[udig-devel] accuracy of GetFeatureInfo

[Bart van den Eijnden (OSGIS)]

Hi Jody,

why did you end up changing the BBOX and width/height client-side? Why 
not leave it up to the WMS server like Gaia does?

Best regards,
Bart

Jody Garnett schreef:
> Indeed, we eventually figured out that WMS getInfo is considered a 
> check in the center of a single pixel.
>
> Thinking,
>
> Richard for a while we forced the renderers to leave us a hook so we 
> could make our info request, is there any way we can ask the WMS 
> renderers to leave some hints on the layer blackboard about the image 
> rendered? The same plugin making the rendering contribution can 
> provide the hint ...
>
> Jody
>> Hi Jody,
>>
>> the projections I am trying are both supported by the WMS.
>>
>> Unfortunately I have no Java hosting, but it's a simple shapefile 
>> which can be set up with Geoserver. I am using 1.4.
>>
>> The shapefile can be found here (200 Kb, native projection 
>> EPSG:28992, uDIG set to RD / New projection):
>>
>> http://www.osgis.nl/lausanne/nl-prov.zip
>>
>> An example request which uDIG is fyring off is (this request is 
>> really strange since the BBOX is not the BBOX of the map image shown 
>> anymore! and X and Y are always 1):
>>
>> /geoserver/wms?Y=1&X=1&SERVICE=WMS&INFO_FORMAT=text/html&LAYERS=ogctestbed:nl-prov&FORMAT=image/png&HEIGHT=3&REQUEST=GetFeatureInfo&WIDTH=3&BBOX=188907.50415179788,391802.21024004533,192453.4125990071,395348.1186872545&SRS=EPSG:28992&QUERY_LAYERS=ogctestbed%3Anl-prov&VERSION=1.1.1 
>> HTTP/1.1" 200 447
>>
>> Thanks in advance.
>>
>> Best regards,
>> Bart
>>
>> Jody Garnett schreef:
>>> Good question, it makes a direct call when able to make a direct 
>>> rendering of the WMS image (ie udig is using a coordinate system 
>>> supported by the WMS). In rare cases it may have to resample the 
>>> image onto the screen (making up for lack of WMS projections), we 
>>> could check that we back project the query into the coordinate space 
>>> of the original image... but as I recall I wrote this one and went 
>>> to some trouble to get it right.
>>>
>>> Can you point us at a service illustrating the problem, perhaps in a 
>>> jira report.
>>> Jody
>>>> Hi list,
>>>>
>>>> how accurate is uDIG with respect to GetFeatureInfo?
>>>>
>>>> I have tried it against 2 WMS's, Geoserver and Deegree, and at the 
>>>> borders of provinces, a lot of times the wrong element is returned. 
>>>> Ofcourse this could also be due to the WMS's.
>>>>
>>>> So I checked Gaia, and using Gaia it is very accurate for 
>>>> Geoserver, so I am assuming it is a uDIG problem.
>>>>
>>>> Any input appreciated.
>>>>
>>>> Best regards,
>>>> Bart
>>>>
>>>
>>>
>>> _______________________________________________
>>> User-friendly Desktop Internet GIS (uDig)
>>> http://udig.refractions.net
>>> http://lists.refractions.net/mailman/listinfo/udig-devel
>>>
>>>
>>
>>
>
>
> _______________________________________________
> User-friendly Desktop Internet GIS (uDig)
> http://udig.refractions.net
> http://lists.refractions.net/mailman/listinfo/udig-devel
>
>


-- 
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl