[GRASS5] Re: [caj78500@pop16.odn.ne.jp: Bugreport GRASS 5]

[Markus Neteler]

Hi David, hi all

[I switch to the devel list]

On Fri, Oct 27, 2000 at 03:02:26PM +0000, David D Gray wrote:
> Hi Markus
> 
> This seems to be a `snap' problem. I've seen the same thing myself.
> Occasional grid cells don't show correct topology when using v.mkgrid. I
> think it must be because of micro-misalignments during the build
> process. A very small snap coefficient has always fixed it. You can't
> call this a feature, so it is probably a bug. But it is very difficult
> to secure exact coincidence of points without using tolerance limits of
> some kind (impossible - if different platforms have different fp
> behaviour). So the answer is probably to create a default snap radius of
> a very small amount, say 10e-6 * <ground resolution> (what do you think
> of this scale in general mapping terms - could it be a problem?), in
> v.support, though it would still be possible to over-ride it with
> threshold=0.
..mhhh, difficult question. I always hesitate to have auto-correction
of data, but in this case it seems to be required. The question is
what is the smallest usable value for <factor> * <ground resolution>:
Would 10e-9 do as well?

How to other GIS packages fix such a problem (they will have it, too).

> At some point we need to thoroughly overhaul v.build. This is now the
> commonest source of problems. I don't think there's anything
> release-critical that can't be worked around - as here.

Other developers, what's your recommendation/experience?

Kind regards
 
 Markus

> Markus Neteler wrote:
> > 
> > Hi David,
> > 
> > may I bother you again with a vector problem? You
> > are the specialist... :-)
> > 
> > Hope you don't mind,
> > many thanks in advance
> > 
> >  Markus
> > 
> >   ------------------------------------------------------------------------
> > 
> > Subject: Bugreport GRASS 5
> > Date: Fri, 27 Oct 2000 04:13:38 +0100
> > From: caj78500 at pop16.odn.ne.jp ()
> > To: neteler at geog.uni-hannover.de
> > 
> > Below is the result of your feedback form.  It was submitted by
> >  (caj78500 at pop16.odn.ne.jp) on Friday, October 27, 2000 at 04:13:38
> > ---------------------------------------------------------------------------
> > 
> > subject: Bugreport GRASS 5
> > 
> > platform: Linux/Intel
> > 
> > vendor: RedHat
> > 
> > cputype: Intel (i486, i586, pentium ...)
> > 
> > grassversion: I compiled the sources myself
> > 
> > cvsyesno: no, I got a source code package from the server
> > 
> > source_version: 5beta8
> > 
> > module: v.mkgrid, v.support
> > 
> > bugreport: I am working with etopo5 sample dataset, and have a problem
> > in the follwing operation.
> > 
> > -----------------------------------------------------------
> > Mapset <TEST> in Location <etopo5>
> > GRASS 5.0beta8 > v.mkgrid map=aaa grid=1,1 coordinate=135,38 box=1,1 angle=0 type=const value=1
> > 
> >  Creating vector header...
> >  Creating vector grid...
> >  Writing out vector rows...
> >  Writing out vector columns...
> >  Finished
> > 
> > Mapset <TEST> in Location <etopo5>
> > GRASS 5.0beta8 > v.support option=build map=aaa
> > 
> >    V.SUPPORT:
> > 
> > Selected information from vector header
> >  Organization:  US Army Const. Eng. Rsch. Lab
> >  Map Name:
> >  Source Date:
> >  Orig. Scale:   0
> >  No snapping will be done
> > 
> >     Reading Vector file.
> >  100%
> >     Building areas
> >     Building islands
> >     Attaching labels
> > PNT_TO_AREA failed: (135.500000, 38.500000) (Category 1)
> >  Number of lines:   8
> >  Number of nodes:   10
> >  Number of areas:   0
> >  Number of isles:   0
> >  Number of atts :   0
> >  Number of unattached atts :   1
> >  Snapped lines  :   0
> > -----------------------------------------------------------
> > 
> > Please help me to solve this "PNT_TO_AREA failed" problem.
> > What does influence v.support. I want to add attributes to
> > the grids automatically without v.digit. Using this "PNT_TO_AREA
> > failed" map as the cutter file, v.cutter fails to extruct
> > the vector objects from the vector map.
> > 
> > Thanks in advance.
> > 
> > -- caj78500
> > 
> > compiler: gcc
> > 
> > name: caj78500
> > 
> > ---------------------------------------------------------------------------
> > 
> > REMOTE_HOST: ige.mi.mss.co.jp

-- 
Dipl.-Geogr. Markus Neteler *  University of Hannover
Institute of Physical Geography and Landscape Ecology
Schneiderberg 50 * D-30167 Hannover * Germany
Tel: ++49-(0)511-762-4494  Fax: -3984

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