[Proj] Custom projection wildly inaccurate

[Oscar van Vlijmen]

> From: "Thy, Kristian"
> Date: Sat, 18 Nov 2006 01:17:16 +0100
> Subject: [Proj] Custom projection wildly inaccurate

 > I'm trying to reproject data in an obsolete Danish orthogonal projection
> called System34 in MapServer. To this end, I've found a .prj file for ArcMap
> distributed by the Danish National Survey & Cadastre, which defines the
> following parameters:
....
 
> Problem is that this transposes the data many kilometres north and slightly
> west (and perhaps also distorts it slightly, I'm not sure). The effect can be
> seen in these three maps:
...

Another problem is that System 34 is not coupled to any projection. I have
heard of a transverse mercator approximation, but an orthographic?
The Danish use a 11th (13th?) degree polynomial to convert System 34
coordinates to UTM. I haven't seen this polynomial roaming on the internet,
so I cannot comment on the accuracy of approximations.
There are 3 zones in System 34 and the coordinate system is west-oriented.

Kort & Matrikelstyrelsen - Mere om System 34
<http://www.kms.dk/Referencenetogopmaaling/Referencesystemer/System_34/mere_
om_system34.htm>
On-line transformations:
<http://valdemar.kms.dk/trf/>