[gdal-dev] Can I change SOURCE_EXTRA setting at compile time?

[Frank Warmerdam]

Roger André wrote:
> I've been mercilessly beating a dead horse on a couple of lists about 
> some weird artifacts that I'm getting when doing reprojections in 
> Mapserver from epsg:4326 to epsg:900913.  It's recently come to my 
> attention that something was discussed in an IRC chat that might be 
> pertinent to this issue, and I was hoping I could test it.  
> Specifically, it relates to SOURCE_EXTRA, and although the conversation 
> at the time dealt with issues at the International dateline, I think it 
> might also manifest itself in other edge cases (literal edges). ;).
> 
> I would like to know if it is possible to set SOURCE_EXTRA to something 
> other than 1 at compile time?  I do not see it listed as an option in 
> the configure documentation, but perhaps I could edit a file, or pass in 
> the flag anyhow?

Roger,

I haven't followed your problems closely (I recall something about datum
shifts).  The SOURCE_EXTRA only helps with the GDAL warper.  If you wanted
you could modify the following code in gdal/alg/gdalwarpoperation.cpp
and recompile:

/* -------------------------------------------------------------------- */
/*      Allow addition of extra sample pixels to source window to       */
/*      avoid missing pixels due to sampling error.  In fact,           */
/*      fallback to adding a bit to the window if any points failed     */
/*      to transform.                                                   */
/* -------------------------------------------------------------------- */
     if( CSLFetchNameValue( psOptions->papszWarpOptions,
                            "SOURCE_EXTRA" ) != NULL )
     {
         nResWinSize += atoi(
             CSLFetchNameValue( psOptions->papszWarpOptions, "SOURCE_EXTRA" ));
     }
     else if( nFailedCount > 0 )
         nResWinSize += 10;


Perhaps change the nResWinSize += 10 line to nResWinSize += 100 or something
like that.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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