[OpenLayers-Users] Static images, bounds and zoom

[XinGang Li]

You can use below patch:

Index: lib/OpenLayers/Layer/Image.js
===================================================================
--- lib/OpenLayers/Layer/Image.js    (revision 8489)
+++ lib/OpenLayers/Layer/Image.js    (working copy)
@@ -47,13 +47,6 @@
     tile: null,

     /**
-     * Property: aspectRatio
-     * {Float} The ratio of height/width represented by a single pixel in
the
-     * graphic
-     */
-    aspectRatio: null,
-
-    /**
      * Constructor: OpenLayers.Layer.Image
      * Create a new image layer
      *
@@ -69,9 +62,6 @@
         this.extent = extent;
         this.size = size;
         OpenLayers.Layer.prototype.initialize.apply(this, [name, options]);
-
-        this.aspectRatio = (this.extent.getHeight() / this.size.h) /
-                           (this.extent.getWidth() / this.size.w);
     },

     /**
@@ -128,9 +118,9 @@
          * image will be stretched in one dimension only.
          */
         if( this.options.maxResolution == null ) {
-            this.options.maxResolution = this.aspectRatio *
-                                         this.extent.getWidth() /
-                                         this.size.w;
+            var wRes = this.extent.getWidth() / this.size.w;
+            var hRes = this.extent.getHeight() / this.size.h;
+            this.options.maxResolution = Math.min(wRes, hRes);
         }
         OpenLayers.Layer.prototype.setMap.apply(this, arguments);
     },
@@ -155,8 +145,10 @@
             this.setTileSize();

             //determine new position (upper left corner of new bounds)
-            var ul = new OpenLayers.LonLat(this.extent.left,
this.extent.top);
-            var ulPx = this.map.getLayerPxFromLonLat(ul);
+            var center = this.extent.getCenterLonLat();
+            var centerPx = this.map.getLayerPxFromLonLat(center);
+            var ulPx = new OpenLayers.Pixel(centerPx.x - (this.tileSize.w /
2),
+                     centerPx.y - (this.tileSize.h / 2));

             if(firstRendering) {
                 //create the new tile
@@ -175,10 +167,23 @@
      * Set the tile size based on the map size.
      */
     setTileSize: function() {
-        var tileWidth = this.extent.getWidth() / this.map.getResolution();
-        var tileHeight = this.extent.getHeight() /
this.map.getResolution();
-        this.tileSize = new OpenLayers.Size(tileWidth, tileHeight);
+        var w = this.extent.getWidth() / this.map.getResolution();
+        var h = this.extent.getHeight() / this.map.getResolution();
+
+        this.tileSize = this.getLockedSize(w, h);
     },
+
+    getLockedSize: function(w, h) {
+        var tileWidth = w;
+        var tileHeight = h;
+        if(this.size.h > this.size.w) {
+            tileHeight = Math.floor(this.size.h * (w / this.size.w));
+        } else {
+            tileWidth = Math.floor(this.size.w * (h / this.size.h));
+        }
+
+        return new OpenLayers.Size(tileWidth, tileHeight);
+    },

     /**
      * APIMethod: setUrl

If this is the right way for the image layer, I will open a ticket for this
patch.


> Hi,
>
> I'm using OpenLayers to develop a viewing application for medical images.
> So far I'm just using static images, i.e. I'm using the Image layer, and I'm
> a bit puzzled as to the interdependence of bounds, extent, resolution and
> all this stuff. I simply want to fit an image which might be quite high-res
> into the viewport for a start and then let the users zoom in until the
> natural resolution of the image is reached. I played with all the parameters
> but to be honest I still haven't quite gotten the gist, so even after hours
> it seems as if I'm not a step further. A hint or short explanation as to how
> to approach this would be greatly appreciated!
>
> My code is something like this:
> var oMapWest = new OpenLayers.Map('viewportWest');
> var graphic = new OpenLayers.Layer.Image(
>  'City Lights',
>  'images/political_world_map.jpg',  // which is 8000x4000pxs
>  new OpenLayers.Bounds(-180, -90, 180, 90),
>  new OpenLayers.Size(700, 350),
>  {numZoomLevels:10}
> );
> oMapWest.addLayers([graphic]);
> oMapWest.zoomToMaxExtent();
>
> Thanks!
>
> Flo
>
>


-- 
Li XinGang
EMail: slinavlee at gmail.com
Blog:   avlee.cnblogs.com
Site:    www.mapboost.org.cn
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