Hi Larry,
I was using "intersect", and I tried "crosses", but that didn't work.
I'm taking a look at relate now, although I'm having a hard time
deciphering DE-9IM.
I agree it is not very intuitive.
To solve the problem for homogeneous geometries (same dimension), I
would try the folowing
- for linestring : create relation if linestrings intersect in any way
to try to have different colors either if lines touch, cross or overlap
each other
- for polygons : create relation if polygon interiors intersect in any
way (overlap, include, is included : |T********|) or if boundaries
intersection has dimension 1 (|****1****|), excluding polygons touching
at one or several points.
For heterogeneous geometries, intersects is probably a good guess
...until Jukka find a counter-example :-)
Michaël
-lreeder
On Sat, Sep 20, 2014 at 1:38 PM, Michael Michaud
<m.michael.mich...@orange.fr <mailto:m.michael.mich...@orange.fr>> wrote:
Hi Larry,
Do you compute relations between geomeries with intersect predicate ?
I wonder if you could remove edges between polygons adjacent at
one point
from the graph by using relate operator (which makes it possible
to check
intersection dimension).
Michaël
Hey Jukka,
Just got a chance to look at this. The region that is not
coloring is interesting.
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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