[GRASS5] New dig 5.0 format with categories and z-coordinate

[David D Gray]

Markus Neteler wrote:
> 
> 
> Dear Radim and David,
> 
> many thanks for the long awaited proposal! I am shure that an
> updated vector format would increase the acceptance of GRASS.
> 
> If you allow, a question concerning the Z-coordinate support:
> Do you think of tilted vectors (maybe 2.5D vectors) or even
> of full 3D vectors to construct geometric volumes like houses
> or whatever? The latter would require a format which allows to
> stack vectors and have vertical vectors etc.
> 

The core format is a true 3d format as there is no assymetry between the
x- and y- coords and the new z-coord. But most modules work on the
presumption of a projected 2d space, so in the first instance most
immediate applications will be to work with projection+elevation eg. a
projected TIN model. Also it will now be easier to work directly from
vector data to obtain true point to point values such as slopes, aspect
etc (instead of having to interpolate from raster or sites data).

Then, though this would be extra to our immediate plans, a volume
handling capability could be added by creating combinations of AREA into
SURFACE and SURFACE into VOLUME (we'd also need an EDGE). Then modules
to deal with g3d <-> v3d just as we do with the 2d stuff at present. We
could probably just hack this in to the existing system, mostly to
v.build and the display/edit modules, but I don't think much else, apart
from the new modules.

`CAD' type support would require 1) layers 2) a format, maybe a vector
graphics format 3) some kind of support for composite maps (this would
be a good idea generally-does anyone know if it has ever been
discussed?) where a combination of vector/raster/CAD etc layers could be
treated as one map.

So that is a bigger job. Maybe we could complete the immediate task, and
possibly create volume support through the course of development of
GRASS 5.x. However to go much further, do we want to continue hacking
more stuff on to GRASS3 dig and GRASS4 Vect, or is it time to think
about a rewrite of the vector engine? There is a spec for a vector
engine dating back some years, that was originally intended for
`GRASS6', in the documents directory, though it appears the code base no
longer exists (?).

David

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