[OpenLayers-Dev] Beginner: mapping different coordinate sources systems together

naskew nick at askew.nl
Wed Apr 8 05:07:03 EDT 2009


I am fairly new to OpenLayers but not GIS or ASP.Net and I'm trying to get OpenLayers working on an ASP.Net site. I've started by copying the sample OSM + Gooogle Maps + KML Reprojection and it seems that the Open Street Maps and Google layers are working fine. However the KML is not being projected onto the same coordinate system as the tiles (the KML is is WGS84/EPSG:4326) and all the points appear to be being rendered somewhere just off the west coast of Africa (where I guess 0,0 is for the tile coordinate system EPSG:900913) but clearly at different points if you zoom in enough.

It all seems to work on the openlayers sample site and I'm sure that I've copied the code correctly (I've pasted it below, I removed the google stuff just to make this as simple as possible). Is there perhaps something tricky to setting up the reprojection?

I've worked with a local copy of OpenLayers.js and the separate file version and the hosted version, they all give the same result. 

var map, select;

function init(){

    window.onresize = onWindowResize;
    var options = {
        projection: new OpenLayers.Projection("EPSG:900913"),
        displayProjection: new OpenLayers.Projection("EPSG:4326"),
        units: "m",
        maxResolution: 156543.0339,
        maxExtent: new OpenLayers.Bounds(-20037508.34, -20037508.34,
                                         20037508.34, 20037508.34)
    map = new OpenLayers.Map('map', options);
    var mapnik = new OpenLayers.Layer.TMS(
        "OpenStreetMap (Mapnik)",
            type: 'png', getURL: osm_getTileURL,
            displayOutsideMaxExtent: true,
            attribution: ' OpenStreetMap '

    var sundials = new OpenLayers.Layer.Vector("KML", {
        projection: map.displayProjection,
        strategies: [new OpenLayers.Strategy.Fixed()],
        protocol: new OpenLayers.Protocol.HTTP({
            url: "kml/sundials.kml",
            format: new OpenLayers.Format.KML({
                extractStyles: true,
                extractAttributes: true
    map.addLayers([mapnik, sundials]);

    select = new OpenLayers.Control.SelectFeature(sundials);
        "featureselected": onFeatureSelect,
        "featureunselected": onFeatureUnselect


    map.addControl(new OpenLayers.Control.LayerSwitcher());

        new OpenLayers.Bounds(
            16, 33, 47, 54
        ).transform(map.displayProjection, map.projection)

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