Andy Allan wrote:
On Sun, Apr 27, 2008 at 4:58 PM, Hendrik Siedelmann
<[EMAIL PROTECTED]> wrote:
2008/4/27 Marcus Wolschon <[EMAIL PROTECTED]>:
> | Nodes can still be identified by their lat/lon coordinates. As nodes
> | are not duplicated in the database this is possible. And routing still
> | needs to find which ways reference a node, so routing from one way to
> | another is still complicated. On the other hand checking if another
> | way uses the same points is fast on a spatial database (I will at some
> | time provide funktions provide routing)
...
> So the system cannot know the difference between 2 ways sharing the same
> node and 2 ways with 2 nodes that just share the same coordinates?
>
Yes for the database it's the same. On the other hands if two nodes
share the same coordinates they should be joined (Thats what I read),
so there will never be two nodes at the same coordinates. (At least in
theory)
This is incorrect. In OpenStreetMap two nodes can share the same
coordinates, and each belong to a separate way. This does *not* imply
that the ways are connected - in fact, quite the opposite. This is why
ways reference nodes, not coordinates.
One simple example for this are double-decker bridges. Two points on
different decks can have the same lon/lat coordinates, but they
represent different points in the 3D space, so you cannot assume the
ways are connected.
Igor
--
http://igorbrejc.net
|
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