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

[ardi]

Thanks a lot for your advice, Nicolas!

ardi



On Thu, Jun 11, 2015 at 1:09 AM, Nicolas Cadieux
<nicolas.cadieux at archeotec.ca> wrote:
> 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]" <[hidden email]> 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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