[Qgis-user] v.extract.where query

[Erica Donnelly-Swift]

Hi all,

I'm working on a road network vector file, however I have encountered   
a small issue, and I would be very grateful if you could please offer  
suggestions,
I'm unsure why this issue is arising, as I have worked with this data  
a few months ago with no problems.... any advice is greatly appreciated.
Thanks

I'm working with road collision data.... and I have a slight issue  
with excluding collisions that have been snapped >500m to a particular  
route.

The problem arises when:
I use v.extract.where in the GRASS toolbox setting Distance<500 and  
then I load the new map, a large proportion of the collisions are not  
included in this new map (I have also changed setting to have Distance  
<1000, however the same map is produced as the Distance <500m map)

  I have outlined my steps below:
(I'm working on MAC OSX 10.5.8, QGIS version 1.4.0 Enceladus)

1) Loaded road into GRASS (using v.in.ogr.qgis)
2) Loaded collisions into GRASS (using v.in.ogr.qgis)
3) Created 3 new columns (X,Y,Distance) in the collisions attribute  
table (using v.db.addcol)
4) used v.distance to calculate 'minimum distance to next  
feature' (also recorded the x,y co-ordinates in the corresponding x,y  
columns)
5) used v.extract.where setting Distance < 500 called the output  
'collisions500' and then I reloaded the collisions500

I have tried shutting down QGIS / restarting/ reloading ..... but the  
same problem still occurs....