[GRASS-user] 3D geological modelling

[paallen at attglobal.net]

Otavio,

I am mineral exploration geochemist/geologist. 
Grass has really good raster capablities and that
is what I mainly use.  For my geochemistry I use
grass for gridding my surface soil and rock data
and for the stream  sediment data I use the
r.watershed routine to create catchement polygons
(IF I have a "good" dem and the SRTM90m is not
always good enough!).  I often generate
topographic dem's from goverment contour maps or
use differential-GPS data.

You can create some tins in grass but it is a bit
of a pain and they cannot enclose a 3d-volumn. 
And now for the real geology-grass problem.  Grass
is only 2.5D.  Thus you can have a polygon with
z-elevations but one node cannot directly overlie
another node.  Grass has topology.  Thus it is a
bit of a problem with modeling geology.  At least
the last time I tried it. 

As far as drill holes & sections.  I always have
my geochem in an MS Access or Postgresql database.
 To create cross sections I cheat in 2D.  I create
the nodes of profile using distance from a
starting point in a new mapset in XY space.  My
data is all in UTM or Lat/Long.  I have a function
in Access & Postgresql that will take those UTM
coordinates along with the starting point and a
rotation from north and calculate an xyz that can
 be plotted on the cross-section.  So it is not
3-d  exactly.  

For drill hole (bore hole) data I do the same. I
have just completed my minimum-curvature algorithm
in MS-Access to calculate down-hole coordinates
for curved holes (ie hole with down-hole surveys,
distances, azimuths, inclinations).  With these
coordinates for the from and to measurements for
the geochemistry or geological observations I can
then easily create 3D or 2D line segments.  I
still need to write the minimum-curvature
algorithm for Postgresql.  

Feel free to contact me directly if you have any
more questions and good luck with grass.

Phillip J. Allen
Consulting Geochemist
Lakewood Colorado USA
paallen at attglobal.net



Hi

This is my first message to this discussion list.
I am interested in contact anyone applying Grass
to geological mapping,
integrating geology to geophysiscs and
geochemistry along drill holes and
surface geological stations to build 3D geological
models and geologic
sections.

Thank you

Otavio Licht

********************************
Otavio Augusto Boni Licht
Geologist, MSc, Dr
Minerais do Paraná S.A. - MINEROPAR
Máximo João Kopp St., 274 - Block 3, floor M
Santa Cândida
82.630-900 - Curitiba, State of Paraná, Brazil
Phone 55 41 3351-6923
Fax  55 41 3351-6950
otavio at pr.gov.br  or  olicht at yahoo.com.br