Relative DEM Production from SPOT Stereo without GCP
ASkihito Akutsu, Ryutaro Tateishi
Remote Sensing & Image Research Center, Chiba University
1-33 Yayoi-cho, Chiba 260 Japan
Abstract
The authors propose a practical method to produce relative DEM (digital elevation model) from SPOT level 1A stereo pair ore triplet images without using GCP (ground control points). Proposed method consists of 1) stereo matching by correlation, 2) calculation of an intersecting point of viewing lines by using satellite geometric data and 3) interpolation of random data to grid data. Proposed stereo matching technique is based on selection of target points by preprocessing of edge detection, search along approximate epipolar line and multi window matching. RMS of relative error of produced DEM with a grids of 25 meter was found to be less than 25 meter compared with a topographic map with a scale of 1:2:500. This relative error includes error by interpolation and errors by mismatched points. Therefore it is expected to improve the relative accuracy more after removing these errors.
Introductiuon
Since SPOT/HRV stereo data were provided, there were many papers on DEM production using SPOT digital data. These papers mainly consisted of two parts: (i) matching technique and (ii) generation of digital elevation model. The matching technique has generally been done by template correlation method. Recently the least-square matching method has presented by Forstner (1982) [1]. Rosenhoilm, D. (1988) [2] reported the application of least-square method to SPOT stereo image data. But the least-square method is effective only when accurate matching which in a pixel is necessary. Concerning with the matching technique using the correlation method, many investigations were done. Hattori, S. et al (1986) {3} reported the multi-step correlation method known as coarse-to-fine technique. In general, DEM was generated by obtaining parallaxes. To obtain parallaxes from satellite stereo images, image data should be rectified into epipolar aligned format. Otto, G.P. (1988) [4]showed that SPOT data could not be rectified into an exact "epipolar aligned" format without a DEM. Tateishi, R. et al (1988) [5] reported another method to obtain three dimensional coordinates of matched points by the calculation of an intersecting point of viewing lines which are derived from satellite geometric data and coordinate of matched point.
This paper proposes a practical method to produce relative DEM from SPOT level. 1A stereo pair or triplet images in the area where GCP are not available. The matching method is based on correlation technique. To calculate the matching points efficiently, the target points on one image are selected by edge detection and search area on the other image is determined by approximate epipolar line and maximum slope gradient. To eliminate mismatching, multiwindow matching (11 by 11, 15 by 15 and 29 by 29 pixels window matrices) is applied in the paper. Elevation of matched point is derived by the above method by Tateishi {%}. The grid elevation data are calculated from random DEM data using weighted mean interpolation. RMS of relative error of produced DEM is calculated by comparing with a topographic map with a scale of 1:2,500.
Spot Image
The Stereo Triplet Images Covered Mt. Fuji in Japan was used in this study. The parameters of three images are as follows:
| |
|
'Left image' 'Center image' |
'right image' |
| Spectral mode |
: |
Panchromatic Panchromatic |
Panchromatic |
| Senaor |
: |
HRVI HRVI |
Panchromatic |
| Observation Data |
: |
March 17 1986 March 7 1986 |
March 8 1986 |
| Viewing angle |
: |
15.4 degree 4.3 degree |
23.8 degree |
| |
|
East East |
West |
| Processing level |
: |
1A 1A |
1A |
| Path-row |
: |
329-279 329-279 |
329-279 |
The test area is Turu City near Mt. Fuji which includes 256 by 400 pixels. (Figure 5.)
