Hi Larry,
Nice that you found the right matrix.
When relation is commutative,
I usually use the following pattern to avoid computing twice :
if (A.getID() < B.getID()) {
if (A relate B) {
setRelation(A,B)
setRelation(B,A)
}
}
Michaël
Thanks Michaël. I'm using "FF2F01212" for polygons, which seems to
work well, and doesn't break the line or point cases. Calculating the
intersection matrix with relate was slower than just doing intersects,
but I was able to look at my algorithm and add some adjacency caching
which made the whole thing 2X faster, so all was for the best.
-lreeder
On Sun, Sep 21, 2014 at 8:15 AM, Michael Michaud
<m.michael.mich...@orange.fr <mailto:m.michael.mich...@orange.fr>> wrote:
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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