[GRASS-user] kml topology... ?

[Nikos Alexandris]

On Thu, 2008-02-28 at 09:23 -0800, Dylan Beaudette wrote:
> On Thursday 28 February 2008, Nikos Alexandris wrote:
> > On Thu, 2008-02-28 at 09:15 -0800, Dylan Beaudette wrote:
> >
> > Thank you for your reply Dylan!
> >
> > > On Tuesday 26 February 2008, Nikos Alexandris wrote:
> > > > Continuing my small quest with kml files... and bombing you with simple
> > > > questions ;-p
> > > >
> > > > are kml files carrying topology information besides coordinates?
> > >
> > > I doubt it. As far as I know they are just "simple features".
> > >
> > > > I needed to manually correct a kml file which looked very bad after
> > > > importing in GRASS (with -c  otherwise it was not useful!)
> > >
> > > i am not surprised that a KML file resulted in a topologically broken
> > > file. These days everyone and their brother are creating KML via all
> > > sorts of methods-- most of which have little notion/concern for
> > > topological-correctness.
> >
> > +1
> >
> > > > Automatic cleaning is really not useful even after trying to feed with
> > > > logical thresholds the various tools.
> > >
> > > Try opening the file with v.digit and look for oddities.
> 
> Hi,
> 
> > Had to correct (almost) everything. Tha data are supposed to come from a
> > GPS measurement session.
> 
> I would think that the results from such as session be points or lines...

Probably. GPS measurement from a Forest Service office in Greece. I am
not saying it ironically, but not everybody knows how and, even worse,
takes the time to set-up a GPS session properly... and this could be the
case.
> 
> > All polygons were open after importing in GRASS. Yet there were
> > centroids inside this virtually closed boundaries. And the strange thing
> > is that one (call it) centroid was out of the virtual boundaries...
> 
> I wonder where the polygons came from -- could it be that one of the import 
> steps mistook the geometry in KML file as polygons? Line data that are 
> interpreted as polygons---especially in the presence of overlapping 
> features---would definitely cause some craziness.  

Fire, as known, was for Greece a Tragedy this summer. There is a private
initiative from somebody doing a great job: collecting burnt area's and
publishing under GPL in kml formats. It's a great job from all kinds of
aspects (political, social, etc). Of course this is not the place to
extend the discussion about this.

However,

I discovered that importing a kml file of my interest (finally) in GRASS
didn't show me what I expected to see.

> 
> > Don't know, maybe my mistake for this last statement about the centroid
> > falling out.
> >
> > Cheers!
> 
> Have the original data on hand?

One example http://tilaphos.blogspot.com/2008/01/blog-post_30.html 

The kml file I am talking about is (for which it is stated that it's
only a rough estimation of burned areas):
http://tilaphos.googlepages.com/Korinthia_estimate_2007.kmz

(there are lot's of kml's.. all of them referering to burned areas)

I am about to prepare a small step-by-step guide on how to import kml's
in GRASS. I got support from the man who run's the blog as well.

I would like to point out some basics about topology, shapefiles and kml
files. Of course I am not the Expert on all but a some remarks I could
provide to improve future GPS sessions.

If you are interested more I can play the translator.