[Chameleon] adding several layers from the same external WMS

[Paul Spencer]

Bart,

there is one potentially serious side effect of this that appears to be 
a mapserver issue, which is transparency.  I have not isolated this, but 
it appears that there is a problem with transparency when requesting 
multiple layers in this way.  I am not entirely sure where I saw the 
problem but I know it was recently.  If you see anything like this, can 
you please report it ...

Paul

Bart van den Eijnden wrote:

> Hi Paul,
> 
> just to clarify things.
> 
> I have tested whether or not the Web Map Context functionality works 
> correctly with the layers=A,B,C,D,E syntax and as you said it works 
> fine. Must be an older version of Chameleon in which I saw this fail, or 
> at that time I did something wrong.
> 
> The most important thing is that the "wms_name" metadata is correct in 
> the LAYER definition ("wms_name"    "A,B,C,D,E").
> 
> So I will not file a bug for this.
> 
> Best regards,
> Bart
> 
> On Wed, 17 Dec 2003 17:47:01 -0500, Paul Spencer <pagameba@magma.ca> wrote:
> 
>> Yes, we have discussed this performance enhancement internally because 
>> of issues another client was having with performance.  The intention, 
>> I believe, is to implement the combining 'automagically' in mapserver 
>> wms client code, it would detect that more than one layer is coming 
>> from the same wms server in the same projection etc and would combine 
>> the requests if possible (i.e. if the layers are together).  I don't 
>> know if there is a bug in mapserver bugzilla on this or not, but I 
>> suspect there is ... in fact it is bug 116, and it has been marked P1 
>> for version 4.1 which means that it should get implemented in time for 
>> the next release sometime before March (hopefully).
>>
>> I have cc'd Bart on this bug.
>>
>> Re the combining of layers in a context, I know this works because I 
>> have been using it recently.  However, it does cause some funny side 
>> effects, like layer transparency doesn't seem to work correctly.
>>
>> I would recommend that you create a bug in chameleon on maptools 
>> regarding the interaction with the upload/download context and I will 
>> try to take a look at it before the release.
>>
>> Cheers,
>>
>> Paul
>>
>> Huub Fleuren wrote:
>>
>>>
>>> one of the Geodan mapswing components (the java  mApplet) uses a 
>>> combine=true setting for this purpose.
>>> the applet 'combines' a request to the server if the layers are al 
>>> from the same server url into a sigle GET request to the Geodan 
>>> mapserver
>>>
>>> in the chameleon/mapserv setup this would have to be done by the 
>>> mapserver after reading the map file
>>>
>>> Huub
>>>
>>> bartvde@xs4all.nl wrote:
>>>
>>>> Hi list,
>>>>
>>>> in Chameleon there is the possibility to add layers from a treeview 
>>>> to the
>>>> map.
>>>>
>>>> In this case if a user adds e.g. 5 layers from the same external WMS, 5
>>>> LAYERS are created in the session MAP file, all with a connection type
>>>> WMS.
>>>>
>>>> This means 5 requests to the external WMS per Chameleon MAP refresh. In
>>>> theory, this could be solved by asking just one image to the WMS server
>>>> (layers=A,B,C,D,E). Ofcourse, this has the assumption that the five 
>>>> layers
>>>> from the external WMS are in sequence on top of each other, and not 
>>>> some
>>>> other layer in between.
>>>>
>>>> I have also noticed that when using the layers=A,B,C,D,E type of 
>>>> syntax,
>>>> the Web Map Context (save, upload) does not function any more.
>>>>
>>>> Any thoughts on this, could this be a potential performance enhancement
>>>> for Chameleon, and would this require changes in PHP/Mapscript or in 
>>>> the
>>>> Chameleon PHP code?
>>>>
>>>> Best regards,
>>>> Bart
>>>> _______________________________________________
>>>> Chameleon mailing list
>>>> Chameleon@lists.maptools.org
>>>> http://lists.maptools.org/mailman/listinfo/chameleon
>>>>
>>>>
>>>>
>>>
>>
> 
> 
> 

-- 
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|Paul Spencer                           spencer@dmsolutions.ca    |
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|Applications & Software Development                              |
|DM Solutions Group Inc                 http://www.dmsolutions.ca/|
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