What is Stereo imagesWhen two images is capture from different location of same area than common in two image will produce the depth information such pair called stereo image.

Art Institute of Chicago Lion Statue (parallel stereo pair)

History Stereoscopy

Jacopo Chimenti (c 1551 - 1640), an artist

from Empoli, made two sketches of a young

man holding a compass and a plumb line.

When these were seen, mounted next to

one another, by Alexander Crum Brown in

1859, he combined them by over

convergence and described the stereoscopic

depth he saw. Digital elevation model can be

generated if we can extract X, Y, Z for each

point from a image.

Aime Laussedat (1819-1907) is regarded by many as the “father of photogrammetry.” due his pioneering work in photogrammetry.

Height measurements

1. Relief measurements

ha =

d – relief displacement

r – radial distance

For this method ‘d’ should be measurable on photograph. As ‘d’ is inversely proportional to HThis can’t be

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2. Parallax measurement

ha = H -

Where,

B - Airbase,

f - focal length,

H - height above datum,

ha - height of terrain above datum

Stereoplotters

Stereoplotters are the instruments used to extract the 3-D topography from stereo

images. types of stereoplotters available

Optical

mechanical

Optical-mechanical

Analytical

Digital photogrammetric system

Automated stereoplotters

Optical-mechanical stereoplotters basics In Stereoplotters 3 orientations helps to create the similar model of ray as it was the time of photo taken1. Interior - In this orientation dia +ve can be moved to fix the principle point

also called colinearity condition.2. Relative – Aim of this orientation to fulfill the coplanarity

this said to be achieved if five pair of rays intersect.this is done by projector S1&S2 up and down this lead to change in X, Y, Z and also dia +ve allowed to rotate about X, Y, Z (ω , , k). These motion can be apply for both images hence 12 motion are involved in this orientation.

3. Absolute - In this orientation scaling and levelling is adjusted through moving base table. Here base table can be

moved up & down for scale adjustment and for levelling table is tilted about X or Y.

f

These orientation are capable of removing any type error due to translation, rotational tilt ect.. Using integrated GPS and IMU device we can avoid this complexity.

Zhilin 2004

Direct Linear Transformation model

x = −f

y =

XS, YS, ZS is the set of ground coordinates of projection center S in the geodetic coordinate system; XA, YA, ZA is the set of ground coordinates of point A in the geodetic coordinate system; f the focal length of the camera; ai , bi , and ci (i = 1, 2, 3) are the functions of the three angular orientation elements (i.e., φ, ω, κ) as follows:

a1 = cos φ cos κ + sin φ sin ω sin κb1 = cos φ sin κ + sin φ sin ω cos κc1 = sin φ cos ωa2 = −cos ω sin κb2 = cos ω cos κc2 = sin ωa3 = sin φ cos κ + cos φ sin ω sin κb3 = sin φ sin κ − cos φ sin ω cos κc3 = cos φ cos ω

Similarly other models also developed for transformation like Rigorous Sensor Model (RSM), Rational Functional Model, Self Calibration Direct Linear Transformation (SDLT).

VHR satellite provide stereo image

There large of satellite provide stereo image list is given next.

Stereo image can be acquire either along path or across path of satellite orbit.

VHR satellite generally capture in pan-band and multispectral band for high resolution.

Minimum the pixel size lesser will be the error in measurements.

ID Satellite/Sensor Country/Comp any Date of lunch Resolution

(stereo image) Min/Max (m)

Swath Width Min/Max

(km) Stereo B/H

1 IKONOS 2 USA/GeoEye 24 Sep 1999

Pan (N) 0.8 Multi (N) 3.2

Pansharpened 0.8-1.0 11*11 Along -track 0.54-0.83

2 EROS -A1 Israel/ImageSat 5 Dec 2000 Pan (N) 1.9 14*14 Along –track Across-

track variable

3 QuickBird USA/Digital Globe 18 Oct 2001

Pan 0.61 Multi 2.4 16.5*16.5 Along -track 0-6 to 2.0 most collections

between 0.9 and 1.2.

4 Spot 5 France /Spot image

4 May 2002

Pan 2.5-5 Multi 10 60*60 Along- track

Across-track Variable

6 CartoSat -1 India 5 May 2005 Pan 2.5 26*26 Along-track 0.62

7 ALOS(PRISM) Japan 24 jan 2006 Pan 2.5 35*35 Along-track triplet of

images 1

7 EROS –B1 Israel/ImageSat 25 Apr 2006 Pan 0.7 7*up to 21 Along –track Across-

track Variable

8 KOMPOSAT 2 Korea /KARI 28 July 2006 Pan 1 Multi 4 15 Across –track Variable

9 WorldView-1 USA/Digital Globe 18 Sep 2007

Pan (N)0.5 (20º off-N) 0.55 17.6*17.6 Along-track Variable

10 WorldView-2 USA/Digital Globe 8 Oct 2009

Pan 0.46 20º off-N) 0.52 48*110 Along -track Variable

11 GeoEye-1 USA/GeoEye 6 Sep 2008

Pan (N) 0.5 Multi(N) 2

Pansharpened

15.2 area 224*28 Along-track Variable

Case study for IKONOS

Six Ikonos images (four on one track and two on another track) were collected for a test site at

Tampa Bay, Florida, in 2007.

Different combinations of Ikonos stereo image pairs, both along-track and cross-track, were

formed. Using the high resolution satellite image processing system developed at the Ohio State

University,

GPS controlled ground control points, and a number of check points were used, average errors of

these determined GPS points are 0.014 m in the X direction (easting), 0.017 m in the Y direction

(northing), and 0.028 m in the Z (vertical) direction.

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0

45

90

135

180

225

270

315

Azimuth Angle(degree)

90 70 60 5080

Elevation Angle (degree)

1

2

3

4

5

6

4 new images

2 existing images

Orbital positions of the new and existingIkonos images in an azimuth-elevation diagram.

Rongxing et al. (2009)

Stereo image from satellite can be capture by two way: 1. Cross track – in figure 1&5 images produce

cross track stereo pair. Image quality may affected due to time lag (revisit time) in two imaging.

2. Along track – in figure 1&2 images produce along track stereo pair. Here time lag is negligible.

Continue.. Data Set 1

new images )(4

Data Set 2

) existing images(2

Stereo image pair

combinations6

)along track(

GCPs, 13 CKPs2

RMSE by Check points

Stereo image pair

combinations6

)across track(

2 GCPs, 6 CKPs

RMSE by Check points

Translation model Translation model

Accuracy Assessment

Data processing flow chart for geopositioning

accuracy analysis.

ID ImagesConvergence

Angle (di)δx δy δz

1 2 and 3 12.311° 0.511 1.506 2.949

2 1 and 2 15.210° 0.568 1.454 2.362

3 3 and 4 17.691° 0.768 1.151 2.321

4 1 and 3 27.521° 0.445 1.392 1.895

5 2 and 4 30.002° 0.554 0.980 1.502

6 1 and 4 45.212° 0.525 1.055 0.691

ID ImagesConvergence

Angle (di)δx δy δz

1 1 and 5 15.635° 0.618 1.173 1.895

2 2 and 5 18.018° 0.446 1.186 1.908

3 3 and 6 18.954° 0.682 0.757 2.231

4 3 and 5 26.906° 0.799 0.946 1.855

5 1 and 6 39.484° 0.657 0.395 1.288

6 4 and 5 42.576° 0.699 0.827 1.038

Rongxing et al. (2009)

Along track RMSE Cross track RMSE

Conclusion

The convergence angle plays an important role in along-track or cross-track stereo mapping, especially in improvement of the accuracy in the vertical direction;

Regardless of stereo configuration (along-track or cross-track), the accuracy in the X (cross-track) direction is better than that in the Y (along-track) direction;

Although there is a slight correlation between the convergence angle and the accuracy in the Y (along-track) direction in the case of along-track stereo configuration, no distinct relationship is found in the X (cross-rack) direction.Similarly, improvement of the horizontal accuracies is foundwith increased convergence angles when dealing with crosstrackstereo pairs.

Literature citedDeilami K., and Hashim M. (2011). “Very High Resolution Optical Satellites for DEM Generation: A Review”, European Journal of Scientific Research ISSN 1450-216X, Vol. 49, No.4, pp. 542-554.

G. (2003). “Block adjustment of high-resolution satellite images described by rational polynomials”, Photogrammetric Engineering and Remote Sensing, Vol. 69 (1), pp. 59-68.

Kramer H.J. (2002). “Observations of the Earth and its environment: survey of missions and sensors”, Springer, Berlin Germany.

Rongxing Li, Xutong Niu, Chun Liu, Bo Wu, and Sagar Deshpande (2009) “Impact of Imaging Geometr y on 3DGeopositioning Accuracy of Stereo Ikonos Imagery, American Society for Photogrammetry and Remote Sensing, pp. 1119-1125.

Vassilopouloua S., Hurnia L., Dietrichb V., Baltsaviasc E., Paterakic M., Lagiosd E., and Parcharidis I. (2002). “Orthophoto generation using IKONOS imagery and high-resolution DEM: a case study on volcanic hazard monitoring of Nisyros Island (Greece)”, ISPRS Journal of Photogrammetry & Remote Sensing, Vol. 57, pp. 24– 38.

Zhilin L., Qing Z. and Christopher G (2004), Digital Terrain Modelling principle and methodology, CRC Press, London.

Thank you

Stereo image acquisition Stereo images acquire for extracting the DEM information

Aerial platform

Analog camera

Digital camera

Digital camera

Digital camera gaining popularity due its property of digitally recording image.

Increasing capability provide many option :

Frame sensor concept vs line scanning approach

Multi-head head system vs single head sensor

Large image format vs medium or even small format camera

Panchromatic vs multispectral data recording

Integration with GPS and IMU devices to get directly geo-referenced image

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The GSD (ground sampling distance) for digital cameras is calculated with the followingformula:

GSD = Where hg = flying height above ground ck = focal length

Klaus J. (2008)

h g   x  CCD   pixel   size  c k

XA B - XA

A