[OpenLayers-Dev] Grid.js, XYZ.js, ArcGISCache.js - Inconsistent behaviour between getURL function and placement of tiles

[Robert Sanson]

Hi developers
 
I have been struggling with trying to get tiles requested from an ArcGIS tile cache to line up correctly with other data (requested via Layer.WMS etc). I have tried both Layer.XYZ and Layer.ArcGISCache (from T Schaub's sandbox).
 
It seems Layer.XYZ and Layer.ArcGISCache are requesting the correct tiles, as calculated down from the specified layer tileOrigin or from the specified map maxExtent left and top values. However, the code that calculates where to put each tile is trying to work up from the maxExtent left and bottom values.
 
The north-south displacement of the tiles changes depending on the zoom level. I have managed to find a lower left coordinate pair that I can specify in the map's maxExtent left and bottom that coincide exactly with the tile corners for most of the zoom levels but not for all zoom levels.
 
I would like to see the positioning worked down from the layer tileOrigin, using tileSize and resolution, rather than up from the lower left of the map maxExtent bounds.
 
Is it possible to modify the OL code so that the map maxExtent  and restrictedExtent apply as map only properties, and allow one to specify the tileOrigin for each tile cache layer plus a property that indicates whether the tileOrigin is top left or bottom left? ArcGIS Server caches are all worked down from the top left.
 
In the meantime, I have tried to add a "zoomend" event listener that traps when the zoomend event has occurred on the map, and set a new maxExtent in order to try and force OL to re-work out the tile placements, but to no avail.
 
Here is my code:
 
var mapoptions = {
                maxExtent: new OpenLayers.Bounds(-4020900, 4554869.11353823, 2568710.79993, 19998100),
                restrictedExtent: new OpenLayers.Bounds(980902.6296,4672753.201,2606505.881,6298356.452),
                resolutions: new Array(3175.0063500127003, //0
                                       793.75158750317507, //1
                                       264.58386250105838, //2
                                       198.43789687579377, //3
                                       132.29193125052919, //4
                                       66.145965625264594, //5
                                       26.458386250105836, //6
                                       19.843789687579378, //7
                                       13.229193125052918, //8
                                       9.260435187537043, //9
                                       6.6145965625264589, //10
                                       5.2916772500211673, //11
                                       3.9687579375158752, //12
                                       2.6458386250105836, //13
                                       1.9843789687579376, //14
                                       1.3229193125052918),//15
                tileSize: new OpenLayers.Size(256,256),
                units: 'm',
                projection: new OpenLayers.Projection('EPSG:2193'),
                fractionalZoom: false
                };
var map = new OpenLayers.Map( 'map',mapoptions );
var topoagc = new OpenLayers.Layer.ArcGISCache({
                          name: "agscache",
                          url: "http://ws-esrimt/MapCache/mapservice_topography_vector_prod/Layers/_alllayers/",
                          tileOrigin: new OpenLayers.LonLat(-4020900,19998100)
 });
map.addLayers([topoagc]);
 
map.events.register('zoomend', null, function() {
                  var zm = map.getZoom();
                  var curcenter = new OpenLayers.LonLat(map.getCenter());
                  //alert(zm);
                  if (zm == 9) {
                    alert("scale = 1:35000");
                    map.maxExtent.bottom = 4553175.77681822;
                  }
                  else {
                    map.maxExtent.bottom = 4554869.11353823;
                  }
                  map.setCenter(curcenter);
});
 
Any help appreciated.
 
Many thanks,
 
Robert Sanson


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