[udig-devel] accuracy of GetFeatureInfo
Bart van den Eijnden (OSGIS)
bartvde at xs4all.nl
Sun Sep 10 06:39:48 PDT 2006
I am testing this with 1.1RC4.
Strange things happen though, if I add my Geoserver WMS layer I get a
Generic Cartesian 2D CRS in the map. If I change the projection to
RD/New the coordinates end up being silly (-1, -1).
If I add my Mapserver WMS first, it starts in the correct CRS (WGS84 is
the first one advertized). Then I add Geoserver, and the layer does not
render since "Coordinate Reference System of Data is unknown".
Update: strangely enough this disappears after a restart of uDIG!
The accuracy of GetFeatureInfo seems a lot better! Good work Richard.
I was only able to test EPSG:28992 (the native projection) since
Geoserver's WMS GetFeatureInfo does not work in a reprojected CRS :-(
Best regards,
Bart
Bart van den Eijnden (OSGIS) schreef:
> Hi Richard,
>
> I can test it, no problem. My plane to Lausanne leaves only Monday
> morning :-)
>
> Best regards,
> Bart
>
> Richard Gould schreef:
>> Ok, crazy buffering removed. uDig should make sane WMS GetFeatureInfo
>> requests now. This is on trunk, and will be reflected in the release we
>> are trying to put out (later today).
>>
>> It definitely needs some testing, in particular when both client and
>> server side reprojection are involved. (The fix was written in haste and
>> may not be perfect)
>>
>> Bart, are you able to test it once we have a release ready?
>>
>> Richard
>>
>> On Tue, 2006-05-09 at 19:42 +0200, Bart van den Eijnden (OSGIS) wrote:
>>
>>> uDIG requests a 3x3 image. And then it requests the topleft pixel
>>> (X=1, Y=1).
>>>
>>> I don't know the internals ofcourse, but should it not request the
>>> center pixel (X=2, Y=2)? At least that gives the correct results for
>>> my testcase :-)
>>>
>>> Why else would it request 3x3, it might as well request 1x1 or 2x2
>>> if it is using the topleft pixel.
>>>
>>> Best regards,
>>> Bart
>>>
>>> Jody Garnett schreef:
>>>
>>>> In that case we will need to ask Richard to implement a different
>>>> plugin for the InfoTool for each renderer he creates. Not fun but
>>>> possible. I did think he ended up making a 2x2 reference image and
>>>> selecting the first pixel (after having a few WMS fail on a 1x1
>>>> image reference image.
>>>> Jody
>>>>
>>>>> I think the problem with this approach, as now demonstrated, is
>>>>> that it doesn't work :) It might take something a little more
>>>>> "arbitrary", like a pretend image of "about 300 pixels in size"
>>>>> with the click point in the "middle of that image" to get a
>>>>> correct-seeming answer. Sending back a one-pixel map with a click
>>>>> "on the pixel" is begging to hit corner cases in the WMS server
>>>>> side code.
>>>>>
>>>>> On 5-Sep-06, at 12:29 AM, Jody Garnett wrote:
>>>>>
>>>>>
>>>>>> Ah, interesting question ... because of a difference between what
>>>>>> we display and what we requested from the WMS.
>>>>>> - often we will have to make several requests and tile content
>>>>>> onto the screen in WMS happy chunks,
>>>>>> - or we will need to make slightly larger requests and resample
>>>>>> them onto the screen (as mentioned previously).
>>>>>>
>>>>>> It was just easier to back project a pixel and use it to make a
>>>>>> request in the correct location once, rather then trying to
>>>>>> reverse several rendering process es to exactly match the
>>>>>> original request (aka the approach we used for uDig 0.8).
>>>>>>
>>>>>> Cheers,
>>>>>> Jody
>>>>>>
>>>>>>> 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
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>> _______________________________________________
>>>>>> 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
>>>>>
>>>> _______________________________________________
>>>> 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
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