No, the desire is not to provide a buffer, it is to get the right
answer :)
On 5-Sep-06, at 10:10 AM, Richard Gould wrote:
On Tue, 2006-05-09 at 17:02 +0200, Jody Garnett wrote:
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.
Err.. I made a couple experiments with this, but I didn't ever
think it
was really feasible. I think the goal was to be able to provide a
buffer
around a point clicked, or provide support for bbox-enabled
GetFeatureInfo requests (WMS spec says you can only use point
requests).
Since the info tool in uDig is point based, I presume that the
desire is
to provide a buffer? Paul is right in that shrinking the image a bit
would be closer to the desired effect. If we shrink the image to
3x3 and
ask for one pixel, we are going to get 1/9 of the screen back (and
possibly the wrong section too).
So I think we should default back to just using the standard method of
doing it (ie. let the WMS provide tolerance if it wishes). We could
add
a preference option to enable a buffer around the point and then
use the
voodoo code, but I don't think it should be a default.
I'll see if I can fix this on Thursday morning, before the RC release.
Richard
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=188907.50415179
788,391802.21024004533,192453.4125990071,395348.1186872545&SRS=E
PSG: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
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User-friendly Desktop Internet GIS (uDig)
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User-friendly Desktop Internet GIS (uDig)
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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
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