WrapDateline hack, for tile maps

[Charlie Tennessen]

I have written a halfway decent hack to get OpenScales to draw a map across the dateline.  You will need to ask for the maps as though the Eastern Hemisphere goes beyond 180 degrees, eg, 200 degrees = -160 Lon.  This is how dateline wrapping works in OpenGIS, which is the last map server that I wrote a map client for.  So, here is a simple hack:

//here is an example of calling a map across the dateline

_map.zoomToExtent(new Bounds( 160, -10, 240, 70));

Make the following changes to location.as, grid.as, tile.as, and tms.as:

location.as

//add setter so lon can be changed from grid.as for dateline wrapping

public function set lon(value:Number):void 

{

_x = value;

}

grid.as

//add this right before "stretchedWidth" is set in the loop

if (upRigth.lon < bottomLeft.lon) {

upRigth.lon += 360;

}

tile.as

//we are going to be overriding function withinMapBounds() so we need to hack it a bit

private var _withinBounds:Boolean = false; //add this var

public function withinMapBounds():Boolean //rewrite existing function to look like this

{

if (_withinBounds) {

return true;

}else {

if(this.layer == null || !(this.layer is Grid))

return false;

if(!this.layer.maxExtent || !this.bounds.intersectsBounds(this.layer.maxExtent, false))

return false;

if(!this.bounds.intersectsBounds(this.layer.map.maxExtent, false))

return false;

if((this.layer as Grid).buffer == 0

//&& !this.bounds.intersectsBounds(this.layer.map.getExtentForResolution((this.layer as Grid).requestedResolution), false))

&& !this.bounds.intersectsBounds(this.layer.map.extent, false))

return false;

return true;

}

}

//add getters and setters

/**

 * Manual override for wrapping dateline

 */

public function get withinBounds():Boolean 

{

return _withinBounds;

}

/**

 * Manual override for wrapping dateline

 */

public function set withinBounds(value:Boolean):void 

{

_withinBounds = value;

}

}

tms.as

//here is where the main hack is

override public function addTile(bounds:Bounds, position:Pixel):ImageTile { //rewrite existing function to look like this

var newBounds:Bounds = bounds.clone();

//re-working the bounds so that getURL returns a good url for the tiles we will be wrapping

if (maxExtent != null)

{

//shift right? 

while (newBounds.left < maxExtent.left && newBounds.right <= maxExtent.left)

{

newBounds = newBounds.add(maxExtent.width, 0);

}

//shift left? 

while (newBounds.left >= maxExtent.right && newBounds.right > maxExtent.right)

{

newBounds = newBounds.add( -maxExtent.width, 0);

}

}

var tl:ImageTile = new ImageTile(this, position, newBounds, this.getURL(newBounds), new Size(this.tileWidth, this.tileHeight));

if (!tl.withinMapBounds()) { //you can also just set every tl.withinBounds = true, but I'm trying to be efficient

var tmpB:Bounds = tl.bounds.clone();

tmpB = tmpB.reprojectTo("EPSG:4326"); //4326 is the only projection i understand!

if (tmpB.left + 360 < maxExtent.right) {

tl.withinBounds = true;

}

}

return tl;

}

I will not be dragging or wheeling in my application so I did not go very far on this.  You can drag and zoom a bit with this modification, but it crashes ("Error #2015: Invalid BitmapData.
") if you don't throttle the zoom and pan updates.  I would REALLY love it if someone wrote a genuine update so openscales would naturally pan across 180/-180!  This looks like a mostly dead forum but maybe someone will get this message in a bottle and move forward on this issue.  BTW I am using Bing maps.  Good luck and happy coding.