#PROJ4JS

Proj4js is a JavaScript library to transform point coordinates from one coordinate system to another, including datum transformations. Originally a port of PROJ.4 and GCTCP C it is a part of the MetaCRS group of projects.

##Installing

Depending on your preferences

npm install proj4
bower install proj4js
jam install proj4

or just manually grab the file dist/proj4.js

##Using

the basic signature is:

proj4(fromProjection[, toProjection2, coordinates])

Projections can be proj or wkt strings, or a proj4.Proj object.

Coordinates may be proj4.Point objects, an object of the form {x:x,y:y}, or an array of the form [x,y].

When all 3 arguments are given, the result is that the coordinates are transformed from projection1 to projection 2. And returned in the same format that they were given in.

var firstProjection = 'PROJCS["NAD83 / Massachusetts Mainland",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHEROID["GRS 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4269"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["standard_parallel_1",42.68333333333333],PARAMETER["standard_parallel_2",41.71666666666667],PARAMETER["latitude_of_origin",41],PARAMETER["central_meridian",-71.5],PARAMETER["false_easting",200000],PARAMETER["false_northing",750000],AUTHORITY["EPSG","26986"],AXIS["X",EAST],AXIS["Y",NORTH]]';
var secondProjection = "+proj=gnom +lat_0=90 +lon_0=0 +x_0=6300000 +y_0=6300000 +ellps=WGS84 +datum=WGS84 +units=m +no_defs";
//I'm not going to redefine those two in latter examples.
proj4(firstProjection,secondProjection,[2,5]);
// [-2690666.2977344505, 3662659.885459918]

If only 1 projection is given then it is assumed that it is being projected from WGS84 (fromProjection is WGS84).

proj4(firstProjection,[-71,41]);
// [242075.00535055372, 750123.32090043]

If no coordinates are given an object with two methods is returned, its methods are forward which projects from the first projection to the second and inverse which projects from the second to the first.

proj4(firstProjection,secondProjection).forward([2,5]);
// [-2690666.2977344505, 3662659.885459918]
proj4(secondProjection,firstProjection).inverse([2,5]);
// [-2690666.2977344505, 3662659.885459918]

and as above if only one projection is given, it's assumed to be coming from wgs84

proj4(firstProjection).forward([-71,41]);
// [242075.00535055372, 750123.32090043]
proj4(firstProjection).inverse([242075.00535055372, 750123.32090043]);
//[-71, 40.99999999999986]
//the floating points to answer your question

##Developing to set up build tools make sure you have node installed and run npm install

to build run grunt if that doesn't work try:

npm install -g grunt-cli #you may need a sudo in front of that