Figure 4 Orthophoto of map sheet 1225 draped over the DTM (1.5x increased heights), seen from north
under 60° zenith angle
7. CONCLUSIONS
It has been shown that with Kratky’s strict
photogrammetric model for SPOT images an accuracy of
9 - 10 m in planimetry and 6 m in elevation can be
achieved. Remarkable is the improvement of the
elevation accuracy though point transfer by least squares
matching.
The PMFs are faster, equally accurate and easier to
implement than the strict transformations. Consequently
they are suitable for use in image matching and digital
orthophoto generation.
A very good approximation of the epipolar line can be
derived from the PMFs. The application of the SPOT
geometry reduce the search space to 1-D thus increasing
the success, reliability and speed of the image matching.
A orthophoto of one SPOT scene can be produced in only
15 min. to a subpixel accuracy (« 10 m). Attention should
be paid to the accumulation of rounding errors when
incremental updating is used.
8. ACKNOWLEDGEMENTS
The authors express their gratitude to the Bundesamt für
Landestopographie, Bern, Switzerland for providing the
SPOT images and DTM data.
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