[OpenLayers-Users] map resolutions and layers resolution

[Guillaume Sueur]

This is a great piece of information. Thanks Chris.

Christopher Schmidt a écrit :
> On Wed, Sep 10, 2008 at 11:32:27AM +0200, Guillaume Sueur wrote:
>> Hi,
>>
>> It seems that when layer's minResolution and maxResolution are set, the 
>> map's resolution are overriden and goes then from maxResolution to 
>> minResolution by x2 steps.
>> Is it a normal behaviour or am I missing something ?
> 
> This is normal behavior.
> 
> OpenLayers has two different kind of layes: Base Layers, and Overlays.
> Base layer resolutions control the resolutions available to the map:
> when the base layer is switched, the available resolutions to zoom to
> change. 
> 
> Overlays don't really care about hteir 'list' of resolutions: this list
> is *only* used to determine whether a layer is in range or not. (In 2.7,
> unless you pass layer-related resolution options *explicitly*, a layer
> is always in range; this is a break from the past.) 
> 
> The map resolution options are used as a fallback to the layer
> resolution options. When creating a layer, the initResolutions function
> loops through all the resolution-relate properties, checking first if
> the layer has such a property, then checking if the map has such a
> property. In this way, it creates a 'complete' hash of all the
> resolution related options.
> 
> It then acts as if the layer has passed all those resolution options in
> directly -- so, the map resolution parameters are just a fallback, which
> is overridden by the layer.
> 
> So, it is completely expected behavior that a layer will take the
> feedback from the map, override it with its own settings, and call it
> done.
> 
> An easy way to prevent misbehavior is to simply always pass a list of
> resolutions into your layer. Resolutions are the 'core' res properties
> in OpenLayers, and override naything else set on the map or layer. you
> don't *need* to go this far -- OpenLayers does a fair amount for you --
> but if you do that, you can never go wrong.
> 
> (This isn't the first time a resolution-related question has been asked
> which demosntrates a lack of understanding of this phenomen; This is
> just a general response to the more general qustions we get.)
> 
> Regards,