I have a definition of 3 polygon
centroid types here (shifted centroid,
geometric centroid, visual centroid):
Some more examples and some rules to determine the
best choice of centroid for labelling, including calculation of the principal
axis for alignment:
The region geometric properties functions are
free-use and available from a button pad:
The primary use of the alternative centroids noted
in spatialSQL is to find valid alternative points for labelling. As can be seen
in the examples the choice of one type only would not produce the best
results. All computed values are stored in columns in
the target table.
There are application areas where the geometric
centroid or visual centroid could be of use in their own right. The visual
centroid is computed with an output radius of the "largest circle
to fit" and thus could be used in an SQL to determine that a chosen
polygon and v. centroid satisfy a "minimum distance to neighbour" criteria
(habitat?, agriculture?)
Regards,
Phil Waight.
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