tlaronde@polynum.com wrote (Mon, Nov 27 2006 08:24:51):
Thierry (CCing Hamish),
Thanks for trying to help but your analysis is mostly worng. Please read below.
FWIW, it seems clear that the problem is a snapping one, that is that a
node, whose coordinates appear to be the very same as a previous node
entered is _not_ snapped and is created as a new node.
But yes *it is snapped*. Otherwise the boundary would not be closed, and there
would be no area - while there is:
$ v.info -t ditch_1205
nodes=4
points=0
lines=0
boundaries=3
centroids=1
areas=1
islands=1
faces=0
kernels=0
primitives=4
map3d=0
And the bug is that this topological area is not buffered properly, unless I
disjoin it's boundary and join it back.
Hence even if visually the area edges are connected, they are not
But yes *they are connected*; the picture [4] shows that (ditch_1205 in
v.digit, before any edit). The picture [5] shows what the colors in v.digit
would be if the boundaries would be not connected.
since they end with distinct nodes (that are equal but not identical).
I suspect that the offending node is:
600727.68682251 5677973.32091602
In what sense? All nodes coordinates are identical in vectors ditch_1205 and
ditch_1205_edt (see my previous message to learn how they were created). Only
the sequence of of boundaries is different between the 2 vectors.
I imagine that with the new vector engine you still have a '-s' option
to v.support(1) or equivalent.
v.clean tool=snap
Take the non working case, and before buffering snap nodes with a very
small threshold. The problem shall disappear (this is indeed what you do
in v.digit(1), except that for v.digit(1) the snapping threshold is
usually relatively high).
Wrong. It doesn't help, and doesn't change anything in the data. And that's as
expected, because all nodes are already snapped in the problematic vector
ditch_1205, like I wrote above.
[4]http://kufaya.googlepages.com/ditch_1205_edt1.png
[5]http://kufaya.googlepages.com/ditch_1205_edt2.png
Maciek
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