[OpenLayers-Dev] Base Layer vs. Main layer

Kenneth Skovhede, GEOGRAF A/S ks at geograf.dk
Wed Nov 19 14:43:03 EST 2008

Hmm... a bit counter intuitive, but I guess that would actually work.
So all layers would be "overlays" with respect to OpenLayers.

Regards, Kenneth Skovhede, GEOGRAF A/S

Christopher Schmidt skrev:
> On Wed, Nov 19, 2008 at 08:04:39PM +0100, Kenneth Skovhede, GEOGRAF A/S wrote:
>> Very nice explanations!
>> The Wiki page explains the problem quite well.
>> I wish I had found that page a long time ago.
>> Just to carve it in stone, I would like my layer stack to look like this:
>> [Vector] -> OpenLayers vector layer
>> [Selection] -> Transparent PNG, rendered dynamically by MapGuide
>> [Dynamic Overlay] -> Main layer with bounds, etc. Also displays 
>> thematics from MapGuide, eg Election districts.
>> [Base layer 1] -> Transparent PNG with things like lakes etc that are 
>> not easily visible on an aerial
>> [Base layer 2] -> Transparent PNG with things building outlines, road 
>> names etc.
>> [Base layer 3] -> Aerial JPG (opaque)
>> This enables the user to turn off building outlines without having to 
>> reload the aerial.
>> It also enables the user to toggle different thematics on and off 
>> without reloading the aerial or building outlines.
>> (It obviously costs more server calls to have the division).
>> As I see it, my "Vector" and "Selection" are clearly overlays, where as 
>> the "Dynamic Overlay" is the main layer.
>> Currently I have to assign this as the "baseLayer" because it has all 
>> the required info (units, bounds, etc.)
> Since all of these layers are in the same projectino (since OpenLayers
> has no way of doing anything else) I don't see that this is actually
> required. 
> Instead, what I would recmomed you do is simply create an empty base
> layer:
>   new OpenLayers.Layer("", {displayInLayerSwitcher:false, 
>   isBaseLayer: true,
>   maxExtent:,  maxResolution, etc.});
> This  layer would be the only base layer.
> Then, all the other layers can be used in any way you want.
> How does this not work for your situation?
>> Perhaps a real solution would be to follow the tracks of:
>> http://trac.openlayers.org/ticket/1096
>> But add a property named "isBottomLayer" instead to allow compatibility 
>> with the existing code.
> I don't understand what you mean, but I do not expect that any changes
> will be made in this regard before 3.0.
> Regards,
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