Openlayers projection with OSM style maps and a GeoJSON vector layer

Question

Note: I know there's another question similar to this but it hasn't been answered and I need to know how mixed projections can be dealt with with GeoJSON and OSM.

I'm so confused. I was using the OSMDroid API on Android for mapping and wanted to replicate it using OpenLayers and GeoExt, but I've got a projection problem with including GeoJSON nodes and action events.

My tile set is OSM based, and is hosted on the same Web server as this HTML/JS. See it all below. I realize my boundaries aren't working, and my projections might be completely wrong. I've been testing different combinations.

The problem is my map displays correctly and is centered fine. However:

1. My GeoJSON feature nodes are way off the map. They're in a different projection long/lat, but I don't know how to set or convert GeoJSON long/lat to the current map projection.

2. My mapCtrl doesn't work. When I click it the lonlat is another projection (the OSM projection coords) and I can't seem to convert them)

3. Any tips on how extent/bounds actually work would be greatly appreciated

Can someone please help with a bit of projection advice? Sigh... I'm not patient enough for this.

Here's my full JS, as is:

var mapPanel, store, gridPanel, mainPanel, nodePop, mapPop;

Ext.onReady(function() {

    var map, mapLayer, vecLayer;
    var lon = -70.885610;
    var lat = 38.345822;
    var zoom = 17;
    var maxZoom = 18;

var toProjection = new OpenLayers.Projection("EPSG:4326");
var fromProjection = new OpenLayers.Projection("EPSG:900913");
    var extent = new OpenLayers.Bounds(-1.32,51.71,-1.18,51.80).transform(fromProjection, toProjection);

    // Setup the node layer feature store and push it all into a vector layer
    vecLayer = new OpenLayers.Layer.Vector("vector");
    store = new GeoExt.data.FeatureStore({
        layer: vecLayer,
        fields: [
            {name: 'name', type: 'string'},
            {name: 'status', type: 'string'}
        ],
        proxy: new GeoExt.data.ProtocolProxy({
            protocol: new OpenLayers.Protocol.HTTP({
                url: "data/sa.json",
                format: new OpenLayers.Format.GeoJSON()
            })
        }),
        autoLoad: true
    });

    // Setup the basic map layer using OSM style tile retreival to pull tiles
    // from the same server hosting this service
    map = new OpenLayers.Map(
        'map', {
            controls:[
                new OpenLayers.Control.Navigation(),
                new OpenLayers.Control.PanZoomBar(),
                new OpenLayers.Control.Attribution(),
                new OpenLayers.Control.ScaleLine()],
            projection: toProjection,
            displayProjection: fromProjection,
            numZoomLevels: 20,
            fractionalZoom: true
        });

    mapLayer = new OpenLayers.Layer.OSM(
        "Local Tiles",
        "tiles/${z}/${x}/${y}.png",
        {
            zoomOffset: 17,
            resolutions: [1.194328566741945,0.5971642833709725,0.2985821416854863] // Zoom level 17 - 19
        });

    map.addLayers([mapLayer, vecLayer]);

    // Create a map panel
    mapPanel = new GeoExt.MapPanel({
            title: "Map",
            region: "center",
            map: map,
            xtype: "gx_mappanel",
            center: new OpenLayers.LonLat(lon, lat),
            zoom: zoom
    });

    // Create a grid panel for listing nodes
    gridPanel = new Ext.grid.GridPanel({
            title: "Nodes",
            region: "east",
            store: store,
            width: 275,
            columns: [{
                header: "Name",
                width: 200,
                dataIndex: "name"
            }, {
                header: "Status",
                width: 75,
                dataIndex: "status"
            }],
            sm: new GeoExt.grid.FeatureSelectionModel({
                autoPanMapOnSelection: true
                })
    });

    // Create the main view port
    new Ext.Viewport({
        layout: "border",
        items: [{
            region: "north",
            contentEl: "title",
            height: 150
        }, mapPanel, gridPanel]
    });
    var lonLat = new OpenLayers.LonLat(lon, lat).transform(new OpenLayers.Projection("EPSG:4326"), map.getProjectionObject());
    map.setCenter(lonLat, zoom);


    // Attach all the event driven stuff here...
    // Create a node selection pop up control
    function nodeAction(feature) {
        nodePop = new GeoExt.Popup({
            title: 'Node selected',
            location: feature,
            width: 200,
            html: "",
            maximizable: true,
            collapsible: true
        });
        nodePop.on({
            close: function() {
                if(OpenLayers.Util.indexOf(vectorLayer.selectedFeatures, this.feature) > -1) {
                    selectCtrl.unselect(this.feature);
                }
            }
        });
        nodePop.show();
    };

    // Attach the pop to node/feature selection events
    var selectCtrl = new OpenLayers.Control.SelectFeature(vecLayer);
    vecLayer.events.on({
        featureselected: function(e) {
            nodeAction(e.feature);
        }
    });

    // Create map selection pop up control
    function mapAction(lonlat) {
        mapPop = new GeoExt.Popup({
            title: 'Map selected',
            location: lonlat,
            width: 200,
            html: "You clicked on (" + lonlat.lon.toFixed(2) + ", " + lonlat.lat.toFixed(2) + ")",
            maximizable: true,
            collapsible: true,
            map: mapPanel.map,
            anchored: true
        });
        mapPop.doLayout();
        mapPop.show();
    };

    var mapCtrl = new OpenLayers.Control.Click({
        trigger: function(evt) {
            var lonlat = mapPanel.map.getLonLatFromViewPortPx(evt.xy);
            lonlat.transform(new OpenLayers.Projection("EPSG:4326"), mapPanel.map.getProjectionObject());

            //.transform(new OpenLayers.Projection("EPSG:4326"), map.getProjectionObject());

            mapAction(lonlat);
        }
    });
    mapPanel.map.addControl(mapCtrl);
    mapCtrl.activate();
});

// A control to handle user clicks on the map
OpenLayers.Control.Click = OpenLayers.Class(
    OpenLayers.Control, {
        defaultHandlerOptions: {
            single: true,
            double: false,
            pixelTolerance: 0,
            stopSingle: true
        },
        initialize: function(options) {
            this.handlerOptions = OpenLayers.Util.extend(
                options && options.handlerOptions || {},
                this.defaultHandlerOptions
            );
            OpenLayers.Control.prototype.initialize.apply(
                this, arguments
            );
            this.handler = new OpenLayers.Handler.Click(
                this,
                { click: this.trigger },
                this.handlerOptions
            );
        },
        CLASS_NAME: "OpenLayers.Control.Click"
    }
);

Here's the GeoJSON I'm using:

{
  "type": "FeatureCollection",
  "features": [
    {
      "geometry": {
        "type": "Point",
        "coordinates": [
          -70.3856,
      38.3458
        ]
      },
      "type": "Feature",
      "properties": {
        "name": "Node0",
        "status": "Active",
        "externalGraphic": "img/node2.png",
        "graphicHeight": 75, "graphicWidth": 75
      },
      "id": 100
    },
    {
      "geometry": {
        "type": "Point",
        "coordinates": [
          -70.885810,
      38.344722
        ]
      },
      "type": "Feature",
      "properties": {
        "name": "Node1",
        "status": "Active",
        "externalGraphic": "img/node2.png",
        "graphicHeight": 75, "graphicWidth": 75
      },
      "id": 101
    }
  ]
}

Answer 1

Ok, here's how I dealt with the issue:

1. I'm using the embedded the Jetty Web server in my back-end, but regardless, I created a servlet to respond with GeoJSON format data. Each Feature location lon/lat is converted between projections. (e.g. EPSG:4326 to EPSG:900913)

2. The lon/lat projection conversation leveraged the GeoTools Java API. This blog post was particularly helpful (http://ariasprado.name/2012/08/13/quick-and-dirty-coordinate-transforming-using-geotools.html) Note that you'll need to go through a fair bit of trial and error if you only want to include the jars required for converting yout projections. GeoTools is large, does a lot, and has a number of jars.

Now when the GeoExt.data.ProtocolProxy loads my GeoJSON content it's already in OSM compatible EPSG:900913. I would have liked to deal with this entirely in GeoExt/OpenLayer, but there doesn't appear to be an easy way. I will acknowledge that GeoExt and OpenLayers don't have super great reference documentation to follow.

I'd include my GeoTools code but "Arias Prado GIS Ramblings" blog post above does a better job than I could. Again though, note that you'll have to trial and error the jars. Projection encoders are loaded dynamically, and they in turn have class dependencies from other jars.