wow. i'll have to sort through this. i have been working on network analysis too. i'll be glad to help where i can, but i'll have to digest all the info first.<br><br>one of the big problems i ran into was running v.clean
with a tolerance. apparently that would not split at the lines after doing a v.distance to the streets. so i had to go to each street connection and verify that there was in fact a node for the connectors (v.distance) out put to the streets. in many instances there were not, so i had to split the street line there and
v.clean again. I talked with Markus about this, and the only difference was that he had run his without specifying a threshold for v.clean while using the tool=break,snap. it looks like you did the same thing.<br><br>i would spot check some connections and make sure that nodes exist and that the connectors are infact connected via nodes for proper topology.
<br><br><div><span class="gmail_quote">On 8/2/06, <b class="gmail_sendername"><a href="mailto:andrew.haywood@poyry.com">andrew.haywood@poyry.com</a></b> <<a href="mailto:andrew.haywood@poyry.com">andrew.haywood@poyry.com
</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div>
<br><font face="sans-serif" size="2">Dear all,</font><br><br><font face="sans-serif" size="2">I am a new person to grass and am having
some problems with running a simple network analysis. If anybody can help
me it would be greatly appreciated. I am running grass 6.0 on debian.</font><br><font face="sans-serif" size="2">I have imported a shapefile representing
5km grid polygons across a large area. I have also imported a road shapefile
within this grid. And have imported a point shapefile with town locations
close to this road (network).</font><br><br><font face="sans-serif" size="2">What I would like to do for each centroid
of my 5km grid polygon layer is to calculate the nearest straight line
distance to the road feature. Once having calculated this distance - calculate
the distance along the road network to each town. Below is my attempt at
doing this. Any help/suggestions on improvement would be greatly appreciated.</font><br><br><font face="sans-serif" size="2">I am having problems making sure that
my town locations are on my road network and that the road network is complete.
I think that the road network is made up of line segments that are not
quite connected so I have tried v.clean to "buffer the roads toegther".
Any suggestions on how to ensure that the lines are connected would be
greatly appreciated. The following are a list of commands that I am currently
using. My problem is that my network is not connected.</font><br><br><font face="Courier New" size="2">#v.in.ogr dsn=/home/andrew/rast.shp
output=rast min_area=0.0001 snap=-1</font><br><font face="Courier New" size="2">#v.in.ogr dsn=/home/andrew/road_seg.shp
output=road_seg min_area=0.0001 snap=-1 </font><br><font face="Courier New" size="2">#v.in.ogr dsn=/home/andrew/towns.shp
output=towns min_area=0.0001 snap=-1 </font><br><br><font face="sans-serif" size="2">I then try and convert the road segments
into connected lines </font><br><font face="Courier New" size="2">v.build.polylines input=road_seg output=road
</font><br><br><font face="sans-serif" size="2">I then try and intersect the towns and
the roads together </font><br><font face="Courier New" size="2">v.patch in=road,towns out=road_towns</font><br><br><font face="sans-serif" size="2">I then connect the towns and the roads</font><br><font face="Courier New" size="2">
v.distance -p from=towns to=road output=road_towns_connect
upload=dist column=dist</font><br><br><font face="Courier New" size="2">#patch connecting line with roads and
towns</font><br><font face="Courier New" size="2">v.patch in=road_towns_connect,road_towns
out=pre_network_road_towns</font><br><font face="Courier New" size="2">v.db.connect road_towns dr=dbf data='$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/'
table=road layer=1 key=cat</font><br><font face="Courier New" size="2">v.db.connect road_towns dr=dbf data='$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/'
table=towns layer=2 key=cat</font><br><font face="Courier New" size="2">v.clean in=pre_network_road_towns out=network_road_towns
tool=break,snap</font><br><br><font face="Courier New" size="2">#add columns to rast polygon</font><br><font face="Courier New" size="2">echo "ALTER TABLE rast ADD COLUMN
from_cat integer" | db.execute</font><br><font face="Courier New" size="2">echo "ALTER TABLE rast ADD COLUMN
dist double" | db.execute</font><br><font face="Courier New" size="2">echo "ALTER TABLE rast ADD COLUMN
to_x double" | db.execute</font><br><font face="Courier New" size="2">echo "ALTER TABLE rast ADD COLUMN
to_y double" | db.execute</font><br><br><font face="Courier New" size="2">#need to run distance command</font><br><font face="Courier New" size="2">v.distance from=rast to=network_road_towns
from_type=centroid to_type=line from_layer=1 to_layer=1 dmax=-1 upload=cat,dist,to_x,to_y
column=from_cat,dist,to_x,to_y </font><br><br><font face="Courier New" size="2">#spit out to_x to_y coordinates of
intersection with network_towns_points</font><br><font face="Courier New" size="2">v.db.select map=rast layer=1 fs="|"
-c > xy_info_on_network</font><br><font face="Courier New" size="2">#spit x and y corrdinates of intersection
to a flatfile</font><br><font face="Courier New" size="2">awk < xy_info_on_network -F"|"
'{ print $9,$10}' > xy_on_network</font><br><font face="Courier New" size="2">#remove duplicates in file (I think
there are ??? points in the intersection)</font><br><font face="Courier New" size="2">sort xy_on_network > xy_on_network_sort</font><br><font face="Courier New" size="2">uniq xy_on_network_sort > xy_on_network_uniq
</font><br><font face="Courier New" size="2">v.out.ascii input=towns output=xy_towns
format=point </font><br><br><br><br><font face="sans-serif" size="2">I then sucked the points of intersection
with the road network (xy_on_network_uniw) and the town locations (xy_towns)
into a perl script and spat out a big file that looked like this to loop
through each raster centroid intersection with the network and the location
of the town.</font><br><br><font face="sans-serif" size="2">echo "1 574705.304072 9192756.736556
574705.30421218 9192756.73643771 " | v.net.path network_road_points
out=mypath nlayer=1</font><br><font face="sans-serif" size="2">v.db.select map=mypath layer=1 fs='|'
>>fun</font><br><font face="sans-serif" size="2">g.remove vect=mypath</font><br><font face="sans-serif" size="2">echo "2 574705.304212 9192756.736438
574705.30421218 9192756.73643771 " | v.net.path network_road_points
out=mypath nlayer=1</font><br><font face="sans-serif" size="2">v.db.select map=mypath layer=1 fs='|'
>>fun</font><br><font face="sans-serif" size="2">g.remove vect=mypath</font><br><font face="sans-serif" size="2">...</font><br><font face="sans-serif" size="2">...</font><br><font face="sans-serif" size="2">...</font>
<br><br><font face="sans-serif" size="2">when I run this i get errors (on some
but not all v.net.path calls) basically saying that the node cannot be
found and reports a very big distance as a default. I have started to look
at the network and i think it is because I havent closed it properly. Any
help with regard to this. Also im thinking that it may be the accuracy
of the xy locations in ascii dumps. Im not sure if I could use node id's
and that would be better. Again any suggestions would be appreciated.</font><br><br><font face="sans-serif" size="2">cheers</font><br><br><font face="sans-serif" size="2">Andy</font><br><br><br><br>
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Thank you.<br>
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