sample of the map is attached.
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3.5. CONCLUSIONS
Based on the findings of these investigations, the following conclusions may be drawn:
1. The stereo restitution of satellite photographs can be accomplished with acceptable accuracy and the quality of the stereo model produced is sufficient to enable digitizing;
2. The stereo digitization of satellite photograph models enables the production of medium
or small thematic and topographic maps;
3. The method of scaling co-ordinates off 1:10,000 orthophoto maps provided sufficiently
accurate ground control for the restitution of the satellite photos;
4. The corrections for earth curvature, atmospheric refraction and lens distortion must be
sufficiently modelled by the software to avoid decreasing the accuracy of the absolute exterior orientation;
5. It is possible to compile or revise a thematic map from satellite photographs with
sufficient feature identification and accuracy.
BIBLIOGRAPHY
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Konecny G., (1984) The Evaluation of Spacelab 1 Photogrammetric Camera Data, Int. Arch.
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the cameras KATE-140, KATE-200 and KFA-1000. Int. Arch. Phot. Rem. Sens. Vol2, pp.506-511. Liebig V., (1992) New Satellite Data with High Ground Resolution from the Space Complex MIR and other
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