[ka-Map-users] Repeated labels on a polygon layer
dbadke at uvic.ca
Wed May 31 18:27:44 EDT 2006
Thanks for the explanation and suggestions. At least I know it's not my
fault! It explains why the repeat pattern depends on zoom level; if the
feature as rendered is small enough, it fits on a single meta-tile.
I will try the meta-tile route, and if that fails, try creating a point
shapefile for the labels.
Paul Spencer wrote:
> this is a side-effect of creating tiles. The issue is that mapserver
> has no way to deterministically place labels on tiles or to retain
> some knowledge that a label was already placed on an adjacent tile.
> We try to work around this as best as possible by rendering a
> 'meta-tile' which is essentially a much larger map draw which is then
> sliced into smaller tiles that are actually served to the client.
> This just reduces the number of times the problem occurs, it doesn't
> eliminate it.
> The only advice I have right now is to try increasing the size of the
> meta tile that you are creating. You do this by modifying config.php
> and changing the metaWidth and metaHeight variables.
> You need to be careful that the number of tiles wide/high times the
> size of each tile does not exceed mapserver's compiled-in limit for a
> single map draw (typically 2000x2000 I think).
> Also, you need to be aware that larger map draws take more time. If
> you are in a position to compile mapserver and change this limit (or
> can find someone to do it for you) and/or are willing to spend time
> pre-generating maps, then the best-case solution right now is to jack
> up the sizes to some large numbers and pre-generate all the tiles.
> I am not aware of any effort to help out label placement for tiled
> viewers, nor of any decent way of addressing the problem in mapserver.
> Actually, there is one way you could do it I think, which would be to
> pre-process all your labels into a separate point shape file with
> attributes. I'm not a gis guy, but I think this must be possible
> (although you may need something commercial to do it).
> It may be more possible to write a utility for mapserver to do this by
> walking through every layer with labels and getting each feature (and
> the extents of the feature) and having mapserver return the location
> that it would render the label at if the entire feature were visible,
> then storing that location and associated text in a separate shape
> file. This would work for static data, but not for dynamic data
> Perhaps something like this could be used in mapserver itself when
> On 31-May-06, at 3:09 PM, David Badke wrote:
>> I have a map with two polygon layers. Two other annotation layers
>> label the polygons. This all works, except that the labels repeat -
>> each polygon has the same label, in different places, two or more
>> times. In some cases one of the repeated labels isn't even on the
>> polygon, and none of the labels are where I wanted them (POSITION
>> UL). I have tried changing the annotation layers to point or polygon
>> layers - doesn't help. The layer data is all in shapefiles (except
>> the base layer).
>> So is this a ka-Map problem, a MapServer problem, a data problem, my
>> problem, or what? Anyone have any idea how to make it stop doing this?
>> You can see an example at
>> Zoom in to 50% (the middle block in the zoom widget).
Humanities Computing and Media Center
University of Victoria, BC, Canada
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