[GRASS-user] Snapping Points to Nodes along Lines

[Moritz Lennert]

On 01/10/08 04:28, Ryan R. Rosario wrote:
> Hmm. If I do 
> 
> v.net input=result_from_connect output=projected_points

The command you give here will call operation=nodes as this is the 
default (see man page).

> 
> I do get the point projected onto the line, but I also get points at each
> intersection as well as at the end of each street. 

Yes, this is the normal result fro the what the command you give above.

> Is there any way I can
> get just the projected points?

Sorry, I only now seem to really understand what you want to do.

There's no direct way of doing that, so you will have to take a detour. 
The easiest way I can think of like that is:

1) run v.distance with the output= option to create a map of connecting 
lines

then either

2a) on the result of 1) run v.net operation=nodes and then v.net 
operation=report to get cat values of the points (just have to figure 
out which ones are considered start and which end - I suppose that this 
will be uniform), then run v.extract on those category values to extract 
just these points which represent the projection

or

2b) on the result of 1): (you might have to use v.db.addtable on that to 
create a table first, can't remember) run v.db.addcol to add to columns 
of double precision 'X' and 'Y', then run v.to.db with option=start or 
option=end (again you have to figure out which it is) to upload the 
coordinates of the start/end points to the table linked to the result of 
1). Then you can use v.in.db to create a new vector map containing these 
points.

Tell us if any of these two solutions work for you.

Moritz