DEM Generation using JERSI OPS Stereo Data
2.2 Stereo Matching
The stereo matching were carried out by using the area correlation method on the two phases.
The approximate matching was carried out using the low frequencies images in the first phase. The low frequencies images were the two value images transformed by the difference from the original image to the local average.
The detail matching was carried out using the high frequencies images in the second phase. The high frequencies images were the enhanced images by added the difference from the original image to the local average. The next equation shows the calculation of the average.
Where :
p(x, y) : original image value
m(x, y) : local average
N : window size for local average
the first phase : 25 - 35 the second phase 19: - 15
The neighborhood of matching point detected in the first phase were researched using the correlation window.
This method has the advantage that the size of correlation window is more smaller than other method, so that the computation time is reduced.
3 Generation of DEM
3.1 Test site
The test site is shown in table 2
Table 2 Test Site
| |
Band3 ( nadir ) |
Band 4 ( forward ) |
| GRS |
78 - 248 |
78 - 246 |
| Observation Date |
March 18, 1993 |
March 18, 1993 |
| Processing Data Level |
Level 10 |
Level 10 |
| Gain Mode |
High Gain |
High Gain |
3.2 Evaluation for Generated
DEM
The 28 ground control points selected in the test site for the conparison the generated DEM with the ground control points.
These points were got the absolute elevation using 1/50,000 topographical map.
3.3 Results
The results of the generated DEM are shown in Table 3 and Fig. 2 the generated DEM had the offset with vias and the gain with trend by compared with GCPs.
Table 3 Calculation Accuracy of Elevation
| |
Positive Maximum Error (m) |
Negative Maximum Error (m) |
Ave. of Absolute Difference |
R.E.M.S. (m) |
Bias (m) |
Trend X Direction (m/pixel) |
Trend Y direction (m/line) |
no corre-
ction |
1159.2 |
0.0 |
1084.1 |
1084.8 |
1083.1 |
0.0303 |
0.0028 |
| bias |
75.1 |
-58.6 |
31.6 |
36.8 |
0.0 |
0.0303 |
0.0028 |
| bias and trend |
82.7 |
-53.5 |
22.8 |
30.0 |
0.0 |
0.0 |
0.0 |
| 1 pixel = 18.3m, 1 line = 24.2m |
Figure 2 Contour Lines Generated from JERS - 1 OPS Stereo Data (left) and Those of 1/200000 Map (right)
It's for this reson that the DEM were generated by orientation without GCP. Therefore the relative elevation error of DEM as well as the absolute error were evaluated.
The bias with offset was defined as the difference from the average of DEM to absolute elevation data. So the trend with gain was defined as the incline of plane, because it is assumed that DEM is inclined along a plane.
That plane is defined as follows.
Dhxy = aX + bY + c
Where :
Dhxy : the elevation error in the target point ( X, Y, )
a,b,c : coefficients are calculated by the method of least squares.
4. Conclusion
The absolute elevation error weren't got good accuracy. It's for this reson that the mis matching points were existed in the clout area and the orientation recorded in CCT hasn't so high accuracy. The orientation errors weren't still investigated. Therefore, the elevation error effected by the orientation error weren't also investigated.
However, the relative elevation accuracy are as same as the theoetical value that calculated by the ground resolution devided (B/H ratio)*2. [the theoretical value is 30.5 m - 40.3 m ] if some GCPs are got in the target area, the high accuracy DEM are generated b corrected the bias and the trens. But it isn't nessesary to go many GCPs.
The accuracy of generated DEM has the potentiality of drawing 1:200,000 scale topgraphic map.
Also it isn't nessesary to be operated by a man, Therefore DEM is generated automatically. It's useful to generated the DEM for global data.
Reference
-
Y. Mukai, T. Sugimura, K. Arai, Generation of DEM by the method of Correcting the Elevations of Ground Control Points using System Corrected SPOT Data, Vol.12, No.3, Journal of Remote Sensing Society of Japan, 1992
- Y. Mukia. T. Sugimura. H. Kimura. Early Evaluation of JERS-1 OPS Data and their Distribution, Vol.12, No.3, Journal of Remote Sensing Society of Japan, 1992.
- H. Hino, H. Ono, Development Status of JERS-1 Mission Equipment Initiaal Checkout of OPS, MDT and MDR, Vol.12, No.3, Journal of Remote Sensing Society of Japan, 1992
- S. Murai and Others, Analytical Photogrammetry, JSPRS, 1988
- S. Murai and R. Shibasaki, Automated Generation of Digital Terrain Model (D.T.M.) using Linear Array Sensor Data, Vol.23, No.3, Photogrammetry and Remote Sensing.
