[Gdal-dev] reprojecting 2.0

[Paul Kelly]

Hello Maciek

On Sat, 26 Jun 2004, Maciek Sieczka wrote:

> in the another system. Is it now possible to derive exactly the original
> raster A from the raster B back, or, if not, how do I proceed to derive it
> back possibly unchanged?

I would say the short answer is you can't, because re-projecting involves 
resampling the raster and you will lose information through interpolation 
(or shifting pixel centroids if using nearest neighbour resampling). The 
GRASS r.proj man page has quite a good explanation of this:
http://www.geog.uni-hannover.de/grass/gdp/html_grass5/html/r.proj.html

Maybe to give yourself more control over the process convert the raster 
into sites (GRASS r.to.sites) before re-projecting and then use your 
preferred interpolation method (appropriate for your data) to create your 
new raster from the re-projected sites.

Doing this in GRASS gives you more control over 
the process but forces you to think in detail about what you are doing, 
whilst gdalwarp is very good if you want the job done quickly without 
having to think too much about it (or if you already understand the 
algorithms it uses and know they are appropriate for your purpose).

Paul