Expose methods to define new proj4 definitions

src/transform.js

@@ -1,3 +1,5 @@
+var proj4 = require('proj4');
+
 //////////////////////////////////////////////////////////////////////////////
 /**
  * This purpose of this class is to provide a generic interface for computing
@@ -28,8 +30,6 @@ var transform = function (options) {
     return new transform(options);
   }
 
-  var proj4 = require('proj4');
-
   var m_this = this,
       m_proj,   // The raw proj4js object
       m_source, // The source projection
@@ -157,6 +157,52 @@ var transform = function (options) {
   return this;
 };
 
+/**
+ * Contains a reference to `proj4.defs`.  The functions serves two
+ * purposes.
+ *
+ *   1. It is a key value mapping of all loaded projection definitions
+ *   2. It is a function that will add additional definitions.
+ *
+ * See:
+ *   http://proj4js.org/
+ */
+transform.defs = proj4.defs;
+
+/**
+ * Look up a projection definition from epsg.io
+ * For the moment, we only handle `EPSG` codes.
+ *
+ * @param {string} projection A projection alias (e.g. EPSG:4326)
+ * @returns {promise} Resolves with the proj4 definition
+ */
+transform.lookup = function (projection) {
+  var $ = require('jquery');
+  var code, defer = new $.Deferred(), parts;
+
+  if (proj4.defs.hasOwnProperty(projection)) {
+    return defer.resolve(proj4.defs[projection]);
+  }
+
+  parts = projection.split(':');
+  if (parts.length !== 2 || parts[0].toUpperCase() !== 'EPSG') {
+    return defer.reject('Invalid projection code').promise();
+  }
+  code = parts[1];
+
+  return $.ajax({
+    url: 'http://epsg.io/?q=' + code + '&format=json'
+  }).then(function (data) {
+    var result = (data.results || [])[0];
+    if (!result || !result.proj4) {
+      return defer.reject(data).promise();
+    }
+
+    proj4.defs(projection, result.proj4);
+    return $.when(proj4.defs[projection]);
+  });
+};
+
 /**
  * Transform an array of coordinates from one projection into another.  The
  * transformation may occur in place (modifying the input coordinate array),

tests/cases/transform.js

@@ -92,4 +92,87 @@ describe('geo.transform', function () {
       [{x: 1669792, y: -19971868}, {x: 1669792, y: -19971868}]
     ]
   );
+
+  describe('defs', function () {
+    var server;
+
+    beforeEach(function () {
+      server = sinon.fakeServer.create();
+    });
+
+    afterEach(function () {
+      server.restore();
+    });
+
+    it('predefined definitions', function () {
+      expect(geo.transform.defs.hasOwnProperty('EPSG:4326')).toBe(true);
+      expect(geo.transform.defs.hasOwnProperty('EPSG:3857')).toBe(true);
+    });
+
+    it('custom definition', function () {
+      geo.transform.defs('my projection', '+proj=longlat +datum=WGS84 +no_defs');
+      expect(geo.transform.defs.hasOwnProperty('my projection')).toBe(true);
+      var p = geo.transform({source: 'EPSG:4326', target: 'my projection'});
+
+      expect(p.forward({x: 10, y: -10, z: 0})).toEqual({x: 10, y: -10, z: 0});
+    });
+
+    it('lookup', function () {
+      var spy = sinon.spy(), request;
+      geo.transform.lookup('EPSG:5000').then(spy);
+
+      request = server.requests[0];
+      expect(request.url).toMatch(/\?q=5000/);
+      request.respond(200, {'Content-Type': 'application/json'}, JSON.stringify({
+        status: 'ok',
+        number_result: 1,
+        results: [{
+          code: '5000',
+          kind: 'CRS-PROJCRS',
+          bbox: [
+            85.06,
+            180.0,
+            85.06,
+            180.0
+          ],
+          unit: 'degree',
+          proj4: '+proj=longlat +datum=WGS84 +no_defs',
+          name: 'WGS 84',
+          area: 'World',
+          default_trans: 0,
+          trans: [],
+          accuracy: ''
+        }]
+      }));
+
+      expect(spy.calledOnce).toBe(true);
+      expect(geo.transform.defs.hasOwnProperty('EPSG:5000')).toBe(true);
+
+      geo.transform.lookup('EPSG:5000');
+      expect(server.requests.length).toBe(1);
+    });
+
+    it('invalid projection code', function () {
+      var spy = sinon.spy(), request;
+      geo.transform.lookup('EPSG:5001').fail(spy);
+
+      request = server.requests[0];
+      request.respond(200, {'Content-Type': 'application/json'}, JSON.stringify({
+        status: 'ok',
+        number_result: 0,
+        results: []
+      }));
+
+      expect(spy.calledOnce).toBe(true);
+      expect(geo.transform.defs.hasOwnProperty('EPSG:5001')).toBe(false);
+    });
+
+    it('unknown projection type', function () {
+      var spy = sinon.spy();
+      geo.transform.lookup('unknown:5002').fail(spy);
+
+      expect(spy.calledOnce).toBe(true);
+      expect(geo.transform.defs.hasOwnProperty('unknown:5002')).toBe(false);
+    });
+  });
 });