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
--
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl
_______________________________________________
User-friendly Desktop Internet GIS (uDig)
http://udig.refractions.net
http://lists.refractions.net/mailman/listinfo/udig-devel
