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

[Michael Barton]

On 11/16/07 5:48 AM, "Moritz Lennert" <mlennert at club.worldonline.be> wrote:

> 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.

Thanks very much for the clarification. This is far from clear in the docs.
Are the entries for each path (cat,start,path) to be separated by spaces or
a return in the text file?
 
1 start end 2 start end 3 start end...

OR

1 start end
2 start end
3 start end
...

> 
>> 
>> 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,...

Multiple entries of 3 separated by a comma or semicolon in a module option
(e.g., "startend=1 start end,2 start end,3 start end,...") would be no more
difficult to type and easier for non-unix types to understand than piping
the same info to the command (i.e., 1 start end 2 start end | v.net.path...)

Michael

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__________________________________________
Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton