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
