[OpenLayers-Dev] New Zealand Map Grid in OpenLayer and Proj4js

[Stephen Irons]

I have implemented a Proj4js transformation for New Zealand Map Grid (NZMG)
co-ordinates (EPSG:27200). spatial-reference.org gives a description of the
transformation, but the '+proj=nzmg' was not available in the current
version in the repository. This projection is not related to any of the
existing types, so I implemented it.

I would like to contribute this code to Proj4js. However, it is not obvious
how to submit this code to the project. Can anyone here point me to the
right place?

Stephen Irons


Background

New Zealand Map Grid (NZMG) is a projection used to convert latitude and
longitude to easting and northing coordinates in metres. It was designed to
minimize the scale error over the land area of New Zealand and cannot be
used elsewhere.

The New Zealand govnernment survey agency, LINZ (Land Information New
Zealand) has published two series of maps covering the mainland areas of New
Zealand.

   - 262-series is 1:250000
   - 260-series is 1:50000

These maps are available in printed form and are currently the only
large-scale maps of New Zealand widely available to the general public.
Vector data is also available.

Various commercial concerns have scanned these maps, or generated tiles from
the vector data, and released products using these tiles. I have one of
these products and want to use the tiles with OpenLayers.

New Zealand Map Grid

New Zealand Map Grid was designed by Dr W. I. Reilly in 1973. Its official
specification is published as *New Zealand Map Grid*, Department of Lands
and Survey Technical Circular 1973/32. A scanned image of the publication is
available at
http://www.linz.govt.nz/docs/miscellaneous/nz-map-definition.pdf

It is also described in *Conversion between Latitude and Longitude and New
Zealand Map Grid*, OSG Technical Report 4.1, 1998. This document is
available at http://www.linz.govt.nz/docs/miscellaneous/nzmg.pdf

NZMG is given EPSG code EPSG:27200. It is defined at
http://spatialreference.org/ref/epsg/27200/proj4/ as

   - "+proj=nzmg +lat_0=-41 +lon_0=173 +x_0=2510000 +y_0=6023150 +ellps=intl
   +datum=nzgd49 +units=m +no_defs"

Now, most of this is known to Proj4js code. However, the projections 'nzmg'
is not know, and needs to be implemented.
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