Cache proj4 transforms for transformCoordinates

src/transform.js

@@ -157,6 +157,13 @@ var transform = function (options) {
   return this;
 };
 
+/**
+ * This object stores a cache of transform classes so they don't have
+ * to be recreated on every call to transformCoordinates.
+ * @private
+ */
+var cache = {};
+
 /**
  * Transform an array of coordinates from one projection into another.  The
  * transformation may occur in place (modifying the input coordinate array),
@@ -182,7 +189,14 @@ transform.transformCoordinates = function (
   }
 
   var i, count, offset, xAcc, yAcc, zAcc, writer, output, projPoint,
-      trans = transform({source: srcPrj, target: tgtPrj});
+      trans;
+
+  if (!cache.hasOwnProperty(srcPrj) || !cache[srcPrj].hasOwnProperty(tgtPrj)) {
+    cache[srcPrj] = cache[srcPrj] || {};
+    cache[srcPrj][tgtPrj] = transform({source: srcPrj, target: tgtPrj});
+  }
+
+  trans = cache[srcPrj][tgtPrj];
 
   /// Default Z accessor
   zAcc = function () {