[mapserver-users] Projection help: proj command line

[Dirk Jesko]

Hi Matthew,

try cs2cs instead of proj, e.g.

cs2cs +init=epsg:26915 +to +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 
+lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs


With proj you have to do the inverse projection from epsg:26915 (your 
from projection) to latlon/wgs84 (epsg:4326) first,

proj -I -f "%.8f" +init=epsg:26915

In a second step project the resulting latlon coordinate into your 
to-projection:

proj -f "%.4f" +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 
+x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs

Both version should work. Just for comparison, I got the following 
result for the first point of your extent:

epsg:26915        : 184056.505, 4809728.25
epsg:4326         : -96.89976708 43.37391004
your to projection: -10786832.7293 5369059.0540

I hope, that this is correct and will help.

Dirk


> Hi,
>
> This question is tangential to Mapserver, but critical to me
> nonetheless.  I'm trying to reproject a shapefile in a mapfile from
>
> =========================================================
> PROJECTION
>     "init=epsg:26915"
> END
> =========================================================
>
> to
>
> =========================================================
> PROJECTION
> 	"+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0
> +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs"
> END
> =========================================================
>
> my extent in the 'from' projection are:
>
> =========================================================
> EXTENT      184056.505 4809728.25 767381.245 5478975.75
> =========================================================
>
> Can someone help me figure out what my EXTENT should be in my 'to'
> projection?  I've tried the following extents derived from the 'proj'
> command line outputs as extents, but was not successful:
>
> =========================================================
> $ proj -I -f "%.4f" +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0
> +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null
> +wktext  +no_defs
> 184056.505 4809728.25
> 1.6534  39.6121
> 767381.245 5478975.75
> 6.8935  44.0874
>
> $ proj -I -f "%.4f" +init=epsg:26915
> 184056.505 4809728.25
> -96.8998        43.3739
> 767381.245 5478975.75
> -89.3140        49.4047
> =========================================================
>
> Anybody have any ideas what I am doing wrong?  Do I somehow have to
> chain projections together to get from my 'from' projection to my 'to'
> projection?
>
> Thanks,
> Matt
>
> --
> It is from the wellspring of our despair and the places that we are
> broken that we come to repair the world.
> -- Murray Waas
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