[Gdal-dev] Breaking long lines/boundaries with OGR function?

[Markus Neteler]

Ari,

of course the pure import is fast, but the reconstruction
of topology takes time. Our idea is to deliver the data
in a way more suitable to fast topology reconstruction.
It's all about topology - I guess that your renderer
doesn't built it.

Hope this clarifies the idea (I'm no topology expert...),

 Markus


On Mon, Jun 26, 2006 at 10:53:24AM +0300, Ari Jolma wrote:
> Markus,
> 
> I'm not sure why the import should be effected by the spatial extents etc. In my
> code I "import" data from OGR each time I render it and there's no big overhead
> because of that. The code is also extremely simple. What would you consider
> "complicated"? I've for example looked at ghssh coastline data and they render
> reasonably fast.
> 
> Of course I don't know much about the way GRASS stored vector data or about the
> import tool :-)
> 
> Ari
> 
> On Mon, 26 Jun 2006 09:11:35 +0200 Markus Neteler <neteler at itc.it> wrote:
> 
> > Hi,
> > 
> > the following issue came up in GRASS:
> > v.in.ogr, the OGR based import tool, may take a long time if
> > the data contains long complicated polylines.
> > 
> > >From TODO
> > http://freegis.org/cgi-bin/viewcvs.cgi/grass6/doc/vector/TODO
> > > ============================
> > > v.in.ogr
> > > --------
> > > It would be useful to split long boundaries to smaller
> > > pieces. Otherwise cleaning process can become very slow because
> > > bounding box of long boundaries can overlap large part of the map
> > (for
> > > example outline around all areas) and cleaning process is checking
> > > intersection with all boundaries falling in the bounding box.
> > > ============================
> > 
> > Since I don't know OGR well enough, is there any function 
> > we could make use of to achieve splitting of long lines before
> > handing data over to (topological) GRASS?
> > 
> > I found 
> > http://ogr.maptools.org/drv_dgn.html
> > "Polygons and line strings with too many vertices will be split into
> >  a group of elmements prefixed with a Complex Shape Header or Complex
> >  Chain Header element as appropriate."
> > 
> > Something seems to be there (or nearby).
> > 
> > thanks for a hint
> > 
> >  Markus
> > _______________________________________________
> > Gdal-dev mailing list
> > Gdal-dev at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/gdal-dev
> > 
> 
> -- 
> Prof. Ari Jolma
> Kartografia ja Geoinformatiikka / Cartography and Geoinformatics
> Teknillinen Korkeakoulu / Helsinki University of Technology
> POBox 1200, 02015 TKK, Finland
> Email: ari.jolma at tkk.fi URL: http://www.tkk.fi/~jolma

-- 
Markus Neteler  <neteler itc it>  http://mpa.itc.it/markus/
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18        -       38050 Povo (Trento), Italy