[OpenLayers-Users] zIndexing across multiple vector layers

[Andreas Hocevar]

Hi,

On Tue, Feb 17, 2009 at 11:26 AM, dalsinao <dalsinao at yahoo.es> wrote:
> Ok, here is what happens in my case:
>
> I get two layers from a WFS server on my map (let's say layer_A and
> layer_B). These layers contain point geometry features that I display on the
> map using an external graphics.
> I have added the singleroot patch (ticket #1666) to be able to select
> features from any of these WFS (vector-based) layers. When a feature is
> selected, I open a separate window showing the feature properties.
>
> It happens in some occasions that features from layer_A and features from
> layer_B are at the exact same location.
> For these situations, I've added some code to create a popup menu that
> appears on right-click and allows the user to choose which feature he/she
> wants to check (the features to choose from may belong to layer_A or
> layer_B).

Wait: the SVG/VML event model will just return the feature that is on
top. So what you are doing here must be something like in the
selectBox method of Control.SelectFeature.

> When a feature is selected, I want the externalGraphic used to display the
> feature to be moved forward, so the user can see the one that is selected.
> In this cases, playing with the z-index does not help, since the features
> may belong to different overlays.

At this point you already know which feature is selected. I see two
ways to bring it to the top:
 * determine the layer (feature.layer) and move the layer on top of
the other (e.g. using map.raiseLayer)
 * move the selected feature to a separate (temporary) layer which is on top

> So, this is my question. What should I do in order to put features from one
> layer on top of features from another one? Both layers are of
> OpenLayers.Layer.WFS type, and I have applied the singleroot.5.patch to the
> OL source code.

You cannot move layers from one layer on top of another layer without
changing layer order or moving the feature to a layer above.

An alternative would be to merge both WFS data sources into one layer.

Andreas.

> I hope that this makes the context clear.
>
> Thanks a lot for your help!
> Cheers,
> David
>
>
> Andreas Hocevar-2 wrote:
>>
>> Hi,
>>
>> On Mon, Feb 16, 2009 at 2:57 PM, dalsinao <dalsinao at yahoo.es> wrote:
>>> I want to be able to change the z-order of features on Vector layers. I
>>> have
>>> checked this Z-Index ordering example (ordering.html) and it works when
>>> you
>>> are dealing with a single Vector layer; however, I have more than one
>>> vector
>>> layer and it may happen that features from different layers are located
>>> one
>>> on top of the other.
>>
>> That's the concept of a layer. Layers are like a stack of paper
>> sheets. You can have only one sheet on top, but if your sheets are
>> transparent, only parts of sheets lying below will be obscured.
>>
>>> In these cases I want to be able to change the feature displayed on top,
>>> regardless of which layer the feature belongs.
>>
>> Then you have to make sure your features are all on the same layer.
>> There are several ways for populating a vector layer with features
>> from many sources, and you can even group them by setting feature
>> attributes.
>>
>>> I have tried playing with the graphicZIndex, but it only seems to affect
>>> features on the same layer and it does not help to go on top of features
>>> in
>>> separate layers.
>>
>> This is by design.
>>
>> If you can give us a bit more context of your application, it will be
>> easier for us to give you an advice how to solve your problem.
>>
>> Regards,
>> Andreas.
>>
>> --
>> Andreas Hocevar
>> OpenGeo - http://opengeo.org/
>> Expert service straight from the developers.
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>>
>>
>
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-- 
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.