[FWTools] gdal_merge with nodata value

[Bryan Keith]

Frank Warmerdam wrote:
> Bryan Keith wrote:
>> So I gave up on Windows and tried on linux with an old version of 
>> FWTools (1.0.0a7) and an old version of gdal_merge.py (Revision 1.21), 
>> and I got the same memory error that I ended up with on windows (albeit 
>> much more quickly).  Now I'm thinking that specifying the nodata flag 
>> does indeed use much more memory than without it and that I'll have to 
>> bump up available memory to get these files to process.
> 
> Bryan,
> 
> The gdal_merge.py script does load the entire source image into memory.
> If you use nodata values, it also creates multiple copies in memory as
> it does the various operations.  So gdal_merge.py is really only appropriate
> for modest sized input files.
> 
> Ideally you should be using gdalwarp.  It supports nodata values, can handle
> a bunch of input files at once, and should not suffer these memory problems.
> 
> Unfortunately the arguments are non-trivially different than gdal_merge.py,
> so you may need to do some fiddling about.
> 
> Best regards,

Frank,

Thank you.  That did the trick. gdalwarp took a while to run, but there 
were no memory problems.

Bryan