[GRASSLIST:958] Re: GRASS and vector lines: how can I change the direction of digitized lines?

[Otto Dassau]

Am Freitag, 28. April 2006 13:35 schrieb wqual:
> Hi GRASS list,
> I have two shapefiles which represent the average traffic load for some
> streets in Munich. The traffic is divided into "incoming" and "outgoing"
> traffic.
> What I would like to do: display this map in my mapserver application
> (using ttf-arrow symbols).
> However, mistakes were made during digitizing, thus the direction of the
> lines is wrong (looks like this
>
> ->------------>----------->
> ->------------>----------->
>
> and should be something like
>
> <--------<------------<-------
>
> >--------->------------>-------
>
> ).
> Therefore my question(s):
> a) is it possible to display these directions within GRASS (I tried to do
> this in ArcView before)

Hi Wolfgang,

the parameter in d.vect is display=dir

e.g.: d.vect roads display=dir,shape

> b) how can I change the direction of the lines in GRASS?

as far as I know you can't, because you define the direction when you digitize 
a line from node a ---->----- node b. But you can use columns in the 
appendant attribute table to assign different values for each direction (e.g. 
speed). 

see ->  g.manual v.net.path
...
afcolumn   Arc forward/both direction(s) cost column
abcolumn   Arc backward direction cost column

regards,
  Otto


> I would be most grateful for some comments on this issue.
>
> Best regards,
>
> Wolfgang