[Qgis-user] Do I need satellite raster layers relative to an extended UTM zone?

[Nicolas Cadieux]

Hi, 
It's never a good idea to delete files that you have reprojected.  Reprojection will, in most cases slightly alter the data although that depends on the parameters used.  You could always test by reprojecting the file back to the original projection and then by using raster math to see the differences, if any. 
If you want to save space, I suggest you compress the data using "deflate" parameters.  (You need to manually add support for bigtiff if the file is over 4GB. ) Once you are done, you can always do raster math to make sure data has not changed.  ( original layer - new layer should give zeros). 
For your second question, that is just the way it is! Since QGIS is open source, not ever programmer puts reprojection in their code. 
Cheers. 
Nicolas Cadieux M.Sc. 
Les Entreprises Archéotec inc.  
8548, rue Saint-Denis Montréal H2P 2H2 
Téléphone: 514.381.5112  Fax: 514.381.4995 
www.archeotec.ca 
On Jun 10, 2015 4:36 PM, "ardi [via OSGeo.org]" <ml-node+s1560n5210266h7 at n6.nabble.com> wrote: 

	Hi,
I've a satellite photo data set which spans across three UTM zones,
and I need to do some tasks in all three zones at once. Each image
tile from the data set is provided in two versions: one is projected
in the UTM coordinate system for the zone it actually belongs. The
other is projected over the central UTM zone, extending such central
zone.
AFAIK, QGIS can deal with layers belonging to different UTM zones,
because you see a lat/long display and layers are reprojected to
lat/long on the fly.
My question is: can I save disk space by storing the image tiles in
just one version, the version projected in its real UTM zone? Or would
I also need the versions projected into the (extended) central UTM
zone?
Just out of curiosity, what's the use of the version projected into
the extended zone? Is it because some GIS packages don't support
on-the-fly reprojection? Or why?
Thank you in advance
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