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Survey Technology Best Practices

Part I !!!!!

New$York$State%Association!Of"Professional+Land+Surveyors!

Annual&Conference!2014!!!!

Presented by !

Joseph Paiva - CEO

January 2014

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©$2014$J.V.R.$Paiva$&$GeoLearn,$LLC$ 1$

Survey Technology Best Practices

Part I NYSAPLS Conference

January 2014

Joseph V.R. Paiva

CEO -

Premise !  Technology is becoming increasingly easy to use

!  The variety of technologies accessible to surveyor today are much more than the simple chain, compass or transit and level

!  Many technologies require consideration of the earth’s shape

!  Surveying is increasingly becoming the realm of one person in the field accomplishing the work that was formerly done by a team of 2, 3, 4, 5, etc.

!  So…

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What is potential for mischief?

!  We can today make more mistakes, faster, and bigger than we could with the chain and compass

!  Button pushing means that the data is seldom reviewed

!  More importantly, the comprehensive knowledge about the technology is more and more ignored when viewing data in the field or the office

!  Most surveyors can’t say “geodetic”

!  Many times there is nobody to catch mistakes in the individual, whether in the field or the office

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Outline Pts I and II !  Taping (yes taping)

!  EDM

!  Angle measurement

!  Total stations

!  GPS static

!  GPS kinematic

!  Others (Leveling, UAS, photogrammetry, LiDAR…)

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Taping !  Who does it?

!  Who doesn’t?

!  What are expectations?

!  Of client

!  In the body of knowledge

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Which tape? !  Invar

!  Steel

!  Platic-coated steel

!  Fiberglass

!  Cloth

!  Others…

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Accuracy expectations? !  What field procedures?

!  Bucks

!  Thermometers

!  Tension handles

!  Lining pins/poles

!  Plumb bobs

!  inclinometer

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Tape calibration

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True Length of Baseline (TL) = 100.027 ft

Measured Length (ML) = 100.035 ft

What is the true length of the tape?

i.e. what is the length between the zero and the 100 ft marks?

Answer: 99.992 ft

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Calibration analysis

035.100027.100

00.100=== tape

baseline

baseline

tape

tape TLMLTL

MLTL

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True Length of Baseline (TL) = 100.027 ft

Measured Length (ML) = 100.035 ft 0 ft 100 ft

100 ft

100.027

.035 -

99.992 Alternatively…

[99.9920028]

But… !  Do not calibrate an EDM by comparing the

observation to a stretched out steel tape!

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Understand error sources !  Not horizontal

!  Length in error

!  Temperature expansion

!  Tension expansion

!  Shortening due to sag when end-supported

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Accuracy or Precision? !  Which do you want to achieve?

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Precision !  Fineness of measurement

!  Measure of how closely grouped a number of measurements of the same quantity are

!  Repeatability…

!  Reflection of quality of instrument or least count

!  Expression of the METHODS used

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Accuracy !  Closeness of a measured value to the true value

!  Expression of the RESULTS of measurement

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Which is which? !  Possible to do well in one and horribly in the other

(either precision or accuracy)

!  For the surveyor, because the true value is usually impossible to obtain, the methodology is to:

!  Make redundant measurements

!  Measure all you can about environment and the instrument and correct for biases

!  If blunders have been caught, the resulting uncertainty is accuracy

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Uncompromising accuracy !  Only possible if for all measurements:

!  Redundant measurements

!  Measure …environment and the instrument (i.e. calibration) and correct for biases

!  Find and fix blunders

!  This should be your mantra for all types of technology

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If you don’t want to get “killed”…

!  Then

!  Calibrate instrumentation

!  Make redundant measurements

!  Measure environment and carefully log procedures used

!  Develop procedures to eliminate blunders, develop procedures for identifying blunders (field and office)

!  Be consistent in the practice of these rules

!  But…know what’s important to consider when, and what’s not

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EDM !  True, that EDM is mostly used in conjunction with a total

station

!  But for this part of the discussion, we will consider it separately

!  Do you know the most common systematic errors with EDM use?

!  How do the blunders occur, and what can you do to prevent them

!  What is your EDM’s specified “accuracy”?

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EDM variations !  Infra red vs. laser

!  Phase modulation vs. time-of-flight

!  With reflector vs. reflectorless

!  There are also some robotic-related issues we will touch upon later

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What field procedures? !  Do you measure forward and back?

!  How many repetitions to make a “measurement”

!  How do you do those repetitions?

!  Measure temperature and pressure?

!  How is the effect determined?

!  With prism, how is the prism constant determined?

!  Without a prism, what errors are possible?

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EDM accuracy !  How rated?

!  How to evaluate?

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Line of sight !  Does EDM beam pass close to surface of earth

(potential for vertical refraction)

!  Does EDM beam pass close to other objects to right and left? These may be surveyor’s vehicle, trees, rock faces, etc.? If close, they may be susceptible to horizontal refraction

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EDM accuracy by range Accuracy 100 Ft. 1100Ft. 2200 Ft. 3300 Ft.

±(2mm+2ppm)

±2.1mm=0.007ft

±2.7mm=0.009ft

±3.3mm=0.011ft

±4mm=0.013ft.

±(2mm+3ppm)

±2.1mm=0.007ft

±3.0mm=0.010ft

±4.0mm=0.013ft

±5mm=0.016ft.

±(3mm+2ppm)

±3.1mm=0.010ft

±3.7mm=0.012ft

±4.3mm=0.014ft

±5mm=0.016ft.

±(3mm+3ppm)

±3.1mm=0.010ft

±4.0mm=0.013ft

±5.0mm=0.016ft

±6mm=0.020ft.

±(3mm+5ppm)

±3.2mm=0.010ft

±4.7mm=0.015ft

±6.3mm=0.021ft

±8mm=0.026ft.

±(3mm+10ppm)

±3.3mm=0.011ft

±6.3mm=0.021ft

±9.7mm=0.032ft

±13mm=0.042ft.

±(5mm+2ppm)

±5.1mm=0.017ft

±5.7mm=0.019ft

±6.3mm=0.021ft

±7mm=0.023ft.

±(5mm+3ppm)

±5.1mm=0.017ft

±6.0mm=0.020ft

±7.0mm=0.023ft

±8mm=0.026ft.

±(5mm+5ppm)

±5.2mm=0.017ft

±6.7mm=0.022ft

±8.3mm=0.027ft

±10mm=0.033ft. 22

Temperature and pressure !  Each 1° change in temperature is 1 PPM

!  Each 1 inch (approx) of mercury change in atmospheric pressure is about 10 PPM [therefore 0.1 inch ≈ 1PPM [0.1” Hg ≈ 100 ft elev change also]

!  What do you do?

!  If your survey is being done at 45°F and an atmospheric pressure of 28.7 inch Hg, what is the PPM value? In 1000 ft, what is the error if uncorrrected?

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PPM error calculation !  If EDM’s zero-zero value is at 0°C (32°F) and 1

atmosphere (29.92” Hg)

!  ∆ temp = +13°F ≈ 7°C = +7 PPM

!  Thus apparent distance is shorter if uncorrected, as the air is thinner, thus allowing light to travel faster

!  ∆ pressure = +1.22” Hg ≈ +12 PPM

!  Thus apparent distance is shorter if uncorrected, as air is thinner, thus allowing light to travel faster

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Total PPM error !  Add the two together to get +19 PPM

!  In 1000 ft, if uncorrected this error amounts to a 0.019 ft shortage (correction is +0.019 ft)

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Calibration !  CBL distributed around U.S.

!  If local surveyor does not use this, how is there some assurance that the EDM is functioning properly?

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Optical plummets !  When were they checked last?

!  How does one check them?

!  What is your record of such checking?

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Level bubbles !  Errors in bubbles mean that optical plummets (or

prism poles) are not level when the bubble is centered?

!  How to check?

!  If upon checking you determine error, how do you calculate impact?

!  Is there a way to correct for lack of adjustment in the bubble(s)?

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Level vial centering/adjustment

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Prism constant !  Is the correct one being used?

!  What is the impact?

!  What about when using no prism?

!  What if one forgets and switches from prism to no prism or vice versa?

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Determining prism & instrument constants

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A B C

AB + BC should equal AC

If error exists (e), then

it will be in each of the measurements, thus

AB + BC – AC = e

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Q & A

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About&the&seminar&presenter& Joseph V.R. Paiva, PhD, PS, PE Joseph V.R. Paiva is CEO of GeoLearn, LLC (www.geo-learn.com), which is launching an online professional education business for the geospatial industry in early 2014. Joe started this business with his partner Bob Morris, whose most recent global industry position was President of Leica Mapping. Previously, Dr. Paiva was CTO of SADAR 3D and COO of Gatewing NV, a Belgian unmanned airborne systems company. Prior engagements in consulting were in the field of geomatics and general business, particularly to international developers, manufacturers and distributors of instrumentation and other geomatics tools. Dr. Paiva and Mr. Morris continue to be involved in consultancy through a separate partnership called GeoSpatial Associates, LLC will continue this consultancy. Joe’s career includes: managing director of Spatial Data Research, Inc., a GIS data collection, compilation and software development company; various assignments at Trimble Navigation Ltd. including senior scientist and technical advisor for Land Survey research & development, VP of the Land Survey group, and director of business development for the Engineering and Construction Division; vice president and a founder of Sokkia Technology, Inc., guiding development of GPS- and software-based products for surveying, mapping, measurement and positioning. He has also held senior technical management positions in The Lietz Co. and Sokkia Co. Ltd. Prior to that was assistant professor of civil engineering at the University of Missouri-Columbia, and a partner in a surveying/civil engineering consulting firm. He has continued his interest in teaching by serving as an adjunct instructor for online course development and teaching at the Missouri University of Science and Technology. His key contributions in the development field are: design of software flow for the SDR2, SDR20 series and SDR33 Electronic Field Books and software interface for the Trimble TTS500 total station. He is a registered Professional Engineer and Professional Land Surveyor, has served as ACSM representative to the Accrediting Board for Engineering and Technology (ABET), serving as a program evaluator, team chair, and commissioner and has more than 30 years experience working in civil engineering, surveying and mapping. He writes for POB, GeoDataPoint and The Empire State Surveyor magazines and has been a past contributor of columns to Civil Engineering News. Joe has also been a consultant to the Geomatics Industry Association of America, later reorganized under the Association of Equipment Manufacturers (AEM) as the Geospatial Industry Group, Joe has organized and presented workshops and authored and edited articles for the technical press in this role. Joe can be contacted at [email protected]

January 2014

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