Re: [Geotools-gt2-users] New Zealand Map Grid projection?

[Rueben S. <r_j...@ya...>]

Hello,

Geotools does not (yet) support the new zealand map grid projection. If
we did support it, your WKT below looks correct. For some information on
this projection, see the epsg guide book 7-2 (page 47 in the pdf) at:
 
http://www.ihsenergy.com/epsg/guid7_2.html

>From the epsg info, it looks like an oblique mercator projection would
be closer than a transverse mercator, but neither will give you the
correct calculations!!!

For a list of projections implemented in geotools, see:

http://docs.codehaus.org/display/GEOTOOLS/Coordinate+Transformation
+Parameters

For the 2.1.x development branch, the oblique mercator projection and
NADCON transform can now be added to this list.

Proj4 (and libproj4) implement the new zealand map grid (PJ_nzmg.c). You
could use that to project your data to something geotools can use. If
you have time, you could port the proj4 code to geotools. I will not
have any time to start new development for the next few months, but
could make time to answer any question you might have. The document:

http://docs.codehaus.org/display/GEOTOOLS/How+to+add+new+projections

is out of date, but the most of the concepts are the same with the new
org.opengis.referencing interfaces in geotools 2.1.x. The only major
difference is the handling of parameters, which I could write for you in
about an hour. Typically, it takes me about 3-4 weeks of spare time to
implement a new projection since I need to research, implement, document
and test it.

Another approach to getting this projection in geotools is to wrap the
libproj4 library. I would eventually like to do this, but my knowledge
of JNI is very limited (I was able to call libproj4 functions from java
in a quick experiment last summer).

Rueben


On Thu, 2005-27-01 at 11:17 +1100, Ben Kelley wrote:
> Hi.
> 
> I am trying to work out how to create a CoordinateSystem object for
> the New Zealand Map Grid (NZMG).
> 
> A bit of searching on the web returned the WKT for the projection,
> which looks like:
> 
> PROJECTION["New_Zealand_Map_Grid"],PARAMETER["latitude_of_origin",-41],PARAMETER["central_meridian",173],PARAMETER["false_easting",2510000],PARAMETER["false_northing",6023150],UNIT["metre",1]
> 
> If I try to do any transformations with this (i.e. after wrapping it
> into a suitable PROJCS[] definition) I get a
> CannotCreateTransformException.
> 
> As my transformations work fine for other projections, it seem that
> GeoTools 2 does not support "New_Zealand_Map_Grid".
> 
> Can anyone help out here? As far as I can tell the New Zealand grid is
> only roughly similar to a Transverse Mercator projection. Is this
> going to be the closest I can get?
> 
>  - Ben Kelley.
>