[GRASSLIST:913] Re: Planning swath bathymetry surveys

[David Finlayson]

I've simplified my script a bit based on Hamish's suggestions. But I
still can't figure out how to get the vector areas to equal the vector
boundaries. I have messed around with v.clean a bit, but haven't
stumbled on the solution yet. Here is an update to the script and
another picture of what I am writing about:

http://pages.google.com/edit/david.p.finlayson/swathwidth

For my problem, buffering the nodes with circles means that the buffer
is working both normal to my line (which is what I want) but also
parallel to my line which is not ok for my application. Swath beams
don't spread out in a circle, they are thin rectangles. So, the
planning tool I am working on will overestimate the swath coverage
when the survey crosses from deep to shallow water (or vis-a-vis).


On 4/26/06, Maciek Sieczka <werchowyna at epf.pl> wrote:
> On Wed, 26 Apr 2006 15:23:39 +1200
> Hamish <hamish_nospam at yahoo.com> wrote:
>
> > > > 1) "It appears that v.buffer buffers the nodes on the line
> > > > segments rather than drawing parallel lines at the appropriate
> > > > distance from the centerline."
> > > >
> > > > I don't think that is right, if the input feature is a line.
> > >
> > > I guess statement 1) is somewhat right. See the attached screendump.
> > > Red is the input lines, black is the output of the command:
> > >
> > > v.buffer input=x_extr output=buffer type=boundary layer=1 buffer=100
> > > scale=1.0 tolerance=0.01 debug=buffer
> >
> >
> > I don't see the problem? Sure as part of the processing it buffers
> > about nodes, but after a disolve common boundaries cleaning step the
> > buffer looks correct between nodes as well? (see ski jump mid-right
> > side of your image)
>
> Why does it buffer around nodes anyway while we want it to buffer
> around lines (only)?
>
> Maciek
>
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>


--
David Finlayson