[Proj] Coordinate transformation assistance

[Bjørn Krangnes]

I am trying to convert from ITM to IG using EPSG codes but when trying to
initialize with the EPSG codes (ITM=2157 and IG=29903) I get error code 6.

The ITM has the following definition:

<2157> +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=0.999820 +x_0=600000
+y_0=750000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs  <>

IG has the following definition:

<29903> +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=1.000035 +x_0=200000
+y_0=250000 +a=6377340.189 +b=6356034.447938534 +units=m +no_defs  <>

These definitions I have found in a file with name EPSG downloaded from
the proj-4.50 project.

Bjørn

> On Thu, 12 Apr 2007, [iso-8859-15] Bjørn Krangnes wrote:
>
>> Hi,
>>
>> I am trying to go from Irish Transverse Mercator to IrishGrid75 Ireland
>> using GDAL C# and EPSG codes.
>>
>> The code is like this:
>>
>>
>>            double[] xyz = new double[3];
>>
>>            OGR.SpatialReference inp = new OGR.SpatialReference(null);
>>            OGR.SpatialReference outp = new OGR.SpatialReference(null);
>>
>>
>>            int stat1 = inp.ImportFromEPSG(2157);   // Irish Transverse
>> Mercator
>>            int stat2 = outp.ImportFromEPSG(29903); // IrishGrid75
>> Ireland
>>
>>            OGR.CoordinateTransformation tra = new
>> OGR.CoordinateTransformation(inp, outp);
>>
>>            xyz[0] = 600000.0;
>>            xyz[1] = 700000.0;
>>            xyz[2] = 22.22;
>>
>>            tra.TransformPoint(xyz);
>>
>> I think the problems is with ImportFromEPSG because both istat1 and
>> istat2
>> is 6 after execution. How to initialize the EPSG codes ?
>
> What is the problem?
> (Sorry I can't help with C-sharp stuff anyway but here's something else
> that may be important:)
> Those codes should work but to be clearer about what you're doing it is
> more obvious to enter the projection in PROJ.4 syntax IMHO. In particular,
> Irish Transverse Mercator uses the WGS84 ellipsoid while Irish Grid uses
> the Modified Airy, so you will need some datum transformation parameters
> with the Irish Grid projection to get an accurate transformation. I
> suggest:
>
> +proj=tmerc +lat_0=53.5 +lon_0=-8 +k=1.000035 +x_0=200000 +y_0=250000 \
> +no_defs +a=6377340.189 +rf=299.3249646 \
> +towgs84=482.530,-130.596,564.557,-1.042,-0.214,-0.631,8.15 +to_meter=1
>
> Those parameters are published by both Ordnance Surveys (ROI & NI) as
> having an accuracy of approx. 0.4m throughout Ireland.
>
> Interesting anyway; I didn't know anybody was actually using Irish
> Transverse Mercator for anything yet!
>
> Paul
>
>>
>> I am resending this request beacuse I have not had any feedback on my
>> previous request.
>>
>> Regards
>>
>> Bjørn Krangnes
>> Devonor AS
>> Telephone: +47 32 29 96 90
>> Direct Line: +47 32 29 96 91
>> Mobile: +47 45035640
>> E-mail: bkr at devonor.com
>> Web: www.devonor.com
>>
>>
>> _______________________________________________
>> Proj mailing list
>> Proj at lists.maptools.org
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>>


Bjørn Krangnes
Devonor AS
Telephone: +47 32 29 96 90
Direct Line: +47 32 29 96 91
Mobile: +47 45035640
E-mail: bkr at devonor.com
Web: www.devonor.com