[OpenLayers-Users] Resolutions with Geowebcache and WMSGetFeatureInfo [Sec=Unclassified]

[Tim Schaub]

Hi Miles-

GeoWebCache supports the WMTS standard.  The WMTS standard defines a 
GetFeatureInfo method (with different semantics than the WMS 
GetFeatureInfo method).  OpenLayers (true) provides a WMTS layer.  I've 
got a patch outstanding to add a WMTS GetFeatureInfo control.  This, in 
my mind, is the way to get feature info from a tile service.

A few tickets need addressing before this would be entirely useful to 
you.  You can watch this one if you're interested:

http://trac.openlayers.org/ticket/2678

I'll try to find some time to finish that up in the near future.

Tim

On 7/28/10 6:00 PM, Miles Jordan wrote:
> Hi Andreas,
>
> Thanks. That method works, but I was hoping I could get geowebcache
> to work so that clients that consume data from us can access both
> maps and getfeatureinfo from the one url. Ideally I would like to
> have geoserver completely inaccessible from outside the firewall,
> with geowebcache being the only way to access it. Your suggestion
> will do the trick for the time being though.
>
> Regards,
>
> Miles
>
> Andreas Hocevar wrote:
>> Hi,
>>
>> the problem I see with your approach is that
>> OpenLayers.Control.GetFeatureInfo creates a GetFeatureInfo request
>> for the map extent, not for a tile. I would recommend sending
>> GetFeatureInfo requests to the underlying WMS, as explained in
>> http://getsatisfaction.com/opengeo/topics/error_in_wmsgetfeatureinfo#r
>>
>>
eply_2612983
>>
>> Regards, Andreas.
>>
>> On Jul 27, 2010, at 08:55 , Miles Jordan wrote:
>>
>>> Hi,
>>>
>>> I've been debugging a problem that I've been having with using
>>> the WMSGetFeatureInfo control and GeoWebCache.
>>>
>>> Basically I am setting OpenLayers.DOTS_PER_INCH to
>>> 90.71428571428572
>> which is what GeoWebCache expects by default, however when the
>> WMSGetFeatureInfo request goes through to GeoWebCache it is like
>> it's using the default 72 for DOTS_PER_INCH, because all of the
>> resolutions are about 21% out.
>>>
>>> GeoWebCache responds with messages such as :"400: Requested
>> horizontal resolution: 0.54931640625 , best match: 0.703125
>> exceeds 10% threshold. Perhaps the client is configured with an
>> incorrect set of scales (resolutions), or the DPI setting is off
>> compared to the one in GWC ?"
>>>
>>> I've actually just dropped the WMSGetFeatureInfo control into a
>> GeoWebCache OpenLayers demo, so the resolutions are definitely set
>> up to match. The full source (pretty short and simple) is at
>> http://pastebin.com/JENnAPC9.
>>>
>>> I've brought it up on the GeoWebCache mailing list but now
>>> thinking that it's more likely something to do with OpenLayers.
>>> Here's a link to my messages: http://tinyurl.com/38jvcva
>>>
>>> It seems like the resolution would be calculated incorrectly by
>> about that amount if the DOTS_PER_INCH were still at 72, so I'm
>> wondering if there's another setting that I need to change or if
>> there's a bug somewhere.
>>>
>>> Your comments are appreciated.
>>>
>>> Regards,
>>>
>>> Miles Jordan Acting Manager / Systems Analyst Australian
>>> Antarctic Data Centre Australian Antarctic Division Dept. of the
>>> Environment, Water, Heritage&  the Arts
>>>
>>>
>>>
>>>
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>
>
>
> Regards,
>
> Miles
>
>
>
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-- 
Tim Schaub
OpenGeo - http://opengeo.org
Expert service straight from the developers.