[GRASS-user] v.net.path problem(output seem to be airline distances instead of rout distances with multiple input points)

[Stefan Neumeier]

  Dear all,

I am relatively new to GRASS so maybe I am just missing some important 
step in between.
What I want to do is to calculate a "simple" distance matrix from x 
start points (polygon-raster centroids)
to x end points (specific locations e.g. hospitals) based on a route 
network.

In a first step I prepared the network so that every start- and end 
point lies on the network (via v.net, option connect).
In a second step I created a point input textfile to use in v.net.path 
(ID startX startY endX endY) wit several thousand records.

Testing the shortest path calculation for one, two or three coordinate 
pairs read in from the point input file works
as one would expect and I get a new vector layer depicting the pathes 
from the start points to the end-points based on the
road network.

But if the number of points in the input point file exceeds 4 coordinate 
pairs GRASS  calculates all consecutive
distances seemingly as airline distances instead of road based distances 
(In the output vector layer the pairs of points
are connected with a straight line only).

Is this a known bug and if yes does anyone of you know a feasible work 
around? I would appreciate any hints/
solutions to the problem.

My system environment:

Windows xp professional
Qgis 1.5.0 with grass 6.4 (grass wxphyton interface)


Best regards,
Stefan Neumeier

-- 
Dr. Stefan Neumeier (Dipl.- Geogr.)
Institut für Ländliche Räume / Institute of Rural Studies

Johann Heinrich von Thünen-Institut (vTI),
Bundesforschungsinstitut für Ländliche Räume, Wald und Fischerei /
Johann Heinrich von Thünen-Institute,
Federal Research Institute for Rural Areas, Forestry and Fisheries
Bundesallee 50
D-38116 Braunschweig
Tel.: ++49 (0) 531 596 5241
Fax:  ++49 (0) 531 596 5599

Tel. Institutssekretariat: (+49)531-596-5502