[OpenLayers-Users] Overlay and BaseLayer problem

[Christian Braun]

Thx very much, this solved my problem!

cheers,
Christian

On Wed, 2008-06-25 at 16:27 +0200, Eric Lemoine wrote:
> On Wed, Jun 25, 2008 at 2:36 PM, Christian Braun
> <christian.braun at tudor.lu> wrote:
> > Hi List,
> 
> Hello,
> 
> 
> 
> > I am just starting with OpenLayers and I am a looser ;-) in Javascript,
> > so please be patient.
> >
> > I want to overlay different png images in a rudimentary map. Therefore I
> > created the following code embedded in my standard html:
> >
> >  var map;
> >            function init(){
> >                map = new OpenLayers.Map ("map", {
> >                controls:[
> >                    new OpenLayers.Control.Navigation(),
> >                    new OpenLayers.Control.PanZoomBar(),
> >                    new OpenLayers.Control.Attribution(),
> >                    new OpenLayers.Control.MousePosition(),
> >                    new OpenLayers.Control.ScaleLine(),
> >                    ],
> >                numZoomLevels: 5,
> >                maxExtent: new OpenLayers.Bounds(57500, 57500, 106600,
> > 101800),
> >                maxResolution: 'auto',
> >                units: 'm',
> >                projection: new OpenLayers.Projection("EPSG:2169")
> >                } );
> >
> >                layer1 =
> > newOpenLayers.Layer.Image('LAN1','/lan_output/schedule_baseline_normal_weather/schedule_baseline_normal_weather_L_den.png',
> >                                new OpenLayers.Bounds(57500, 57500,
> > 106600, 101800),
> >                                new OpenLayers.Projection("EPSG:2169"),
> >                                new OpenLayers.Size(491,443)
> >                                );
> >
> >                layer2 = new OpenLayers.Layer.Image(
> >
> > 'LAN2','/lan_output/schedule_baseline_normal_weather/schedule_baseline_normal_weather_L_day.png',
> >                                new OpenLayers.Bounds(57500, 57500,
> > 106600, 101800),
> >                                new OpenLayers.Projection("EPSG:2169"),
> 
> The third argument should be the size. Furthermore you don't need to
> pass a projection object to the layer as it's already set in the map
> options.
> 
> >                                new OpenLayers.Size(491,443)
> >                                );
> >            map.addLayers([layer1, layer2]);
> >            map.addControl(new OpenLayers.Control.LayerSwitcher());
> >            map.zoomToMaxExtent();
> >
> >
> >
> > I want to show the images as overlays rather than with an "or" checkbox.
> 
> So you don't want your image layers to be "baselayers", you want them
> to be "overlays". To make them overlays you need to set the
> isBaseLayer option to false:
> 
> layer2 = new OpenLayers.Layer.Image(
>     'LAN2',
>     '/lan_output/schedule_baseline_normal_weather/schedule_baseline_normal_weather_L_day.png',
>     new OpenLayers.Bounds(57500, 57500,  106600, 101800),
>     new OpenLayers.Size(491,443), {
>         isBaseLayer: false
>     }
> );
> 
> That being said, it is to be noted that OpenLayers works with at least
> one base layer. If you don't want really need one you can create a
> fake one using:
> 
> var fake = new OpenLayers.Layer('fake', {displayInLayerSwitcher: false});
> map.addLayer(fake);
> 
> > Furthermore a need a flag to set transparency of some png's.
> 
> It seems to me that either your png images are transparent or they
> aren't. OpenLayers can't help you with that.
> 
> Hope this helps,
> 
> --
> Eric