[Proj] Coordinate transformation from meters to longitude/latitude

Frank Warmerdam warmerdam at pobox.com
Tue Jan 23 11:27:07 EST 2007

Yuriy Rusinov wrote:
> Hello !
> I want to transform some cartesian coordinates from its own projection
> invproj +proj=tmerc +lat_0=0 +lon_0=38.99999952571766 +k=1.000000 +x_0=0 
> +y_0=0 +ellps=WGS84 +units=m +no_defs
> 7.41094e+06 6.16614e+06
> Results are
> 135d51'17.113"W 234d40'40.974"N
> These data exceeds latitude limits and no errors, no asterisks in 
> output. Is this error and where it can be contains ?  Any ideas ? Thanks 
> in advance.


I see the same result.  I must confess to not understanding the math
involved, but Transverse Mercator is a projection without a well
defined boundary at which it becomes invalid.  Instead as you go further
and further from the central meridian things become more distorted and
bizarre effects accumulate.  And 7 million meters east of the central
meridian is a *long* ways.

I think the lesson is that you can't just throw locations several million
meters from the central meridian into TM and expect meaningful results.
But worse, the projection itself has no way of indicating it's reduced

Hopefully Gerald will give a less "black box" oriented answer.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

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