[Gdal-dev] Re: Nad Grid with ogr2ogr

[Jeremy Palmer]

Hi Brendan,
 
First make sure you have the NZGD49 <=> NZGD2000 datum distortion grid
installed into your proj4 lib directory. 
 
You can download the grid from the:
  LINZ website
http://www.linz.govt.nz/core/surveysystem/geodeticinfo/geodeticdatums/nzgd49tonzgd2000/index.html
or
  PROJ.4 ftp ftp://ftp.remotesensing.org/proj/proj-datumgrid-1.3.zip
 
The PROJ.4 lib directory is either ms4w\proj\nad for MS4W, proj_lib for
FWTools, or can be manually set using the PROJ_LIB environment
variable.
 
I would change your command a little so you don't need to specify the
NZTM proj def on the command line. Instead I would obtain it from the
'epsg' coordinate definition file in the proj lib directory :)
 
ogr2ogr -f "ESRI Shapefile" output.shp input.shp -s_srs "+proj=nzmg
+lat_0=-41 +lon_0=173 +x_0=2510000 +y_0=6023150 +ellps=intl
+datum=nzgd49 +units=m +nadgrids=nzgd2kgrid0005.1gsb +wktext" -t_srs
EPSG:2193
 
Note the use of the "+wktext" parameter for the NZMG proj text. You
need at least OGR 1.4.0 for this to work. See
http://lists.maptools.org/pipermail/gdal-dev/2007-April/012561.html for
more info.
 
Cheers
Jeremy

>>> <bcervin at gmail.com> 20/04/2007 11:49 >>>

Hello Jeremy,

I stumbled across your discussion about nad grid and ogr2ogr. I'm
trying to do the same reprojection as you.

As I noticed that this was very recent I'm hoping you might be able to
give me some help.

I'm having difficulty with ogr2ogr, NZMG->NZTM conversion for shape
files.

I've got what i think should work but it simply isn't. This is my
command:
ogr2ogr output.shp input.shp  -t_srs '+proj=tmerc +lat_0=0.0000000000
+lon_0=173.0000000000 +k_0=0.9996000000 +x_0=1600000.0000000000
+y_0=10000000.0000000000 +a=6378137 +rf=298.257222101 +no_defs
+towgs84=0.000,0.000,0.000' -s_srs '+proj=nzmg +lat_0=-41.0000000000
+lon_0=173.0000000000 +x_0=2510000.0000000000 +y_0=6023150.0000000000
+a=6378388 +rf=297 +no_defs +nadgrids=nzgd2kgrid0005.gsb'

I suspect that your command would work perfectly for me. I'm using a
MS4W version of ogr2ogr.

Thanks for your time.

Cheers, Brendan.


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