[GRASS-user] TIN and B/T correction in grass...
luca.penasa at email.it
Sun Nov 2 04:07:54 EST 2008
Hamish, thank you for your really exhaustive answer!
The second question was right for me...
> Do you have a TIN you would like to fix in GRASS? (original or rasterized?)
> Or you are wondering how GRASS deals with the bad side effects of TINs?
> To answer the first: each triangle confluence/vertex is a x,y,z data point.
> Together these describe all the available actual data in the model, the
> rest of the TIN is linear interpolation with some simple rules.
> What you need to do in GRASS is load or convert the TIN into its
> fundamental x,y,z data points, then use one of GRASS's more sophisticated
> surface generation modules to create a new surface. i.e. use v.surf.rst
> to generate a more realistic DEM with peaks and valleys than the simple
> TIN input describes.
> To answer the second: GRASS doesn't really "do" TINs, for (AFAICT) the
> simple reason that it doesn't have to resort to that. It has a very good
> and mature raster engine with much better surface generation tools. IMHO
> TIN is a hold-over technique for faux-raster surfaces from other GISs
> which have been historically strong with vectors but weak with raster
> data. (I would not count IDRISI among those, I speak more of Arc/Info,
> but...) You can search the mailing list archives for my previous diatribes
> on the subject. Of course all are free to work with whatever tools they
> prefer, there is a little about GRASS+TINs here:
> Unfortunately AFAICT mediawiki's search engine does not consider three
> letter words so it is hard to guess if there is any more content. (if not
> there will be in the mailing list archives)
> So my advice is to spend some time with v.surf.* and r.surf.* (including
> r.surf.nnbathy from wiki addons) and enjoy the things that GRASS does well.
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