Hi, I created a SLD in GeoServer 1.7.3 to symbolize cities in a world map with a label and a graphic point. Unfortunately, some labels don’t appear with no apparent reason. Please, see the example.
The London label will appear only after several zooms. The Paris label appears while zooming out (!) but disappears zooming in just like London. I have many of this kind of cases at any zoom levels with no other close label. Any suggestion? Is there a problem? Thanks a lot for your help! Paolo
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Paolo Pasquali ha scritto:
Hi, I created a SLD in GeoServer 1.7.3 to symbolize cities in a world map with a label and a graphic point. Unfortunately, some labels don't appear with no apparent reason. Please, see the example.
The London label will appear only after several zooms. The Paris label appears while zooming out (!) but disappears zooming in just like London. I have many of this kind of cases at any zoom levels with no other close label. Any suggestion? Is there a problem? Thanks a lot for your help! Paolo
Hum,
is that map drawn as a single image, or is it tiled?
The most common issue for labels not appearing is that the label
would have crossed the tile borders. The Paris label is probably
within the tile at a lower zoom levels, but as tiles becomes
smaller as you zoom in, it gets probably too close to a border
afterwards.
There is some discussion on why labels cannot be drawn if they
cross the tile borders here:
http://geoserver.org/display/GEOS/Rendering+and+tiling+issues+research
The usual workaround is to use a tile cache such as GWC and have it
meta-tile, that is, ask the WMS blocks of nxn tiles to be cut in
post-processing. The problem will anyways don't go away on the
meta tile borders.
Tiling and labelling with conflict resolution just don't work
well togheter, don't think anybody has found a general solution
to the problem (although I'm just guessing, I believe Google does pre
process all the label positions for all the world in one shot
for each zoom level, stores the resulting positions, hand fixes
them as needed, and then performs the drawing without conflict
resolution, assuming conflicts are already solved, and thus
can happily draw labels that do cross tile borders).
Cheers
Andrea
--
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.
That makes sense. Thank you, Andrea.
Bye.
Paolo
Andrea Aime-4 wrote:
Paolo Pasquali ha scritto:
Hi, I created a SLD in GeoServer 1.7.3 to symbolize cities in a world
map with a label and a graphic point. Unfortunately, some labels don't
appear with no apparent reason. Please, see the example.
The London label will appear only after several zooms. The Paris label
appears while zooming out (!) but disappears zooming in just like
London. I have many of this kind of cases at any zoom levels with no
other close label. Any suggestion? Is there a problem? Thanks a lot for
your help! Paolo
Hum,
is that map drawn as a single image, or is it tiled?
The most common issue for labels not appearing is that the label
would have crossed the tile borders. The Paris label is probably
within the tile at a lower zoom levels, but as tiles becomes
smaller as you zoom in, it gets probably too close to a border
afterwards.
There is some discussion on why labels cannot be drawn if they
cross the tile borders here:
http://geoserver.org/display/GEOS/Rendering+and+tiling+issues+research
The usual workaround is to use a tile cache such as GWC and have it
meta-tile, that is, ask the WMS blocks of nxn tiles to be cut in
post-processing. The problem will anyways don't go away on the
meta tile borders.
Tiling and labelling with conflict resolution just don't work
well togheter, don't think anybody has found a general solution
to the problem (although I'm just guessing, I believe Google does pre
process all the label positions for all the world in one shot
for each zoom level, stores the resulting positions, hand fixes
them as needed, and then performs the drawing without conflict
resolution, assuming conflicts are already solved, and thus
can happily draw labels that do cross tile borders).
Cheers
Andrea
--
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.
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