[GRASS-user] Re: Drivetime Isochrones

[Moritz Lennert]

On 16/06/11 19:54, RKiTect wrote:
> **UPDATE**
>
> Ok, so i have figured out one part of the problem. Perhaps somone can
> provide some further guideance?
>
> I have used the v.net function on my arc shapefile, using the nodes
> operation to create another shapefile with just the nodes of the network. I
> can then input into the v.net.iso tool both of these files (the arc and
> nodes layers respectivlely). up to this point i am stuck, becuae i can't
> figure out how to specifiy the centre points for the isoline calculations...
> i am thinkning i need to modify the attribute table of my nodes layer, but
> not sure how this should be done... does anyone have any experience in using
> v.net.iso in GUI format, that could help me?
>
> Any input is much appreciated.

1) Connect centre points to roads:

v.net input=roads points=centre_point output=roads_with_point 
operation=connect threshold=DistanceBetweenPointAndNearestLineInNetwork

2) Create isoline vector

v.net.iso input=roads_with_point output=isolines ccats=1-999 
costs=TheDistanceThresholds

Please be aware that this module does not create a surface, but affects 
each line of the network to one of the classes defined by your cost 
thresholds. You could possible use interpolation afterwards to create a 
surface from these lines.

Moritz