[GRASSLIST:956] GRASS and vector lines: how can I change the direction of digitized lines?

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

I would be most grateful for some comments on this issue.

Best regards,

Wolfgang

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

Wolfgang,

I have just asked the same question on freegis list. There was some
good help! If you find any other solutions, please drop a line.

http://intevation.de/pipermail/freegis-list/2006-April/002839.html

Maciek

P.S.

I know in ArcInfo 8 you can change vector line direction, manually,
using a "v.digit - like" interface. I've used it to modifie water flow
direction along streams for TOPOGRID(ANUDEM) once.

I wish v.digit or QGIS grass digit could turn lines to.

Maciek

--------------------
W polskim Internecie s? setki milion?w stron. My przekazujemy Tobie tylko najlepsze z nich!
http://katalog.panoramainternetu.pl/

Good Morning Otto, hi list.
thank you very much for this hint. BTW, I found out that the mapserver needs a
special option specified to display the direction correctly (see [1] for
details]: GAP must be set to something negative.

Best regards,

Wolfgang

[1]
http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0310/msg00441.html

---8<----------------------------------------------------------------
Am Freitag 28 April 2006 pH:00:14 nachmittags/abends schrieb 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