[GRASS-user] serious problem with "ROUND-OFF"

[achim]

Hi Hamish,

thanks for your suggestions. It is very useful to get ideas from a
different perspective!

I am sorry, that I have to write a 'but' again:

> > r.to.vect the area
..I have no areas to extract. I have a river network, for which I want
to subdivide some lines.
Because I have some thousands of lines, I always get some
start/end-nodes on these critical points on the border between two
raster-cells.

> > add cats to boundaries with v.category
> > v.type the boundary to line
> > v.extract the lines
> > v.buffer the lines to about the cell width
> > v.overlay op=not
Otherwise that would help!! (Even though v.buffer would take sooo... long)

Best regards,
Achim

> >
> > ?
> >
> >
> > Hamish
> >
> >
> >
> > --- On Wed, 30/9/09, achim <ak7 at jupiter.uni-freiburg.de> wrote:
> >
>> >> From: achim <ak7 at jupiter.uni-freiburg.de>
>> >> Subject: Re: [GRASS-user] serious problem with "ROUND-OFF"
>> >> To: "grass-user" <grass-user at lists.osgeo.org>
>> >> Received: Wednesday, 30 September, 2009, 4:37 AM
>> >> Dear grass users,
>> >>
>> >>
>> >> I think I know what is needed...
>> >>
>> >> to solve the problem (see below, mainly coming from
>> >> splitting lines on
>> >> edges between raster-cells), I will have to:
>> >> 1) identify the verts
>> >> 2) move these verts on the line (direction of the line) at
>> >> certain
>> >> distance (about half grid-size)
>> >>
>> >> That would solve the problem mainly, but I have no idea how
>> >> to deal with it.
>> >> Any help, suggestions or opinions are very welcome!
>> >>
>> >> Thanks in advance,
>> >> Achim
>> >>
>> >> achim schrieb:
>>> >>> Hi all,
>>> >>>
>>> >>> I have a problem, I really would like to solve,
>> >> because many problems
>>> >>> occur in my theses in further steps.
>>> >>>
>>> >>> What I do is:
>>> >>>
>>> >>> 1. I break lines at some lengths.
>>> >>> 2. I use both vector- and raster-data for analysis,
>> >> which is eg.
>>> >>> updating points with raster-values or converting lines
>> >> and points to raster.
>>> >>> The Problems are (due to rounding or
>> >> "non-snapping"?):
>>> >>> !Points from lines on the edge between two diagonal
>> >> cells (see pictures)!
>>> >>> These points do:
>>> >>> 1. not belong precisely to one cell (compared with the
>> >> line they come
>>> >>> from (see picture v.to.rast.png)
>>> >>> 2. These points sometimes don't lie on on the cells,
>> >> the line is
>>> >>> referred to (see picture break.png)
>>> >>>
>>> >>> Any hints are very welcomed!
>>> >>>
>>> >>> Thanks in advance,
>>> >>> Achim
>>> >>>
>>> >>>
>>> >>>
>> >>
------------------------------------------------------------------------
>>> >>>
>>> >>>
>> >>
------------------------------------------------------------------------
>>> >>>
>>> >>>
>> >>
------------------------------------------------------------------------
>>> >>> _______________________________________________
>>> >>> grass-user mailing list
>>> >>> grass-user at lists.osgeo.org
>>> >>> http://lists.osgeo.org/mailman/listinfo/grass-user
>> >> -----Inline Attachment Follows-----
>> >>
>> >> _______________________________________________
>> >> grass-user mailing list
>> >> grass-user at lists.osgeo.org
>> >> http://lists.osgeo.org/mailman/listinfo/grass-user
>> >>
> >
> >
> >