[GRASSLIST:3325] Re: no false norting in tmerc projection

[Eric G. Miller]

On Mon, Mar 11, 2002 at 06:55:04PM +0100, Markus Herrchen wrote:
> Hi,
> I have a problem in the definition of the coordinate system.
> I created a new location and mapset with the following PROJ_INFO file:
> 
> name: Transverse Mercator
> datum: nad27
> dx: -22.000000
> dy: 157.000000
> dz: 176.000000
> proj: tmerc
> ellps: clark66
> a: 6378206.4000000004
> es: 0.0067686580
> f: 294.9786982000
> lat_0: 42.0000000000
> lon_0: -114.0000000000
> k_0: 0.9996000000
> x_0: 500000.0000000000
> 
> But i was unable to define a false northing (in my case of 100000.).
> I added by hand a last line with
> 
> y_0: 100000.0000000000

I believe this has been fixed for future versions.  The addition of
y_0 should be sufficient.

> but this didn't help. In fact, when i load an ARC/INFO grid file,
> by the help of r.in.gdal, the resulting y-coordinate is false:
> the false northing is ignored!
> Is this a bug in the tmerc projection?

Are you sure that the imported file didn't have a Y shift?  And are you
sure r.in.gdal actually imported the data relative to the coordinate
system, or was the data imported as XY pixels?  The projection
definition shouldn't have much impact on r.in.gdal, other than it checks
to see the input data source and location have matching definitions.

-- 
Eric G. Miller <egm2 at jps.net>