[gdal-dev] how to pick the correct projection

[Djordje Spasic]

Once again, thank you for the help Even.

What happens if the source raster spreads across two UTM zones? Which one should I pick then? Here is an example (the blue rectangle is the raster region):
https://www.dropbox.com/s/hbn4yqx3ool7j98/raster_two_UTMzones.jpg?dl=0

I intend to download rasters with the following size: 50x50km, 100x100km, 200x200, and 400x400km in length x width.

Regards,
Djordje Spasic

      From: Even Rouault <even.rouault at spatialys.com>
 To: Djordje Spasic <issworld2000 at yahoo.com> 
Cc: "gdal-dev at lists.osgeo.org" <gdal-dev at lists.osgeo.org>
 Sent: Wednesday, December 9, 2015 9:54 PM
 Subject: Re: [gdal-dev] how to pick the correct projection
   
Le mercredi 09 décembre 2015 20:55:53, Djordje Spasic a écrit :
> Thank you for the reply Even.
> 
> Based on your equation one can identify the UTM zone. Which in this case
> for Barcelona is: 31.
> 
> How can I identify the EPSG projection based on UTM zone 31?Is it possible
> to identify it with some formula too?

Add 32600 to the UTM zone for the northern hemisphere, or 32700 for the 
southern hemisphere.



> 
> Kind regards,
> Djordje Spasic
> 
> 
>      From: Even Rouault <even.rouault at spatialys.com>
>  To: gdal-dev at lists.osgeo.org; Djordje Spasic <issworld2000 at yahoo.com>
>  Sent: Wednesday, December 9, 2015 7:43 PM
>  Subject: Re: [gdal-dev] how to pick the correct projection
> 
> Le mercredi 09 décembre 2015 19:23:16, Djordje Spasic a écrit :
> > Hi,
> > 
> > I am downloading an open source .asc elevation files from
> > opentopography.org.​ I attached one of them in this email. Once
> > downloaded .asc elevation file need to be projected from WGS84 datum
> > (EPSG 4326) to Universal Transverse Mercator. Here is an example of how
> > this looks like in python GDAL for Barcelona Spain downloaded elevation
> > model: gdalwarp -s_srs EPSG:4326 -t_srs EPSG:32631 -r cubic
> > BarcelonaWGS84.asc
> > projectedToUTM.tif ​So in this case the EPSG:32631 has been used as a
> > projection (it hasn't been picked by me), it was googled.
> > 
> > But how do I know which projection to pick, depending on the location for
> > which the elevation data is downloaded? I googled a bit, and there are
> > few articles online, which suggest picking the right EPSG projection
> > based on UTM zone to which the downloaded elevation model belong
> > to:https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate
> > _ system#/media/File:Utm-zones.jpg
> > 
> > But I am not sure I understand how to choose the EPSG projection based on
> > UTM zone.
> > 
> > How can this be done?
> 
> Formula given in
> http://stackoverflow.com/questions/9186496/determining-utm-zone-to-convert-
> from-longitude-latitude
> 
> long2UTM <- function(long) {
>    (floor((long + 180)/6) %% 60) + 1
> }
> 
> Take the longitude of the central point of the source raster as input
> 
> Just thinking it could be interesting to have gdalwarp accept -t_srs
> AUTO:42001 to do that automatically:
> http://cite.opengeospatial.org/OGCTestData/wms/1.1.1/spec/wms1.1.1.html#au
> to_projections.42001
> 
> > Thank you for the reply.
> > 
> > Kind regards,
> > Djordje Spasic

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