[GRASS-user] How to query z coordinate in GRASS7 ? or intersection between 2 3D vector ?

[Le Jeune Yann]

Hi dear grasslist !

I haven't post on your list for a long time (10 years ?), but i usually use
the archive to find an answer, and it works most of the times.
Working in a archaelogical service (Nantes, France), we use GRASS to
produce raster models and "zoning" for archeological sensible surfaces
(provided online - in french - here :
http://atlas.patrimoines.culture.fr/atlas/trunk/index.php?ap_theme=DOM_2.01&ap_theme=DOMREG&ap_adm=REG_52&ap_bbox=-2.62;46.27;0.92;48.57).
I would like to thanks all the GRASS team and developers for their
works. It helps a lot to save and study archaeological sites here !!

We are now working on 3D data (LIDAR, lasergrammetry and photogrammetry) in
archaeological contexts. For that purpose i have done some test with GRASS
(6.4.2) and, recently with GRASS7 (src snapshot). Thanks to the great
advances in vector processing in GRASS7 (harder, better, faster, stronger
!) we can now import huge 3D pts datasets (like 72 millions of points).

We would like to automate (first of all, horizontal) slicing in 3D points
clouds for objects, buildings or excavations. First we tried to do some
query on Z using sql (v.to.db option=coor) it works for "light" models
(like 200000 pts) but is to slow or time/ressources/DB consuming on "heavy
models" (72 Millions pts). So, here comes my questions :

- is there a way to do a query (select/extract) on Z coordinate without DB
? something like : select all pts with a Z between 1.05 and 1.1
- is there a way to do a slice with 3D vectors ? Intersection of 2
different vector would be great ! (for example : between faces/mesh and a
plan) I haven't found/understand how to do that.

I have a look at lastools (recommended on a previous post in grasslist) but
it don't seems to do exactly what i want, even if las2iso do some good
work. Paraview could help, but as we want to automate and use in GIS
environment, it would be great if it works in GRASS7.

Thanks !!!

Yann
(GRASS on Linux mint debian/ 6.4.2 and 7 src snapshot)
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