Support derived SRS/GeoTransform in VRT

[whardier]

This is a long outstanding feature I am looking forward to. I have had to create XML reprocessing scripts to handle this functionality for me.

The Problem:

The problem isn't that there is a problem, it's that there is a much faster and more efficient method of doing mass image processing with advanced features by using symlinks and VRT templates. Creating an image composite directory containing symlinks to source imagery as specifically named files ('band1.tif', 'espa_sr.tif', 'etc...') which point to the original source files allows me the ability to simply place a VRT file in the directory which contains colortable overrides, different band compositions, complex value scaling and mask generation bands. All without writing a single line of Python (Python is 150% of what I use for this anyways and I have an appreciation for letting C libs handle array processing)

Unfortunately I can't simply put a VRT into place and have it know the SRS/GeoTransform parameters. I have to put it into place and scan the source images I am using with a custom VRT updater script/function in order to determine extents and transformation.

The Solution:

Keeping in mind that VRT is a standard to a good degree and cross platform/framework. It would be very interesting indeed to add some flags to GDAL like VRT_SRS_FROM_BAND=(band_number) and VRT_GEOTRANSFORM_FROM_BAND=(band_number) and then continue processing the VRT with a binary or library call. What may end up working out really well however is adding some fields to some blank SRS and GeoTransform elements.

<SRS use_bands='1, 2, 3, 4'></SRS>

<GeoTransform use_bands='1, 2, 3, 4, 5, 6' extend_bounds='1'></GeoTransform>

Thoughts/Concerns ?

[Even Rouault]

Not sure about what the VRT would be when multiple bands are specified in use_bands in case they have contradictory information. More fundamentally, VRT bands can have many sources in them, not just one, so guessing SRS / GeoTransform would be ambiguous.

[whardier]

I believe when multiple VRTRasterBand are referenced there would be an attempt to use majority information and expand bounding boxes accordingly.

In the case where a single VRTRasterBand has multiple sources similar rules for expanding the bounding box based on a preference should be available.

I hope this is worth consideration.

[Even Rouault]

This ticket has been automatically closed because Trac is no longer used for GDAL bug tracking, since the project has migrated to GitHub. If you believe this ticket is still valid, you may file it to ​https://github.com/OSGeo/gdal/issues if it is not already reported there.