[OpenLayers-Users] projections, ESPG 4326 and 900913

[Andrew Schuh]

I want to say first of all that this is a great suite of code and I apologize
in advance if this question has been posed in various fashions before,
because I assume most people have run into this.  I tend to find a lot of
GIS data coming over the web in either ESPG 4326 or 900913 and often it
doesn't seem like there is a an easy way to get both on the same map.  For
example, I would like to use the USGS aerial imagery at www.terraservice.net
and overlay either political boundaries or roads or something.  Previously I
have used landsat7 w/ Mapnik using an example I found on the web.  Currently
I'm trying to bring together the terraservice w/ openstreetmap or mapnik.  I
can get terraservice working in 4326 and openstreetmap in 900913 but I can't
seem to get them together, regardless of being willing to work in either
projection.  I understand projections reasonably enough but I must be
confused about the way reprojections are available.  The type of thing I'm
trying to do is in code below (not complete).  Server side projections seem
like the way to go if they are available but I have not had much luck in
trying to reproject in this way.  Often it seems that either 4326 or 900913
is available but not the other.  I'm assuming that "projection:" arg is fed
to the WMS server to get data is that projection.  The reprojection examples
always concern a couple of points (and not layer) so I've assumed either
this can't be done w/ layers or is too inefficient.  Am I just confused
about how to do it or is there really a void between putting many maps
together on the fly?

function initmap(){
  var options = {
      //projection: "EPSG:900913",
      projection: "EPSG:4326",
      //displayProjection: new OpenLayers.Projection("EPSG:4326"),
      maxExtent: new OpenLayers.Bounds(-20037508.34, -20037508.34,
                                     20037508.34, 20037508.34),
      //maxExtent: new OpenLayers.Bounds(-130, 20,
      //                                -90, 50),
  };

  var terraservice = new OpenLayers.Layer.WMS(
      "Terraservice",
      ["http://terraservice.net/ogcmap.ashx?"],
      {'layers': 'DOQ',
      }
  );

 var mapnik = new OpenLayers.Layer.TMS(
      "Mapnik",
     
["http://t1-overlay.hypercube.telascience.org/tiles/1.0.0/osm-merc-google-hybrid/",
     
"http://t3-overlay.hypercube.telascience.org/tiles/1.0.0/osm-merc-google-hybrid/",
     
"http://t2-overlay.hypercube.telascience.org/tiles/1.0.0/osm-merc-google-hybrid/"],
      {
          type: 'png', getURL: osm_getTileURL,
          displayOutsideMaxExtent: true,
          isBaseLayer: false, visibility: true 
      }
  );

map.addLayers([terraservice,mapnik]);



I also tried to modify the javascript in the OpenStreetMap.js available for
the Open Street data by changing the parameters in the top class from 900913
to 4326 but that didn't seem to work either.   Not sure if this is even
reasonable to try.  A bit confused about this all, any help would be
appreciated.  By the way, I have used the openlayers code successfully but
just where the map servers are all providing stuff in the same projection.



/**
 * @requires OpenLayers/Layer/TMS.js
 *
 * Class: OpenLayers.Layer.OSM
 *
 * Inherits from:
 *  - <OpenLayers.Layer.TMS>
 */
OpenLayers.Layer.OSM = OpenLayers.Class(OpenLayers.Layer.TMS, {
    /**
     * Constructor: OpenLayers.Layer.OSM
     *
     * Parameters:
     * name - {String}
     * url - {String}
     * options - {Object} Hashtable of extra options to tag onto the layer
     */
    initialize: function(name, url, options) {
        options = OpenLayers.Util.extend({
            attribution: "Data by  http://openstreetmap.org/ OpenStreetMap
",
            maxExtent: new
OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34),
            maxResolution: 156543.0339,
            //maxExtent: new OpenLayers.Bounds(-130, 20,-90, 50),
            units: "m",
            //projection: "EPSG:4326",
            projection: "EPSG:900913",
            transitionEffect: "resize"
        }, options);
        var newArguments = [name, url, options];
        OpenLayers.Layer.TMS.prototype.initialize.apply(this, newArguments);
    },
-- 
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