proj4
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Proj4js is a JavaScript library to transform point coordinates from one coordinate system to another, including datum transformations.
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#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](http://trac.osgeo.org/proj/) and [GCTCP C](http://edcftp.cr.usgs.gov/pub//software/gctpc) it is
a part of the [MetaCRS](http://wiki.osgeo.org/wiki/MetaCRS) group of projects.
##Installing
Depending on your preferences
```bash
npm install proj4
bower install proj4
jam install proj4
component install proj4js/proj4js
```
or just manually grab the file `dist/proj4.js`
##Using
the basic signature is:
```javascript
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.
```javascript
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).
```javascript
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.
```javascript
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
```javascript
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 and grunt-cli installed and then run `npm install`
to do the complete build and browser tests run
```bash
grunt
```
to run node tests run
```bash
npm test
```
to run node tests with coverage run
```bash
node test --coverage
```
to create a build with only default projections (latlon and Mercator) run
```bash
grunt build
```
to create a build with only custom projections include a comma separated list of projections codes (the file name in 'lib/projections' without the '.js') after a colon, e.g.
```bash
grunt build:tmerc
#includes transverse Mercator
grunt build:lcc
#includes lambert conformal conic
grunt build:omerc,moll
#includes oblique Mercator and Mollweide
```