[Freegis-list] change vector line direction

[Maciek Sieczka]

On Fri, 28 Apr 2006 12:23:50 +0200
Markus Neteler <neteler at itc.it> wrote:

> On Thu, Apr 27, 2006 at 10:15:38PM +0200, Maciek Sieczka wrote:
> > Hi!
> > 
> > I've been looking for a software which can change vector line
> > direction attribute. A thing that ArcInfo has been a long time able
> > to do...
> > 
> > Really, any hints, for any format and platform, please.
> > 
> > Thanks,
> 
> Maciek,
> 
> I guess that you are GRASS user :-)

You bet :D

<Great Markus Examples follow>

> But I am not sure why you need this. GRASS is supporting
> forward *and* backward direction.

I need to:

1. turn my lines of watercourses in the proper direction - the way the
water flows

2. transform stream's ending nodes to points (v.to.points, easy)

3. upload the DEM elevation under each stream node into datatable
(v.what.rast, dito)

4. calculate whether the cell under the ending stream node is lower than
the one under the starting node, as to DEM elevation (easy with 'along'
attribute we have from v.to.points)

5. if starting is lower than the ending one, lower DEM under the
starting one as needed

6. feed my watercouses and the modified DEM into CachmentSIM GIS; it
will enforce drainage direction on the DEM, based on watercourses
location and the difference in elevation of starting and ending
stream cell

http://www.toolkit.net.au/catchsim/index.htm?Overview/WatercourseInterp/WaterCFrame.htm~mainFrame
(they are talking about the case when the input is contour lines, but
feeding a ready-made DEM and eforcing drainage right over it is also
possible, and that's what I'm gonna do)

Weird, but will work. Only step one was obscure, now thanks to
Markus and strk there are chances.

Thanks.

Maciek

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