Hi vector gurus,
find attached a vector bug which seems to need our attention.
Maybe it's an v.spag issue?
Thanks,
Markus
Hi everybody,
in fact I read only after submitting bug that v.spag detects
line crossings, but... if I use v.spag over a vector file
containing only two lines crossing I end up with a new vector
file with lots of lines and nodes (much more than 4 lines and
5 nodes that I expected). I was still using grass5beta8, if
that bug has already been corrected, I apologize... I'm
downloading beta11, tomorrow I will made another try.
Bye
Andrea
Markus Neteler wrote:
Hi vector gurus,
find attached a vector bug which seems to need our attention.
Maybe it's an v.spag issue?Thanks,
Markus
------------------------------------------------------------------------
Subject: [GRASS-bugs] vector files: topology rules broken
Date: Thu, 15 Feb 2001 15:36:43 GMT
From: aaime@libero.it ()
Reply-To: grass-bugs@geog.uni-hannover.de
To: grass-bugs@geog.uni-hannover.de, grass-bugs@intevation.deBelow is the result of your feedback form. It was submitted by
(aaime@libero.it) on Thursday, February 15, 2001 at 15:36:43
---------------------------------------------------------------------------subject: vector files: topology rules broken
area: grass5beta11
platform: Linux/Intel
vendor: RedHat
cputype: Intel (i486, i586, pentium ...)
xwindows: Xfree 4.0.1
windowsmanager: KDE 2.x
tcltkver: -- select --
grassserver: Hannover site
grassversion: Linux/Intel binaries
cvsyesno: -- select --
compiler: -- select --
bugreport: Documentation (GRASS programmer manual, "Vector Maps" claims that vector files are made of nonintersecting curves, and a "Topology
rule" says that arcs should not cross each other. That's a standard
planar enforcement rule but... it's not enforced! I have digited
a file with 2 crossing lines, run v.support and it's still saying
"2 lines, 4 nodes". v.digit displays only four nodes. So, GRASS
does not split lines at crossing, and it doesn't create a node in
the crossing, nor it refuses to accept that bogus file.name: Andrea Aime
---------------------------------------------------------------------------
REMOTE_HOST: monet7-176.comune.modena.it
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Andrea Aime wrote:
Hi everybody,
in fact I read only after submitting bug that v.spag detects
line crossings, but... if I use v.spag over a vector file
containing only two lines crossing I end up with a new vector
file with lots of lines and nodes (much more than 4 lines and
5 nodes that I expected). I was still using grass5beta8, if
that bug has already been corrected, I apologize... I'm
downloading beta11, tomorrow I will made another try.
Bye
Andrea
Hi Andrea
I have noted before that v.spag likes the lines to cross in a
well-behaved manner. If lines run over one another, they are not split
or are not processed correctly, or the module bombs out. ie, if you
have:
X------------X------------------------X
X-------------------------------------X
where the lines are supposed to be co-incident, you get:
X--X-X---X-X
and so on, or other errors.
I suspect that these problems come mostly from importing
double-digitised data, but it is certainly a problem if you are getting
duplicate lines from manual digitising.
I've sometimes found it helps a bit to run v.spag -i first (to do just
an identical lines check) then run the full check (without the -i
option). But v.spag -i cannot clean the example above, because tho'
these lines are co-incident, they are not identical. (Also this would
have to be re-run on the original)
We are planning for the future of vector processing that vector data
will be loaded up to a network structure before any kind of processing
is done. That will enforce a guarentee that all lines will be single,
and not run over each other (v.in.shape already uses such a structure).
Regards
David
PS. I've just checked v.spag on a `well-behaved' spaghetti map. It
splits OK, but doesn't label the newly created segments automatically. I
think we need some idea of a composite line to be built in dig_plus, a
bit like areas are composed from area edges and a point locator, but for
linear features..?
Markus Neteler wrote:
>
> Hi vector gurus,
>
> find attached a vector bug which seems to need our attention.
> Maybe it's an v.spag issue?
>
> Thanks,
>
> Markus
>
> ------------------------------------------------------------------------
>
> Subject: [GRASS-bugs] vector files: topology rules broken
> Date: Thu, 15 Feb 2001 15:36:43 GMT
> From: aaime@libero.it ()
> Reply-To: grass-bugs@geog.uni-hannover.de
> To: grass-bugs@geog.uni-hannover.de, grass-bugs@intevation.de
>
> Below is the result of your feedback form. It was submitted by
> (aaime@libero.it) on Thursday, February 15, 2001 at 15:36:43
> ---------------------------------------------------------------------------
>
> subject: vector files: topology rules broken
>
> area: grass5beta11
>
> platform: Linux/Intel
>
> vendor: RedHat
>
> cputype: Intel (i486, i586, pentium ...)
>
> xwindows: Xfree 4.0.1
>
> windowsmanager: KDE 2.x
>
> tcltkver: -- select --
>
> grassserver: Hannover site
>
> grassversion: Linux/Intel binaries
>
> cvsyesno: -- select --
>
> compiler: -- select --
>
> bugreport: Documentation (GRASS programmer manual, "Vector Maps" claims that vector files are made of nonintersecting curves, and a "Topology
> rule" says that arcs should not cross each other. That's a standard
> planar enforcement rule but... it's not enforced! I have digited
> a file with 2 crossing lines, run v.support and it's still saying
> "2 lines, 4 nodes". v.digit displays only four nodes. So, GRASS
> does not split lines at crossing, and it doesn't create a node in
> the crossing, nor it refuses to accept that bogus file.
>
> name: Andrea Aime
>
> ---------------------------------------------------------------------------
>
> REMOTE_HOST: monet7-176.comune.modena.it
>
> ----------------------------------------
> If you want to unsubscribe from grass-bugs
> mailing list write to:
> minordomo@geog.uni-hannover.de with
> subject 'unsubscribe grass-bugs'----------------------------------------
If you want to unsubscribe from GRASS Development Team mailing list write to:
minordomo@geog.uni-hannover.de with
subject 'unsubscribe grass5'
----------------------------------------
If you want to unsubscribe from GRASS Development Team mailing list write to:
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subject 'unsubscribe grass5'