Il steps can be run in
luster complex were
creates
set of satellite images,
omputes orthoimages
ges or cloud areas,
er stitching of
orthomosaic
iciency of this fully
er day for GeoEye,
ow good efficiency
lware-software
PRESSE RE
previous section are
ers. We will give
to increase the quality
processing.
'S. We use the
ines: the whole area
rlapping image
the diagram’s edges
st junction of the
y function that
es, their
For each edge the
lic programming
penalty function for
lyline L, such that
L from the starting
:thod can be
er flood”. The
rithm. The
lel considering of
Figure 6. Automatic cut lines creation
If the images contain clouds a special module is used for their
automatic detection. This algorithm includes a successive
filtering of pixels — by intensity, deviation from the grey color,
dispersion and heterogeneity. The last function measures the
difference between changing of intensity along each axis and its
variation. At the last step the remaining pixels are composed in
components and their boundaries are calculated as polygons.
Figure 8. Cut lines around clouds and ortho mosaic without
clouds (no colour balancing for better visualization)
One of the unique algorithms we use to make ortho mosaics
look better is the usage of tie points that are calculated along cut
lines using standard cross-correlation algorithm. The images can
be stitched by a limited predefined value using these tie points
to eliminate discrepancies along seams (cut lines) as illustrated
on the following picture.
Figure 9. Tie points to eliminate residual discrepancies along
cut lines
5. CONCLUSION
Orthophoto production from VHR and HR sensors using RPC
and precomputed DEM can be effectively run on specialized
computer clusters with good scalability in fully automatic mode.
A special adaptation of algorithms and software is needed for
cluster environment. These algorithms are implemented in
PHOTOMOD HPC Edition DPW. The developed algorithms
are now extended for distributed GPU processing in cluster
environments, for DTM computing and filtering, for special
control function allowing to share the cluster between several
workgroups. The software module for integration with GIS
systems, databases and geoportals is also developed.
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