[GRASS5] Nested vector islands, and incorrect left/right poly id's for island edges...

[Eric G. Miller]

It appears that GRASS doesn't write correct information for
left/right adjaceny for edges of areas nested more than
one polygon deep.  That is: If polygon 1, contains polygon
2, and polygon 2 contains polygon 3, the lines comprising
polygon 3 will have polygon 1 written as the adjacent area
for either left or right, when I would think it should be
polygon 2.

I was trying to work up a way to do the following:

  Given an area with N islands/holes.  Create a set of
  interior boundaries such that islands/holes that
  share one or more edges are combined into a single
  boundary (with interior edges being dropped).

I tried to write a little program that iterated through
areas, and their islands, reporting the lines for all
and the reported line left/right indices.  That's when
I discovered, I was getting islands where none of the
edges reported being adjacent to their immediate parent.

I guess, next I'll try using nodes instead of edges.  If
anyone familiar with the guts of the vector libraries
(Radim, David ?) wants to point me in the right direction,
I'd appreciate it...

Attached:  area_report.c & Gmakefile

-- 
Eric G. Miller <egm2 at jps.net>
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