On Nov 21, 2011, at 10:28 PM, Ellis Miller wrote: Hi Ellis,
> We are using Mapnik for data mapping of demographic data cool :) > and are having a bit of a problem with the placement of Alaska's label for > our State shapefile (it's showing up in California!). Sorry about that. MultiPolygons are bit tricky and we've only recently started to work on getting placement more robust for them: https://github.com/mapnik/mapnik/issues/812 > I think it may be a problem in the shapefile, but I don't know how to fix it. Unlikely a problem in the shapefile, but nevertheless it needs to be fixed in the shapefile. > I've been a developer for quite some time, but I'm new to the GIS world. > When displaying the shapefile in Quantum GIS, it is displayed correctly: > Quantum GIS.png > When displaying the shapefile using Mapnik, the label is in CA: Mapnik.png > I could provide the shapefiles we are using -- these are based on public > shapefiles, but were edited by a GIS guy (primarily moving AK, HI, PR > and merging polygons so that we get a single label per state). > We are using mapnik in a C++ dll (see code snippet below). > The label was positioned correctly in Mapnik before the GIS guy merged > polygons. > Right, it is the merging that throws off the default centroid algorithm in mapnik. So, your options are either: 1) break back out the polygons, or at least one. You could potentially leave all of the sub parts of alaska merged except break out just the large main landmass. Add a column to the attributes that indicate you want it labeled and then filter on that attribute, using a mapnik Filter in your rule to catch only that row (representing the big polygon you want labeled) 2) Tweak include/mapnik/geometry.hpp to use a different centroid algorithm that supports multi-geometries better. Depending on your mapnik version there may be a few already available in the code you could use (the change would need to be made in src/agg/process_text_symbolizer.cpp to reroute to use them). Since you mention you are on windows I presume that tweaking and recompiling mapnik may not be in your cards, so let me know if I can help you with option #1 a bit more. > I spent a bunch of time reading forums. I found a suggestion on > http://lists.berlios.de/pipermail/mapnik-users/2011-July/004437.html to use > placement="interior", however, in C++ I don't see any Interior options for > set_label_placement. > That was only added in the Mapnik 2.0.0 release. Anyway, it also suffers from not being robust in the face of multigeometries. > Any suggestions what I should change on my side or how to track down the > problem in the shapefiles? > Thanks, > Ellis Miller > > > Code snippet for setting labels: > rule_type vTextRule; > text_symbolizer vTextSymbolizer((LPCTSTR)sColumnInDBFForShowLabel, > (LPCTSTR)sFontName_c, iFontSize, color(0, 0, 0)); > vTextSymbolizer.set_avoid_edges(true); > vTextSymbolizer.set_label_placement(POINT_PLACEMENT); > vTextRule.append(vTextSymbolizer); > > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users
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