Retrieve list of all features and values from raster layer (GeoServer and OpenLayers2)

Question

I'm trying to retrieve a list of all values from a raster layer (GeoTIFF) in GeoServer (2.5.x).

I tried to modify the code from http://trac.osgeo.org/openlayers/wiki/GetFeatureInfo but I can't seem to find a way to do this. I create a custom control that uses the OpenLayers.Handler.Box as input. This gives me back the right bounds (selected rectangle coordinates) but how do I send the bounds to GeoServer WMS?

I can code a Python module to send the bounds to and extract the values from the raster and send it back to my web application but I thought this must be possible from within OpenLayers?

Does anyone have an example of how do extract a range of values from a raster using GeoServer and OpenLayers?

My code so far:

function findLayerClick(event) {
    mouseLoc = map.getLonLatFromPixel(event.xy);
    layerlist = 'mylayer';
    //GetCoverage
    var url = sec.getFullRequestString({
                                        REQUEST: "GetFeatureInfo",
                                        EXCEPTIONS: "application/vnd.ogc.se_xml",
                                        BBOX: map.getExtent().toBBOX(),
                                        X: event.xy.x,
                                        Y: event.xy.y,
                                        INFO_FORMAT: 'text/plain',
                                        QUERY_LAYERS: layerlist,
                                        FEATURE_COUNT: 50,
                                        WIDTH: map.size.w,
                                        HEIGHT: map.size.h},
                                        "http://localhost:8080/geoserver/wms");

    var request = OpenLayers.Request.GET({
      url: url,
      callback: extractFeatures
    });
  }

  function extractFeatures(e) {
    console.log(e);
  }

My map, layers, and the control handling the box select:

function init() {
    wgs84 = new OpenLayers.Projection('EPSG:4326');
    googleProjection = new OpenLayers.Projection('EPSG:900913');

var options = {
      controls: [
                  new OpenLayers.Control.LayerSwitcher(),
                  new OpenLayers.Control.Navigation({zoomWheelEnabled: true, handleRightClicks: true}),
                  new OpenLayers.Control.PanZoom(),
                  new OpenLayers.Control.DragPan(),
                  new OpenLayers.Control.ScaleLine({maxWidth:200})
                ],

      div: 'map-canvas',
      theme: null,
      units: 'm',
      projection: googleProjection,
      displayProjection: wgs84,
      maxResolution: 'auto',

      eventListeners: {
          'movestart': function(e) {
          },
          'zoomend': function(e) {
              zoomBoxControl.deactivate();
          }
      }
    };

    map = new OpenLayers.Map(options);

    var ghyb = new OpenLayers.Layer.Google(
        "Google Physical",
        {
          type: google.maps.MapTypeId.TERRAIN,
          minZoomLevel: 1,
          numZoomLevels: 11,
          sphericalMercator: true,
          projection: 'EPSG:900913'
        }
    );

    //this is the raster layer
    sec = new OpenLayers.Layer.WMS(
      "mylayer",
      "http://localhost:8080/geoserver/wms",
      {layers: 'mylayer', format:'image/png', transparent:'true'},
      {opacity: 1.0, visibility: true, displayInLayerSwitcher: true, isBaseLayer: false}
    );

     OpenLayers.Util.extend(control, {
      draw: function () {
          this.drag = new OpenLayers.Handler.Box( control,
              {"done": this.notice},
              {keyMask: OpenLayers.Handler.MOD_CTRL});
          this.drag.activate();
      },

      notice: function (bounds) {
        mybounds = bounds;


        console.log(mybounds);

        var lowerLeft = map.getLonLatFromPixel(new OpenLayers.Pixel(mybounds.left, mybounds.bottom));
        var upperRight = map.getLonLatFromPixel(new OpenLayers.Pixel(mybounds.right, mybounds.top));

        mybounds = new OpenLayers.Bounds();
        mybounds.extend(lowerLeft);
        mybounds.extend(upperRight);

        //findLayerClick(mybounds);
        return(true);
      }
    });
  }

The findLayerClick function returns back a valid value of a clicked pixel but i need the list (table, array or whatever) of values in the selected range. Hope someone can help me.

Answer 1

I tried to modify the code from http://trac.osgeo.org/openlayers/wiki/GetFeatureInfo but I can't seem to find a way to do this.

You can't use a WMS GetFeatureInfo request to retrieve a range of values, because it only works on a point location (in a GetMap image.) This is a limitation of the WMS specification.

Furthermore a WMS doesn't give you the actual values from your input data (even if it's a raster dataset) it gives a representation of the data. If you want to get at the data values in a GeoTIFF sitting on GeoServer you will need to configure a WCS service.