[Proj] Custom projection wildly inaccurate

Thy, Kristian Kristian.Thy at atkinsglobal.com
Fri Nov 17 19:17:16 EST 2006

Hi list,
(Apologies for sending HTML email - I'm stuck on OWA ...)
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:
PROJCS["Approximation of non-projective System 34 Sjælland",
      DATUM["D_WGS_1984", SPHEROID["WGS_1984",6378137.0,298.257223563]],
To get MapServer to reproject my data, I added the following code to ms4w\proj\nad\epsg:
<34005> +proj=ortho +lat_0=55.29235 +lon_0=12.105661 +x_0=-100000.0 +y_0=100000.0
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:
All three maps are drawn in EPSG:32632. The green line data is natively EPSG:32632. The blue points are fetched from a WMS service in EPSG:4326, EPSG:32632 and my custom transformation respectively. The difference between lat/lon and UTM is noticeable but acceptable, but my own projection is way off. I have confirmed the distortion with different data sources in System 34 - this WMS and an orthophoto from another source - so I'm certain the error is on my end. Can anybody tell me which rookie mistake I've commited? ;-)
best regards,
Kristian Thy

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