add speed and zoomFactor args to zoomPanTo, update API

API.md

@@ -28,10 +28,12 @@ Options that define the initial position of the map unless `hash` is set to true
 #### Methods
 
 - **setPosition**_(zoom, lat, lon, angle)_ - set map position (zoom, center, rotation)
-- **zoomTo**_(zoom, duration)_ - zoom to a certain zoom level with easing
-- **scaleTo**_(scale, duration)_ - zoom by a certain scale with easing
-- **panTo**_(lat, lon, duration)_ - pan to a certain location level with easing
-- **panBy**_(x, y, duration)_ - pan by a certain number of pixels with easing
+- **zoomTo**_(zoom, duration?)_ - zoom to a certain zoom level with easing (duration in ms, 500 by default)
+- **scaleTo**_(scale, duration?)_ - zoom by a certain scale with easing
+- **panTo**_(lat, lon, duration?)_ - pan to a certain location level with easing
+- **zoomPanTo**_(lat, lon, zoom?, speed?, zoomFactor?)_ - zoom-pan optimal path easing to a specified location,
+optionally passing animation speed (1.2 by default) and zoomFactor (1.42 by default, bigger value means more pronounced zoom out)
+- **panBy**_(x, y, duration?)_ - pan by a certain number of pixels with easing
 - **stop**_() - stop current animation
 - **resize**_()_ - detect the map's new width and height and resize it
 - **setAngle**_(center, angle)_ - sets map rotation angle in radians (doesn't care for center)

js/ui/easings.js

@@ -98,7 +98,7 @@ util.extend(exports, {
         map.setAngle(center, 0);
     },
 
-    zoomPanTo: function(lat, lon, zoom) {
+    zoomPanTo: function(lat, lon, zoom, V, rho) {
         var tr = this.transform,
             fromX = tr.lonX(tr.lon),
             fromY = tr.latY(tr.lat),
@@ -110,11 +110,12 @@ util.extend(exports, {
             startWorldSize = tr.worldSize;
 
         zoom = zoom === undefined ? startZoom : zoom;
+        rho = rho || 1.42;
+        V = V || 1.2;
 
         var w0 = Math.max(tr.width, tr.height),
             w1 = w0 * tr.zoomScale(zoom - startZoom),
             u1 = Math.sqrt(dx * dx + dy * dy),
-            rho = 1.42,
             rho2 = rho * rho;
 
         function r(i) {
@@ -132,7 +133,7 @@ util.extend(exports, {
         function u(s) { return w0 * (cosh(r0) * tanh(r0 + rho * s) - sinh(r0)) / rho2; }
 
         var S = (r(1) - r0) / rho,
-            duration = 1000 * S * 0.8,
+            duration = 1000 * S / V,
             map = this;
 
         this.stop = util.timed(function (t) {