CODEWITHSUNDEEP
openlayers
Scott B.
Scott B.

Reputation: 3

OpenLayers - Get Lat/Lon on point move

I am very new to OpenLayers, been using Google Maps for awhile but want to switch to something more open. From examples I have seen online and responses to other questions I've seen on here I've come up with this basic map with a point: http://pastie.org/3625219

I would like to get the latitude/longitude of the point after I move it. The issue I am having is converting the projection back to 4326 from 900913. Everything I've tried for a transform comes back as blank...

SO! I am sure I am missing something basic... Javascript isn't my native language. Any pointers would be appreciated.

Upvotes: 0

Views: 5988

Answers (2)

tony gil
tony gil

Reputation: 9554

@scottB examine this code that shows how to identify the correct transformations for each layer. a projection that works on openlayers might not automatically work with openstreetmaps (which is a mercator spherical projection).

i adapted this example from openlayers so that i could accomplish 2 things:

  1. save latitude and longitude of marker position

  2. place a marker by clicking on the openlayers map

    <!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" debug="true">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <title>MousePosition Control</title>
    <link rel="stylesheet" href="http://openlayers.org/dev/theme/default/style.css" type="text/css">
    <link rel="stylesheet" href="http://openlayers.org/dev/examples/style.css" type="text/css">
    <script src="../OpenLayers.js"></script>
    <script type="text/javascript">
        var map;
        function init(){
            var map = new OpenLayers.Map('map');
            var proj4326 = new OpenLayers.Projection("EPSG:4326");
            var projmerc = new OpenLayers.Projection("EPSG:900913");
            var layerOSM = new OpenLayers.Layer.OSM("Street Map");
            map.addLayers([layerOSM]);
            if (!map.getCenter()) map.zoomToMaxExtent();
            map.events.register("mousemove", map, function(e) { 
                var position = this.events.getMousePosition(e);
                OpenLayers.Util.getElement("coords").innerHTML = 'MOUSE POSITION '+position;
                var lonlat = map.getLonLatFromPixel( this.events.getMousePosition(e) );
                OpenLayers.Util.getElement("lonlatTG").innerHTML = 'lonlat => '+lonlat;
                var lonlatTransf = lonlat.transform(map.getProjectionObject(), proj4326);
                OpenLayers.Util.getElement("lonlatTrans").innerHTML = 'lonlatTransf => '+lonlatTransf;
                OpenLayers.Util.getElement("lonlatDouble").innerHTML = 'lonlat => '+lonlat;
            });

            map.events.register("click", map, function(e) {
                var position = this.events.getMousePosition(e);
                var icon = new OpenLayers.Icon('http://maps.google.com/mapfiles/ms/icons/red-pushpin.png');   
                var lonlat = map.getLonLatFromPixel(position);
                var lonlatTransf = lonlat.transform(map.getProjectionObject(), proj4326);
                alert ('lonlatTrans=> lat='+lonlatTransf.lat+' lon='+lonlatTransf.lon+'\nlonlat=>'+lonlat+'\nposition=>'+position);
                var lonlat = lonlatTransf.transform(proj4326, map.getProjectionObject());
                var markerslayer = new OpenLayers.Layer.Markers( "Markers" );
                markerslayer.addMarker(new OpenLayers.Marker(lonlat, icon));
                map.addLayer(markerslayer);
            });
            map.addControl(new OpenLayers.Control.LayerSwitcher());
        }
    </script>
  </head>  

  <body onload="init()">
    <h1 id="title">MousePosition Control</h1>
    <div id="tags">coordinate</div>
    <p>Click on map and create marker</p>
    <div id="map" class="smallmap"></div>
    <div id="coords"></div>
    <div id="lonlatTG"></div>
    <div id="lonlatTrans"></div><br/>
    <p>
    see how, even though we did NOT transform [lonlat],
    <br/>it was nevertheless transformed
    </p>
    <div id="lonlatDouble"></div>

  </body>
</html>

there is something that you need to be aware of regarding the TRANSFORM method for LonLat as used in this simple example: when you apply [ .transform(projection1, projection2) ] to any LonLat, ALL LonLat objects are transformed.

play around with the order of certain commands and you will see what i mean.

Upvotes: 0

drnextgis
drnextgis

Reputation: 2224

Don't need to transform x and y coordinates separately. You should make clone of feature or feature's geometry and transform geomety. For example:

point_transformed = feature.clone().geometry.transform(epsg900913, epsg4326);

See code here.

Upvotes: 3

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