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Section 5

Orthoimage generation

Emmanuel Baltsavias

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Orthoimage Generation

Older sensor models methods:

• Kratky’s Polynomial Mapping Functions (PMFs)

• Relief corrected affine transformation

- Project GCPs on reference plane (X, Y coordinate corrections) using sensorelevation and azimuth

- Reference plane -> reference plane of DTM

- Compute affine transformation between X, Y object and x, y pixel coordinates

- 3 GCP’s are needed but 4-6 are suggested

Current method:

• Use RPCs and subsequent shifts or affine transformation

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Orthoimage Generation

Test resultsLuzern

Method: Relief corrected affine transformation

Sens elev. (deg) 67.7DTM spacing/accur (m) 25 / 2.5 lowland, 10 AlpsGCP accuracy (m) 0.5 – 3GCP definition Very poor to goodElevation range (m) 400-2100

Version GCPs/CPs RMS/X RMS/Y Max. abs X Max. abs Y1 0 /66 134.2 30.6 501.5 118.12 6 / 65 2.6 2.2 9.9 5.95 6/14 0.6 0.6 1 1.1

CPs = check points

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Orthoimage Generation Test results

Method: Relief corrected affine transformation

Nisyros

Version GCP's/CPs RMS/X RMS/Y Max. abs X Max. abs Y1 0 / 38 106.1 75.5 153.1 122.82 4/34 1.7 1 4.4 2.33 4/15 0.9 0.6 1.5 1.4

Sens elev. (deg) 73.5DTM spacing/accur (m) 2 / 3.3 GCP accuracy (m) ca. 0.5GCP definition Poor to goodElevation range (m) 0-700

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Orthoimage generation (IKONOS, Quickbird) in Geneva

Input data

2 IKONOS Geo images (IKONOS-West / IKONOS-East)1 Basic QUICKBIRD Image

Orthoimages (for acquisition of GCPs):OP-DIAE: Digital Orthos of Canton Geneva (25 cm pixel size, 0.5 m planimetric RMS)Swissimage: Digital Orthos of Switzerland of Swisstopo (50 cm pixel size, 1m planimetric RMS)

DTMs:DTM-AV (from airborne laser scanning): 1 m grid spacing, 0.5 m height RMSDHM25 of Swisstopo (from digitised contours): 25 m grid spacing, 1.5-2 m height RMS

Measurement of GCPs with ellipse fit and line intersection.

Image orientation with various sensor models. RPCs with subsequent affine transformation used fororthoimage generation.

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GCP example: roundabout (Melbourne testfield)

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Roundabout measurement via ellipse fit

Edge points digitized semi-automatically, followed by ellipse fit

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Roundabout measurements via least-squares template matching

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User-interface for GCP measurement & block adjustment (Sat-PP ETHZ)

Ellipse Fitting

Sensor Modeling and Block Adjustment

Ellipse fitting mode

Line intersection mode

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Orthoimage generation (IKONOS, Quickbird) in Geneva

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Orthoimage generation (IKONOS, Quickbird) in Geneva

Pansharpened orthoimages. Left Ikonos, right Quickbird.

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Orthoimage generation (IKONOS, Quickbird) in Geneva

Definition of lines and circles. Left Ikonos, right Quickbird.

Note the large visual difference although pixel size is 1m and 0.7m respectively.

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Orthoimage generation (IKONOS, Quickbird) in Geneva

-0.38-0.080.600.5610/53Quickbird

-0.590.100.760.4710/33Ikonos East

-0.490.250.630.5510/23Ikonos West

Y meanwith sign (m)

X mean withsign (m)

Y RMS (m)X RMS (m)Number of GCPs/CPs

Image

Planimetric accuracy of panchromatic orthos with GCPs from OP-DIAE

(CPs = check points)

Quickbird is not more accurate than Ikonos although GSD was 0.7m and 1m respectively.

Planimetric accuracy could be even higher with well defined GCPs measured with GPS.

In Y mean (bias) large due to coordinate system differences (Geneva and national systems differ).

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Orthoimage generation (IKONOS, Quickbird) in Geneva

-0.11-0.060.770.6610/93Quickbird

-0.330.000.750.6710/57IkonosEast

-0.30-0.070.720.9110/58Ikonos West

Y meanwith sign (m)

X mean withsign (m)

Y RMS (m)X RMS (m) Number of GCPs/CPs

Image

Planimetric accuracy of panchromatic orthos with GCPs from OP-DIAE and Swissimage

Submeter accuracy even with GCPs from not so accurate Swissimage orthos.

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In-depth investigations of parameters influencing the accuracy of orthoimages from high resolution satellites

AIMS

The aim of this work was the analysis of orthoimage accuracy produced from IKONOS and QB images using different type of original data in Switzerland. More specifically, we were interested to see the influence on the planimetric accuracy of

- different sources for the measurement of GCPs (Ground Control Points),

- different elevation models and

- different sensor elevation.

The whole processing was performed mainly with Sat-PP (Satellite Imagery Precision Processing) software developed at IGP which makes use of good quality algorithms, especially for DSM generation and semi-automatic point measurement and feature extraction. The software can be used with any type of imagery, digital and scanned film, frame and linear sensors.

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Specifications of the data

The first area, Thun, lies in the central part of Switzerland 40 km southern of the capital of Switzerland, Bern. In this region in 2004, we established a testfield with a coverage of 15 by 20 sqkm for the analysis of high resolution satellite images.

Later in 2006, this testfield was extended for the analysis of ALOS images to the neighborhood of Bern and Thun (30 by 30 sqkm). In the area of Geneva we used two IKONOS and one QB images. The test area had a size of 16 by 17 km.

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Specifications of used satellite images:

82.1372.206Reverse2003-12-25Thun_I_163003_100

62.95180.39Reverse2003-12-25Thun_I_163003_000

61.6240.2Reverse2001-05-28Geneva_I_East

67.2253.6Forward2001-05-28Geneva_I_West

77.6286.4Reverse2003-07-29Geneva_Q

Sensor-Elevation (deg)Sensor- Azimuth (deg)Scanning modeDate of acquisitionImage

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Resolution and accuracy of used orthoimages and DTMs:

average deviation to DHM25 is about 17

Flat-hilly-Jura: 1.5

Voralps: 2Alps: 5 - 8

0.5/vegetation

:1.5

0.50Accuracy of the height [m]

1.00.50Planimetric accuracy [m]

25025.02.00.501.00.25GSD / grid spacing [m]

DHM25DTM-AVUsed elevation model

LV03LV03LV03LV03LV03-GELV03-GEReference frame

Swiss Federal Office of Topography (Swisstopo)Canton GenevaProduced by

RiminiDHM25 DTM-AVSwissimageDTM-AV OP-DIAE

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RESULTS

Orthoimage accuracy in the Geneva test area:

CPs = check points

Max AbsoluteRMSEMeanNumberof CPs

2.81.11.00.7-0.20.213QB_DHM25

2.61.20.90.6-0.20.213QB_DTM-AV

2.51.71.20.8-0.70.011IKONOS_East_DHM25

2.00.71.10.3-0.70.211IKONOS_East_ DTM-AV

1.81.91.11.00.0-0.49IKONOS_West_DHM25

1.90.81.00.50.00.110IKONOS_West_ DTM-AV

Y (m)X (m)Y (m)X (m)Y (m)X (m)Orthoimage version

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Results from the image orientation in Thun:

GCP = Ground Control Points

0.980.900.7478Orthoimage/DHM252003-10-12

0.690.660.7068DGPS2003-10-12

1.360.600.6048Orthoimage/DHM252003-12-25

0.560.400.37278DGPS2003-12-25

z-RMS [m]y-RMS [m]x-RMS [m]CPGCPType of GCPDate ofImage

Acquisition

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Orthoimage accuracy in the Thun test area:

83ORTHO

83GPS

63ORTHO

63GPS

83ORTHO

83GPS

63ORTHO

63GPS

83ORTHO

83GPS

63ORTHO

63GPS

83ORTHO

83GPS

63ORTHO

63GPS

Type of GCPSensor

elevation Y (m)Y (m)Y (m) X (m)X (m)X (m)Elevation model

Max AbsoluteRMSEMeanNumberof CPs

Orthoimage version

2.43.21.01.10.4-0.310LIDAR

2.12.41.20.8-0.90.311LIDAR

2.82.91.21.20.3-0.611LIDAR

2.02.61.01.0-0.2-0.412LIDAR

2.31.91.00.7-0.40.119Matching

1.91.71.00.7-0.70.217Matching

2.94.01.11.3-0.40.120Matching

3.53.21.21.1-0.50.220Matching

2.61.91.20.8-0.80.119DHM25

3.22.21.30.9-0.90.217DHM25

10.22.43.71.0-0.3-0.120DHM25

9.63.73.61.0-0.40.120DHM25

4.53.52.01.2-0.70.321Rimini

3.62.32.01.0-1.20.421 Rimini

22.95.78.81.7-0.90.120Rimini

22.43.08.01.2-0.90.020Rimini

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Conclusions

High accuracy DTM/DSM, as the DTM/LIDAR and the matching DSM, provide more similar accuracy in X and Y, quite independently of the sensor azimuth and elevation.

As the DTM/DSM accuracy deteriorates, a higher sensor elevation is needed and the height errors are distributed in X and Y differently, depending on sensor azimuth.

For high sensor elevation (in this case 83 degrees), an orthoimage accuracy of 1-2.5 m was achieved even with the RIMINI dataset.

The major influence on the orthoimage accuracy is from the DTM/DSM and the sensor elevation.

The role of GCP accuracy, as long as this is within certain limits (e.g. at least one GSD) is subordinate. Since GCP acquisition is costly and time consuming, the selection of GCP acquisition method should be made based on the accuracy of the available DTM/DSM and the sensor elevation.

Orthoimages with submeter accuracy can be produced even with suboptimal DSMs / DTMs and GCPs. Accuracy can reach 0.5 GSD.