I tried using the new algorithms and they were better for Alaska,
but I really don't like what they do to other state placements (screenshot).
I went back to some older versions of the shape files and saw that a
month ago Alaska was labeled correctly, so I'm asking my GIS guy to
see what he can do with the shapes file. Sometime in his editing,
something went wrong.
Thanks for your help. I think we'll be good to go.
- Ellis
-------- Original Message --------
Subject: Re: [Mapnik-users] Misplaced polygon labels
From: Dane Springmeyer <[email protected]>
To: Ellis Miller <[email protected]>
CC: [email protected]
Date: 11/22/2011 2:40 PM
On Nov 22, 2011, at 12:28 AM, Ellis Miller wrote:
Thanks so much!
Comments below.
-------- Original Message --------
Subject: Re: [Mapnik-users] Misplaced polygon labels
From: Dane Springmeyer <[email protected]>
To: Ellis Miller <[email protected]>
CC: [email protected]
Date: 11/22/2011 12:55 PM
On Nov 21, 2011, at 10:28 PM, Ellis Miller wrote:
Hi Ellis,
We are using
Mapnik for data mapping of demographic data
cool :)
It's been fun working with maps. When I showed the feature
to my 9-year-old son, he started playing with the various
demographic maps for a while and ended up with a comment
"I'd enjoy programming something like this!" The next day he
wanted to run the maps again. :-)
Rock on.
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'd be interested in pursuing #2.
Didn't see that coming :)
We are compiling in C++,
though it wasn't easy at first!
lol
When were the new
algorithms introduced? I think we're using 0.7.1, but
hopefully it won't be too bad to upgrade to 2.0.0.
Or just backport them first just to make sure they do what
you need. There is nothing that needs to be specific to Mapnik
2 about them. Some stuff changed around how we store
geometries in Mapnik 2, so they would not be a simple copy and
paste, but should not be too bad:
Just note - they are not used anywhere yet and only very
lightly tested.
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
|
