[GRASS-user] Result of v.hull into solid 3D polygon with volume

Benjamin Ducke benducke at fastmail.fm
Fri Feb 16 01:21:30 PST 2018

Hi Vil,

at the time 3D support was added to v.hull, the new
3D vector API for GRASS had just been released, and
there was some uncertainty about the role of the
new geometry type "volume". Back then, there was
hardly any GRASS module that could do anything useful
with that type. Has that changed by now? If "volume"
is a usable type, then it should not be too difficult
to add a flag to produce a volume as output.

The function that would need to be modified is:

vector/v.hull/chull.c: void writeVertices(*Map)

In any case, in hindsight it looks weird now that
v.hull produces 3D faces plus a "kernel".

Maybe it would make more sense to output either
only 3D faces OR a volume plus a kernel?

In addition: For the next release, it would make
sense to rename this volume to v.hull.convex,
seeing that there is also v.hull.concave.



On 15/02/18 19:09, Vilem Ded wrote:
> Hi,
> I wonder if the 3D result of  "v.hull" function can be converted into
> object of type "volume"?
> Right now it is giving me just faces of the 3D polygon and 1 kernel.
> Which is according to specifications ("The 3D hull will be composed of
> triangular faces. ")
> Moreover I wanted to import this object into PostGIS as one 3D spatial
> polygon and make it solid (i need to compute volume and overlay with
> points), but of course it was imported as bunch of 3D polygons
> represinting those faces. And making 3D solid polygon (ST_MakeSolid?) in
> PostGIS is probably question for another mailing list.
> Thank you
> Vil
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Dr. Benjamin Ducke
Deutsches Archäologisches Institut (DAI)
Zentrale Berlin, IT-Referat
* Projekt "Stunde Null" *

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