[gdal-dev] seeking suggestions for pixel arithemtic programs

Mark Phillips mbp at geomtech.com
Tue Apr 20 08:15:02 EDT 2010


I have a collection of MODIS imagery files (in Erdas Imagine .img  format),
and I need to to be able to derive new files from them, where the derived
file has the same format and metadata as the input files, but each pixel in
the derived file file is some arithmetic function of the corresponding
pixels in the input files.  For example,

  derived_file_pixel(i,j) = average of pixel(i,j) for each input file

I'd like to set up a system for creating these derived files that makes it
easy to change the particular function (for example, compute the sum instead
of the average, or compute a difference, or a weighted average, etc etc),
and easy to change the set of input files.

I poked around in the GDAL documentation and it looks like one way to do
this would be to use a VRT with a pixel function, but it looks like that
would involve writing a program, either in C or in python.  I can do that,
but ultimately I'd like to set things up so that my
non-programmer colleagues can change the pixel function and generate new
derived files without having to get me to write a new program.

So, I'm wondering if there's a command-line utility program that can be used
for doing this kind of thing, that allows the pixel function to be given as
parameter on the command.  Either a program that's part of GDAL itself, or
part of some other package that uses GDAL?  I'd appreciate any suggestions.

Also, if I do end up writing the program myself using GDAL, does the VRT +
pixel function approach I described sound like the best way?  I know enough
about GDAL to feel pretty sure that it'd be good for doing this kind of
thing, but I've never actually written a program using GDAL, so I'd
appreciate any pointers.


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