Hi Martin,
The following is a general algorithm query rather than a specific JTS
question - hope that's ok.
I have a set of polygons which represent urban areas within a
fire-prone landscape. There are about 5000 polygons varying widely in
area, spatial extent, number of vertices and boundary complexity.
I have the task of creating a regular grid of sample points within the
surrounding landscape and, for each point, determining the distance to
the nearest polygon within each of eight compass segments (ie. N to
NE, NE to E...). The results only need to be expressed as categorized
values based on a small number of distance cut-points.
I've been trying to nut out something other than a brute force
approach to this without much success so far. One of the possibly less
brutish approaches I've thought of involves the following:
1. Split up the urban polygons by intersecting them with a regular
lattice, create PreparedGeometry objects for the resulting parts and
put them into an STRtree.
2. Construct a sampling template made up of polygons representing the
compass segments, each split according to the distance cut-points
(looking a bit like a dart board), possibly using a custom
CoordinateSequence to have vertex coordinates calculated on the fly
based on the centre coordinate.
3. For each sample point location:
For each compass segment:
For inner to outer segment part:
Query the spatial index with the segment part envelope
and, if any urban polygons are returned, test for
intersection.
I'm sure there must be a better way. Any suggestions or comments will
be gratefully accepted.
Michael
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