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

[David D Gray]

Eric G. Miller wrote:

> [...]
> 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

I've now run your script on some files. I can't confirm that there are 
any cases of islands being incorrectly built. they all appear as I (and 
Radim) described earlier, ie. with no internal boundaries separating 
different cells, of course you may have found some.

The matter with area assignments to islands' lines is different. I 
couldn't repeat the problem you reported, but found something else 
equally bizarre:

I tested a small map with three chinese eggs, each of two segments, and 
the ouput is as follows: [going inwards]

Area 1 {
   dig_att = 0
   lines {
     line 1, left -1, right 1
     line 2, left -1, right 1
   }
   Island 2 {
     Lines {
       Line -3, LeftArea -2, RightArea 2
       Line 4, LeftArea 2, RightArea -2
     } = Area -1
   }
}
Area 2 {
   dig_att = 0
   lines {
     line 3, left -2, right 2
     line -4, left 2, right -2
   }
   Island 3 {
     Lines {
       Line 5, LeftArea 3, RightArea -3
       Line -6, LeftArea -3, RightArea 3
     } = Area -1
   }
}
Area 3 {
   dig_att = 0
   lines {
     line -5, left 3, right -3
     line 6, left -3, right 3
   }
}

All the lines here appear to have the same area on each side. So the 
assignment of left/right area seems to be getting mangled. Could this be 
giving the errors with internal boundaries, or apparent boundaries?

Anyway this definately needs looking into. It's getting late here, so it 
will have to wait till tomorrow evening now, but I'll get back if I find 
anything.

David