[Proj] [delphi proj api]: Setting up TCoordinateTranslator

Paul Kelly paul-grass at stjohnspoint.co.uk
Fri Mar 7 13:31:10 EST 2008

On Fri, 7 Mar 2008, Christian Kirchhoff wrote:

> Hello,
> I'd like to use the Delphi PROJ API to translate coordinates. The coordinates 
> come from GoogleMaps, thus are lat/lng values.
> I want to match them to shapes from a shape file which I can read with the 
> ShapeAPI. I have got the following information the the prj file of the shape:
> PROJCS["Germany_Zone_3",GEOGCS["GCS_Deutsches_Hauptdreiecksnetz",DATUM["D_Deutsches_Hauptdreiecksnetz",SPHEROID["Bessel_1841",6377397.155,299.1528128]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",3500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",9.0],PARAMETER["Scale_Factor",1.0],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]
> Therefore I thought that the TCoordinateTranslator I named "Proj" should be 
> opened with:
> Proj.Open('+proj=tmerc +ellps=bessel +lon_0=9 +x_0=3500000');
> ...but I am not very familiar/experienced yet.
> Anyway I have test coordinates from GoogleMaps, e.g. (50.1056069418592, 
> 8.404541015625). The region this coodinates lay in as exactly the region that 
> is covered by shapes in the shape file. The bounds of the shape file are, 
> according to what the ShapeAPI returned:
> ( 3394468.028, 5504381.719,0.00,0.00) to ( 3424916.697, 
> 5537463.422,0.00,0.00)
> But the translated Google coordinates are:
> 8451430,97 m, 1229074.77 m
> Which is totally elsewhere.
> My question is: Did I read the values from the shape's prj file wrong? Or did 
> I use the wrong parameters when setting up the TCoordinateTranslator?

I think you have passed the latitude and longitude values in the wrong 
order. It should be longitude first, followed by latitude. Here is quick 
test I did using your values and the cs2cs program that comes with PROJ.4:

cs2cs +proj=longlat +a=6377397.155 +rf=299.1528128 \
+towgs84=606.000,23.000,413.000 +to +proj=tmerc +lat_0=0 +lon_0=9 \
+k=1 +x_0=3500000 +y_0=0 +no_defs +a=6377397.155 +rf=299.1528128 \
+towgs84=606.000,23.000,413.000 +to_meter=1
8.404541015625 50.1056069418592
3457407.04      5552194.69 0.00
50.1056069418592 8.404541015625
8451430.97      1229074.77 0.00

Best regards,


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