[gdal-dev] Confused about datum transformations

[dev4cx4m9z at snkmail.com]

Thanks for all the suggestions – they have given me many possibilities to eliminate, but I still haven’t really got an answer to the original question.

 

Am I required to have proj.dll built with support for the datums/projections I want to use, or is it sufficient to set GDAL_DATA such that gcs.csv and pcs.csv are visible? I’m working in VB.NET, and I’m not confident I can rebuild PROJ with the required datums, so I wish to avoid if possible. I’d even be prepared to use SetGeogCS explicitly as I only use a few datums. If I use SetGeogCS, I can’t see what purpose proj.dll serves.

 

I have set GDAL_DATA to the correct folder.

I have checked that the datum numbers I use are in the gcs.csv file.

 

From: gdal-dev-bounces at lists.osgeo.org [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of dev4cx4m9z at snkmail.com
Sent: Tuesday, October 18, 2011 4:12 AM
To: gdal-dev at lists.osgeo.org
Subject: RE: [gdal-dev] Confused about datum transformations

 

I’m not sure the code will help too much, but here are the relevant code fragments. I’m using a hand crafted VB.net wrapper which explains some of the syntax

 

Private WGS84SRS As New OGRSpatialReference     ' Coordinate system in WGS84

Private MapSRS As OGRSpatialReference       ' Coordinate system of map

Private ctWGS84toMap As OGRCoordinateTransformation       ' Coordinate transform from WGS84 to map

 

With WGS84SRS

    GDALError = .SetProjCS("WGS84 Datum")

    Debug.Assert(GDALError = OGRError.OGRERR_NONE, GetLastErrorMsg())

    GDALError = .SetWellKnownGeogCS("WGS84")          ' Define WGS84 coordinate system

    Debug.Assert(GDALError = OGRError.OGRERR_NONE, GetLastErrorMsg())

End With

 

With MapSRS

     GDALError = .SetProjCS("Map coordinate system")

     Debug.Assert(GDALError = OGRError.OGRERR_NONE, GetLastErrorMsg())

     GDALError = .ImportFromEPSG(3577)

     Debug.Assert(GDALError = OGRError.OGRERR_NONE, GetLastErrorMsg())

End With

 

ctWGS84toMap = GDAL.CreateCoordinateTransformation(WGS84SRS, MapSRS)        ' Create a coordinate transformation - WGS84 to map

Debug.Assert(ctWGS84toMap IsNot Nothing, GetLastErrorMsg())

 

Marc,

Can you provide the code leading to the error?

On Tue, Oct 18, 2011 at 1:21 PM, Marc Hillman <dev4cx4m9z at snkmail.com> wrote:

I have a GIS database, and all data is stored in WGS84 datum. I have developed an application using GDAL, and I now need to translate my WGS84 coordinates to several different datums, depending what map is loaded. I seem to be going around in circles, and need a nudge in the right direction. I am defining an OGRSpatialReference for each datum (WGS84 and current map) and then attempting to create an OGRCoordinateTransformation for the transformation.. This last step fails with a PROJ.4 error (“No PROJ.4 translation for destination SRS, coordinate transformation initialization failed”

 

My question is - Do I need PROJ.4 to do the translation? Can I not just use ImportFromWKT to define my OGRSpatialReference? If so, is there a nice canned list of all the WKT somewhere?  I’m keen to avoid PROJ.4 if possible as I’m not sure I can build it.

 


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