Hi Larry,
Version 0.5 colors now all the Finnish municipalities and all the multi-slice
pizzas which I digitized fine. However, I think that when there are at maximum
5 areas touching on one point the version 0.4 does better coloring. The new
version may give the same color for areas which touch on one point even it
would not be necessary. My municipality map seems to be a good test dataset
because it has a) multipolygons where the parts are touching on one point ->
parts should be painted with the same color and b) separate simple polygons
touching on one point -> would be better to paint with different colors if
possible.
If I had to select between 0.4 and 0.5 I think I would select 0.4 because of
the better coloring result in normal cases.
I prefer to keep the lib\ext folder a bit more clean by copying only
ojmapcoloring.jar there and putting the rest of the package into folder
lib\ext\ojmapcoloring-0.5. Perhaps it is still not worth changing the packaging
or installation instructions.
-Jukka Rahkonen-
Larry Reeder wrote:
Well, no matter how many times you slice it, a pizza is always (mostly) planar
:-). The problem with map coloring occurs when you can't draw a line on a
plane from a fixed point on all features to a fixed point on their adjacent
features without the lines crossing. You have to lift the lines off the plane
to connect adjacent features, so the adjacency graph becomes non-planar.
I've got a fix for it now, one that doesn't count features touching on a point
as adjacent. Give it a try -
https://sourceforge.net/projects/ojmapcoloring/files/0.5/
-lreeder
On Mon, Sep 22, 2014 at 4:09 AM, Rahkonen Jukka (Tike)
<jukka.rahko...@mmmtike.fi<mailto:jukka.rahko...@mmmtike.fi>> wrote:
Hi Larry,
I should have actually guessed what happened. There used to be 8 municipalies
sharing a common landmark but because of some fusions there are only 6 left now.
I tried to find a document that says that pizza is no more planar when it is
sliced into 6 pieces. However, I found some documents which define the four or
five color theorem so that polygons are considered to be adjacent if they share
an edge, not only a point. This is one of those
http://www.mathpages.com/home/kmath266/kmath266.htm.
-Jukka-
Larry Reeder wrote:
Hey Jukka,
Just got a chance to look at this. The region that is not coloring is
interesting.
[cid:image001.jpg@01CFDB0D.F27F23B0]
It's like a pizza sliced into six pieces, each touching at the point. You
can't color this portion of the map with only five colors without two adjacent
(maybe just adjacent at one point in the enter) regions having the same color.
In graph-theory terms, the graph is "non-planar" and can't be colored
correctly with the five-color theorem. The map coloring plugin detects this
and refuses to color this portion of the map.
From a practical standpoint, you probably don't care that regions touching at a
single point have the same color, as long as they don't share a color along a
long edge. I'll look at updating the plugin to detect this and continue
coloring.
-lreeder
On Mon, Sep 15, 2014 at 7:15 AM, Rahkonen Jukka (Tike)
<jukka.rahko...@mmmtike.fi<mailto:jukka.rahko...@mmmtike.fi>> wrote:
Hi,
I found a shapefile from which some polygons are not colored with the Map
coloring plugin v. 0.4. Shapefile does not have topology errors but some
multipolygons have quite a many parts because of archipelago. However,
exploding multipolygons into polygons does not change the behaviour. The
problematic shapefile can be found from
http://latuviitta.org/downloads/ojmapcolor_error.zip
Error appears always in the same place in South-West. For example features with
OGR_FID=180 or 234 stays without color.
-Jukka Rahkonen-
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