zero vs null

[Zenon Panoussis]

Rahkonen Jukka wrote:

> Reprojecting images one to one tends to give you those black 
> edges because the original image boundaries does not match 
> exactly the dimensions of pixels in the reprojected image. 
> [...] a better approach to mosaic the original images before
> reprojection. If the original image is large enough to contain 
> the resulting, reprojected image totally within its extents then 
> the reprojected image will have no black pixels. Original images 
> does not need to be mosaiced physically but an image catalogue, 
> virtual layer, or how do you want to call can be used instead.  
> If gdalwarp is to be used then GDAL/VRT virtual raster layer 
> would is good for image source format.  So your work chain would 
> have one more step: after adding projection make a GDAL/VRT with 
> a gdal_merge.py script modified for this purpose, and reproject 
> and split that VRT layer to given extents by using gdalwarp with 
> "-te" switch. 

That looks like a better workaround than the one I'm currently using,
thanks. But should I also understand your reply to mean that there is
no way of telling gdalwarp to use NULL instead of 0 for the missing
pixels in a 1:1 reprojection?

Z