[pgrouting-users] Wrong results at routing by choosing wrong start/end points?

[Marco Lechner - FOSSGIS e.V.]

Hallo Kai, hi list,

because I'm trying to enhance our pgrouting-based Routing-application I
took a look at these webpages, because they fit our needs (1. clicking
somewhere on the map to set start and endpoint, 2. finding the nearest
points on the routing network, 3. calculating the shortest path from
start_on_road to end_on_road:
http://pgrouting.postlbs.org/wiki/LoadingtheCode3 and
http://pgrouting.postlbs.org/wiki/LoadingtheCode4

Using the code on "LoadingtheCode4" to fill the gaps between the routing
result on "LoadingtheCode3" is good. But one question appeared:
are the start- and endpoints calculated on "LoadingtheCode3" really on
the shortest path from my_start_point to my_end_point?
The routing is calculated by using the nearest edge from the clicked
my_start|end_point. But because the real start- and endpoints are a
distance away from the start|end_on_road this could modifiy the result
in choosing a short , but not the shortest way.

See attached sketch for explanation. Am I getting anything wrong or is
this really an "error"?

Marco

-- 
+++++++++++++++++++++++++++++++++

FOSSGIS e.V.
die unabhängige Hilfe bei freier GIS-Software und freien Geodaten
www.fossgis.de

+++++++++++++++++++++++++++++++++
-------------- next part --------------
A non-text attachment was scrubbed...
Name: routing_error_01.gif
Type: image/gif
Size: 18977 bytes
Desc: not available
Url : http://lists.osgeo.org/pipermail/pgrouting-users/attachments/20091023/8f6c1a65/routing_error_01.gif