[GRASS-user] nan values by v.generalize

Daniel Bundala bundala at gmail.com
Sun Dec 16 16:23:53 EST 2007 

The patch is attached. Hope it works.

Daniel

On Dec 16, 2007 7:03 PM, Wolf Bergenheim <wolf+grass at bergenheim.net> wrote:
> I think that would be OK.
>
> If you send the patch to the list I'll commit it to trunk and the 6.3
> release branch.
>
> --Wolf
>
> On 16.12.2007 13:16, Daniel Bundala wrote:
>
> > Dylan,
> >
> > I was thinking about the problem last night and a solution I have come
> > up with is the following.
> >
> > As I mentioned in my previous post, a solution is to translate the
> > corresponding points little bit. I do not know how good this technique
> > is, but we can use it "approximate" the tangent at the point in
> > between. My reasoning is: Take two points p1, p2 which are L metres
> > apart. And we send p1 to p2 (or vice verse), i.e. L goes to 0 and take
> > the limit. Then we get (according to the calculation I do in
> > v.generalize) that the tangent is zero.
> >
> > I think that this behaviour is consistent with the other possible
> > situations and shapes of lines. Especially, it would be better if the
> > algorithm does something "reasonable" which imitates the situations if
> > the points are close to each other.
> >
> > If no-one is against this, I will add that one line to the code...
> >
> > Daniel
> >
> > On Dec 15, 2007 8:36 PM, Dylan Beaudette <dylan.beaudette at gmail.com> wrote:
> >> On Saturday 15 December 2007 05:38:44 am Daniel Bundala wrote:
> >>> Hello,
> >>>
> >>> I am not 100% certain as I did not test it, but I think that the
> >>> problem is that the very last line in myvect map contains 2 points at
> >>> the exactly same position (131.5, 67.5). Actually, you are so lucky to
> >>> get this (faulty?) behaviour:) because this occurs only if there is
> >>> exactly one point in between them. In your case, 2nd and 4th points
> >>> have the same position whereas 3rd is at a different position.
> >>>
> >>> Possible solutions are:
> >>> -Firstly, is your map correct? I mean, does it make a sense to you
> >>> that one of your lines is of this strange shape?
> >>> -If yes, then I believe that the behaviour of the algorithm is
> >>> undefined. Because Hermitian interpolation needs to have some "notion"
> >>> of a tangent at each point. And I really don't know what can be a good
> >>> choice of a tangent at points like your 3rd point on the last line.
> >>> -So you can either use different smoothing algorithm (Chaiken?) or
> >>> shuffle the second and fourth point little bit so that they do not
> >>> coincide. In other words, translate the second point to 131.5000001
> >>> 67.500001 and fourth point to 131.49999999 67.499999 say. In the later
> >>> case, I doubt that the output of v.generalize will be particularly
> >>> nice......
> >>>
> >>> Hope this helps,
> >>> Daniel
> >>
> >> Daniel / others:
> >>
> >> how about doing a first pass to check for points / segments where the
> >> requested interpolator is undefined ? That way an appropriate warning could
> >> be issued along with suggestions like you have presented.
> >>
> >> I suppose that a moving window on the vertices could accomplish this, checking
> >> for the conditions above.
> >>
> >> What do you think?
> >>
> >> Cheers,
> >>
> >> Dylan
> >>
> >>
> >>> On Dec 14, 2007 4:41 PM, Andre Hauptfleisch <ahaupt at gmail.com> wrote:
> >>>> I've attached the myvect and myvect_smooth files.
> >>>>
> >>>> Thanks for the help!!
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> On Dec 14, 2007 4:53 PM, Moritz Lennert <mlennert at club.worldonline.be >
> >>>>
> >>>> wrote:
> >>>>> On 14/12/07 15:37, Andre Hauptfleisch wrote:
> >>>>>> I'll try to upload the vector layer I used to an ftp site. What would
> >>>>>> the best output format be? DXF?
> >>>>> You can just use the output of v.out.ascii. If the file is not too
> >>>>> large, you can zip the output and send it to me directly.
> >>>>>
> >>>>> Moritz
> >>>>>
> >>>>>> On Dec 14, 2007 4:13 PM, Moritz Lennert <
> >>>>>> mlennert at club.worldonline.be
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> <mailto: mlennert at club.worldonline.be>> wrote:
> >>>>>>
> >>>>>>     On 14/12/07 14:48, Andre Hauptfleisch wrote:
> >>>>>>      > Good day guys,
> >>>>>>      >
> >>>>>>      > I came across a problem in the v.generalize module. I do the
> >>>>>>
> >>>>>>     following:
> >>>>>>      > v.generalize input=myvect at test output=myvect_smooth type=line
> >>>>>>      > method=hermite threshold=10
> >>>>>>      >
> >>>>>>      > I then do a v.out.svg and noticed the following line in the
> >>>>>>      > svg
> >>>> file:
> >>>>>>      > <path gg:cat="31" d="M 111.500000 -80.500000 l 8.734748
> >>>>>>      > 4.771559 9.907176 6.337565 nan nan nan nan nan nan nan nan nan
> >>>>>>      > nan" />
> >>>>>>      >
> >>>>>>      > Any idea how I can get rid of those nan's? They cause stuff
> >>>>>>      > such
> >>>> as
> >>>>
> >>>>>>      > v.to.rast to hang.
> >>>>>>
> >>>>>>     I cannot reproduce this with the speafish60 dataset:
> >>>>>>
> >>>>>>     v.out.svg input=roads at PERMANENT output=roads type=line
> >>>>>> precision=6 layer=1
> >>>>>>
> >>>>>>     and
> >>>>>>
> >>>>>>     v.generalize input=roads at PERMANENT output=roads_smooth type=line
> >>>>>>     method=hermite threshold=10 look_ahead=7 reduction=50 slide= 0.5
> >>>>>>     angle_thresh=3 degree_thresh=0 closeness_thresh=0
> >>>> betweeness_thresh=0
> >>>>
> >>>>>>     alpha=1.0 beta=1.0 iterations=1 layer=1
> >>>>>>
> >>>>>>     v.out.svg input=roads_smooth at user1 output=roads_smooth type=line
> >>>>>>     precision=6 layer=1
> >>>>>>
> >>>>>>     Both give me svg files without nan's.
> >>>>>>
> >>>>>>     Can you reproduce this with spearfish data ? Can you look at the
> >>>> line
> >>>>
> >>>>>>     with cat=31 in your grass vector (maybe in v.digit) and see if
> >>>>>> there
> >>>> is
> >>>>
> >>>>>>     anything abnormal about it ?
> >>>>>>
> >>>>>>     Moritz
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> --
> >>>>>> Groete,
> >>>>>> Andre Hauptfleisch
> >>>>>>
> >>>>>> M: 082 5722 469
> >>>>>> F: 086 687 1106
> >>>>>> E: ahaupt at gmail.com <mailto:ahaupt at gmail.com>
> >>>> --
> >>>> Groete,
> >>>> Andre Hauptfleisch
> >>>>
> >>>> M: 082 5722 469
> >>>> F: 086 687 1106
> >>>> E: ahaupt at gmail.com
> >>>> _______________________________________________
> >>>> grass-user mailing list
> >>>> grass-user at lists.osgeo.org
> >>>> http://lists.osgeo.org/mailman/listinfo/grass-user
> >>> _______________________________________________
> >>> grass-user mailing list
> >>> grass-user at lists.osgeo.org
> >>> http://lists.osgeo.org/mailman/listinfo/grass-user
> >>
> >>
> > _______________________________________________
> > grass-user mailing list
> > grass-user at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/grass-user
>
> --
>
> <:3 )---- Wolf Bergenheim ----( 8:>
>
>
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smoothing.diff
Type: application/octet-stream
Size: 745 bytes
Desc: not available
Url : http://lists.osgeo.org/pipermail/grass-user/attachments/20071216/193e41c7/smoothing-0001.obj

More information about the grass-user mailing list