[mapserver-users] Rewarping/Reprojection with GDAL and -wo EXTRA_SOURCE parameter

[Heiko Schröter]

Hello all,

we need to rewarp epsg:4326 to polar i.e. "+proj=ortho +over +lon_0=0 
+lat_0=90 +ellps=WGS84 +datum=WGS84 +units=m +no_defs" for satellite 
data projection.
The problem is that not enough data are read from the source raster 
image and the map is "cutout" at the poles.

gdalwarp can be passed a switch i.e. "-wo EXTRA_SOURCE=750", which gives 
the correct warped image on the commandline.

To make use of it in mapserver a hint has been given in an old mailing 
thread (sorry, lost the source) to adjust the following code snippet in 
resample.c:

Version: mapserver-6.4.0
resample.c
<snip>
/* -------------------------------------------------------------------- */
   /*      Project desired extents out by 2 pixels, and then strip 
to      */
   /*      available 
data.                                                 */
   /* 
-------------------------------------------------------------------- */
   memcpy( &sOrigSrcExtent, &sSrcExtent, sizeof(sSrcExtent) );
   sSrcExtent.minx = floor(sSrcExtent.minx-1.0);
   sSrcExtent.maxx = ceil (sSrcExtent.maxx+1.0);
   sSrcExtent.miny = floor(sSrcExtent.miny-1.0);
   sSrcExtent.maxy = ceil (sSrcExtent.maxy+1.0);
<snap>

Changing the -/+1.0 to -/+1250.0, for example, warps the RASTER image 
correctly.

Unfortunatly using POSTGIS layer or LINE type layer (i.e. for a grid) 
the reprojection is distorted as before for the RASTER layer.

Is there an option or a place in the sources where the POSTGIS or LINE 
data layers are handled so that a workaround as above for the RASTER 
Layer could be used ?

I could imagine that it would be a good idea to have a parameter 
"EXTRA_SOURCE" in the mapfile if need be for polar plots.

Thanks
Heiko