[GRASSLIST:6661] Re: v.net.path cost function?

[Radim Blazek]

Ryan D Taylor wrote:
> Hi,
> 
> I'm just wondering what the v.net.path module uses to determine the 
> default cost of an arc.  It doesn't seem to be distance as this is the 
> shortest path it gave me between 2 nodes:
> 
> http://www.cs.utah.edu/~ryant/shortestpath.gif

Are you sure that there are no gaps in the network? Is it TIGER?
Try to test with d.path and v.digit if the lines are connected.

> Also, as some background information, this is what i've done to generate 
> the shortest path.  I started with some vector data called "slc" which 
> contains real road data, then I ran a v.net to generate a vector map 
> called "nodesmap" with the node data. then i did a v.category with  
> "nodesmap" as the input and "categorymap" as 
> the output.  Finally I did a v.net.path with "categorymap" as input and 
> "shortestpath" as the output--which you can see in red in the gif file. 
> 
> Ultimately I'm trying to determine a shortest path between two points that 
> takes into account more than distance.  My original vector data set 
> contains columns that describe speed limits, road directions, road 
> quality, etc.  How could I get v.net.path to take several fields like that 
> into account?  Also, since I'm generating the "shortestpath" vector map 
> from "categorymap" and not from my original dataset "slc", how can I 
> specify to v.net.path to take into account values from "slc"?

You have to calculate costs in one column and then use afcolumn, 
abcolumn, ncolumn.

Radim

> Thanks for any help you can give me.  I really appreciate it.
> 
> Ryan T.
>