[GRASS-dev] doc 'upgrade' request for v.net.path

[Moritz Lennert]

On 15/11/07 16:30, Michael Barton wrote:
> Eric,
> 
> Here's something to add to the rapidly growing list. I was helping one 
> of my students work with vector networking, something I don't do a lot 
> of. The shortest path module, v.net.path is actually pretty easy to work 
> with. But the docs are so confusing that it took us quite awhile to 
> figure out how to specify the start and end point. There seems to be a 
> fair amount of extraneous stuff in the example that is not necessary to 
> use the module--maybe because most of this help file dates from the 
> early days of GRASS 5.7. It would be nice if someone who knows these 
> modules well take a look at them. I'm also copying the student, Andrea, 
> in order to give her your email because she is interested in helping 
> develop documentation in Spanish and has colleagues who might be able to 
> help.
> 
> Here is a wish for someone else on the list...
> 
> Deciphering the docs for v.net.path, I figured out that the only ways to 
> specify start and end points  (AFAICT, but I could be missing something) 
> are 1) to pipe them into the command or 2) put them into a text file and 
> open the text file with the command. Both seem overkill, since all you 
> have to give the command is the following string:
> 
> "1 [startcat] [endcat]"
> 
> ...where [startcat] = the cat number of the starting node and [endcat]= 
> the cat number of the ending node. It is still unclear to me what the 
> "1" is for since it doesn't seem to apply to layer (i.e., the nodes in a 
> network are normally in layer 2).


1 is the id you wish to give to the resulting line. v.net.path 
automatically creates a category number, but it also creates an id 
column which contains this number.

This is linked to the fact that you are not limited to two points, i.e. 
two paths, but you can feed as many start and end points as you want to 
v.net.path.

> 
> It would seem a lot easier to simply have a "startend=" option built 
> into v.net.path that takes 2 cats separated by a comma.

This would then limit the use to one path, unless you actually allow 
entry of multiples of 3 in the form id,start,end,id,start,end,...

Moritz