[gdal-dev] The new WCS driver
ari.jolma at gmail.com
Thu Nov 16 11:50:17 PST 2017
I'm happy to suggest that
would be accepted into the GDAL trunk, thus to be included into the
coming version 2.3.
I'm not making a PL since the GDAL at github is not a primary source.
There is a python test program in the above directory (it should be
moved to autotest eventually but it's now there for easier access).
There are a couple of things that I've done:
1) Introduced "WCS:<URL>" syntax for the driver.
2) Introduced a cache for various XML files (GDA WCS service file, GDAL
metadata files, server responses).
3) Split the driver into a base class and version specific subclasses.
I have tested the driver with four real servers (ArcGIS, GeoServer,
MapServer, and Rasdaman) and it can work with all of them in all
versions they support. I have checked the responses (scaled and in CRS
with inverted axis order (except ArcGIS)) in QGIS and they are ok - not
always identical with each other but close enough. There is
documentation and test code - Perl code to run gdal_translate calls to
real servers and Python code to run tests against the responses obtained).
However, I assume there to be many small things in the code to
review/change. I find the typical GDAL code often difficult to read and
especially write. So I have written the code in a way that's easier for
me to work with. I think there could be more strict rules for writing
the code, and an automatic code checker (linter) would be useful.
Besides things that a linter would check, I find it useful to write and
debug shorter functions (max a screenful), while GDAL functions tend to
be long, which often make them hard for me to understand and follow.
Some issues specific to this work:
- I ended up writing quite many utility functions. Some may reinvent
- The initial call to the server returns a dataset with subdatasets but
without bands. It may be that opening a subdataset returns a dataset
without bands (there are more than 2 dimensions). Then the additional
subdataset metadata is added to the SUBDATASETS metadata domain.
- The idea is that the service file in the cache is maintained through
options, which is used to change values in the file. The current set of
options is expected to grow.
- I have not tested the more exotic features of the driver - especially
mapping the time dimension to bands etc. I hope I have not broken what
worked before. This is an area where more work is needed.
- The code compiles and the tests run ok in a new Linux machine.
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