On 16/10/12 10:02, Markus Metz wrote:
On Tue, Oct 16, 2012 at 12:52 AM, Moritz Lennert
<[email protected]> wrote:
On 15/10/12 16:30, Markus Metz wrote:
So how does it calculate the distance between two lines (lines or
boundaries) ? Between closest vertices ? What about lines that cross
several
other lines, or lines that cross each other at several points ?
For lines to lines, say line A to line B, it calculates shortest
distance of each vertex in A with each segment (not vertex) in B. So
far, this is the same like in the original version, results are
identical.
The original version did not have line to line...
What I meant was that this is equivalent to the shortest distance of
several points to a line, regarding points as line vertices.
Ok.
Much better, thanks ! Just one issue still with the area2area case for the
test polygon with cat=2:
http://164.15.12.207/grass/v_distance_areas2.png
The connection line/point doesn't touch the the polygon in the from map.
But it is inside the polygon of the 'from' map. In this
implementation, any shared location is as good as any other.
Calculating an intersection is costlier than to check if a vertex is
inside a polygon. The vertex of the boundary of the 'to' area is
inside the 'from' area, thus a common location. For speed reasons, the
distance is set to zero and no further tests are done.
Ok, this makes it clear. Thanks !
The results can be unexpected for 'to' areas with isles, because
v.distance (in all versions) does not require a 'to' feature to have a
category, which also means that isles inside areas which themselves
can be areas without centroids are regarded as valid 'to' features,
just without category. But even though the results can be unexpected,
I would leave them as such, otherwise 'to' feature would need to have
a category, potentially leading to also different results for points
to lines which has always been supported.
Yes, that's why documentation is so important on all this.
Moritz
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