Re: [Matplotlib-users] basemap UTM conversion discrepancy

[Stefan M. <in...@st...>]

Hi Jeff,

I'm not an expert in coordinate transformation and the usage of proj, so
I can't exactly tell you if I have all the datum files installed. If you
could tell me what files could be missing I could search for them.

What makes me wonder, is that you get the results that my
mpl_toolkits.basemap.pyproj.Proj usage produced. When using some
conversion tools on the internet like
http://home.hiwaay.net/~taylorc/toolbox/geodesy/datumtrans/ or
http://www.uwgb.edu/dutchs/UsefulData/ConvertUTMNoOZ.HTM
I get the results that my commandline proj produces.
So I think that something with my pyproj installation is not working.

Regards,
   Stefan.

Am Montag, den 19.12.2011, 15:51 -0700 schrieb Jeff Whitaker: 
> On 12/19/11 2:23 PM, Stefan Mertl wrote:
> > Hello,
> >
> > I'm starting to use the mpl_toolkits.basemap.pyproj.Proj class to do
> > lon/lat to UTM coordinate conversion.
> > I did some tests and noticed that there is a discrepancy between the
> > mpl_toolkits.basemap.pyproj.Proj output and the proj commandline tool
> > output.
> >
> > e.g.: I'm converting the coordinates lat=48.2; lon=16.5 to UTM
> > coordinates UTM zone 33 with WGS84 ellipse.
> > I'm using the following proj4 string for the conversion:
> > +proj=utm +zone=33 +ellps=WGS84 +datum=WGS84 +units=m +no_defs
> >
> > The output using mpl_toolkits.basemap.pyproj.Proj is:
> > x: 611458.865;  y: 5339596.032
> >
> > The proj commandline tool using the same proj4 string gives:
> > x: 611458.69 y: 5339617.54
> >
> > As you can see, the y coordinate differs significantly.
> >
> > Here's the code used with the basemap pyproy classes:
> >
> > --------------------------------------------------
> >
> > from mpl_toolkits.basemap.pyproj import Proj
> >
> > # I got the proj string from
> > # http://spatialreference.org/ref/epsg/32633
> > myProj = Proj("+proj=utm +zone=33 +ellps=WGS84 +datum=WGS84 +units=m
> > +no_defs")
> >
> > lat = 48.2
> > lon = 16.5
> >
> > (x,y) = myProj(lon, lat)
> >
> > print "x: %.3f; y: %.3f" % (x,y)
> >
> > ---------------------------------------------------
> >
> > Can somebody explain me this behavior?
> >
> > Regards,
> >     Stefan.
> >
> Stefan:
> 
> When I run this test, I get the same answer with both, and it is the 
> same as the answer basemap.pyproj gave you.  I suspect you didn't 
> install the extra datum files with your command-line proj distribution.
> 
> -Jeff
>