8.22. SPOT5¶
SPOT5 is a CNES (Space Agency of France) satellite launched on May 2002 and decommissioned in March 2015. SPOT5 contained two High Resolution Stereoscopic (HRS) instruments with a ground resolution of 5 meters. These two cameras were pointed forwards and backwards, allowing capture of a stereo image pair in a single pass of the satellite.
ASP supports only images from the HRS sensors on SPOT5. These images
come in two parts, the data file (extension .bil
or .tif
) and
the header file the data file (extension .dim
). The data file can be
either a plain binary file with no header information or a GeoTIFF file.
The header file is a plain text XML file. When using SPOT5 images with
ASP tools, pass in the data file as the image file and the header file
as the camera model file.
All ASP tools can handle .bil
images (and also .bip
and .bsq
)
as long as a similarly named .dim
file exists that can be looked
up. The lookup succeeds if, for example, the .dim
and .bil
files differ only by extension (lower or upper case), or, as below,
when an IMAGERY.BIL file has a corresponding METADATA file.
A sample SPOT5 image can be found at at http://www.geo-airbusds.com/en/23-sample-imagery.
One issue to watch out for is that SPOT5 data typically comes in a
standard directory structure where the image and header files always
have the same name. The header (camera model) files cannot be passed
into the bundle_adjust
tool with the same file name even if they are
in different folders. A simple workaround is to create symbolic links to
the original header files with different names:
ln -s front/SEGMT01/METADATA.DIM front/SEGMT01/METADATA_FRONT.DIM
ln -s back/SEGMT01/METADATA.DIM back/SEGMT01/METADATA_BACK.DIM
bundle_adjust -t spot5 \
front/SEGMT01/IMAGERY.BIL back/SEGMT01/IMAGERY.BIL \
front/SEGMT01/METADATA_FRONT.DIM back/SEGMT01/METADATA_BACK.DIM \
-o ba_run/out
parallel_stereo -t spot5 \
front/SEGMT01/IMAGERY.BIL back/SEGMT01/IMAGERY.BIL \
front/SEGMT01/METADATA_FRONT.DIM back/SEGMT01/METADATA_BACK.DIM \
st_run/out --bundle-adjust-prefix ba_run/out
See Section 6 for a discussion about various speed-vs-quality choices of the stereo algorithms.
One can also mapproject the SPOT5 images before they are passed to
parallel_stereo
. In order to do so, you must first use the
add_spot_rpc
tool to generate an RPC model approximation of the
SPOT5 sensor model.
add_spot_rpc front/SEGMT01/METADATA.DIM -o front/SEGMT01/METADATA.DIM
add_spot_rpc back/SEGMT01/METADATA.DIM -o back/SEGMT01/METADATA.DIM
This will append the RPC model to the existing file. If the output is a separate file, only the RPC model will be saved to the new file.
Then use the spot5maprpc
session type when running parallel_stereo
on the mapprojected images. See the note in Section 6.1.7
about perhaps reducing the resolution of the DEM to mapproject onto if
ghosting artifacts are seen in the produced DEM.
mapproject --tr gridSize sample_dem.tif front/SEGMT01/IMAGERY.BIL \
front/SEGMT01/METADATA.DIM front_map_proj.tif -t rpc
mapproject --tr gridSize sample_dem.tif back/SEGMT01/IMAGERY.BIL \
back/SEGMT01/METADATA.DIM back_map_proj.tif -t rpc
parallel_stereo -t spot5maprpc front_map_proj.tif back_map_proj.tif \
front/SEGMT01/METADATA.DIM back/SEGMT01/METADATA.DIM \
st_run/out sample_dem.tif
Notice how we used the same resolution (option --tr
) for both
images when mapprojecting. That helps making the resulting images more
similar and reduces the processing time (Section 6.1.7.3).
See Section 6 for a discussion about various speed-vs-quality choices of the stereo algorithms.