[GRASS-user] Searching Docs about 3D geological modelisation

GRASS GRASS user
1

Well, you are in luck and trouble at the same time.
Out of all GIS I know, GRASS is the only one that's
competent at handling 3D, volumetric rasters (aka
voxels, which is really what you want for
stratigraphic models). On the other hand, efficient
voxel modelling from sparse 3D data, such as well logs
and transects remains really challenging.

The problem with well logs is also that often the data
is of a "qualitative" nature, indicating the presence
and absence of types of material. There is no interpolation
algorithm in GRASS currently which can handle that sort
of data well.

For visualization, you can export the voxel data to VTK format
and use ParaView or VisIt, which are both superbly
powerful.

I have attached two screenshots of models that I once
produced from log data. One has been interpolated with
GRASS' 3D splines algorithm (which was a bit cheating,
really), the other is some sort of 3D IDW interpolation
done directly in VisIt.
I don't think they turned out too great.

But, hey: it's still more realistic than drawing on a piece
of paper and playing the old "connect the logs with
lines" game...

Ben

MORREALE Jean Roc wrote:

Hello Grasslist,

I'm searching for papers, books or usecases covering the use of GRASS in
geology, mainly on the stratigraphic representations (well log,
schematic block diagram) and geomorphological (erosion, georelief
reconstruction) aspects.

This is an area I've not practiced so far so I would be interested to
know how people here deal with it in Grass (especially their rules for
building a 3d model from logs and exploiting it correctly but also any
kind of spicy stuff you can obtain from it).

Thre is some related papers I've already find on these subjects :

HydroGIS 96: Application of Geographic Information Systems in Hydrology
and Water Resources Management (Proceedings of the Vienna Conference,
April 1996). IAHS Publ. no. 235, 1996.

Spatial Geologic Hazard Analysis in Practice, J. David Rogers, 2004

Three-dimensional Geological Modeling by FOSS GRASS GIS, Atsushi
Kajiyama et al., 2004

Volume modeling of soils using GRASS GIS 3D-Tools, Markus Neteler, 2001

Regards,
MORREALE Jean Roc
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Benjamin Ducke
Geospatial Consultant

Oxford Archaeology Digital
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OX2 0ES
Oxford, U.K.

Tel: +44 (0)1865 263 800 (switchboard)
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(attachments)

idw-3d-model.png
fence-diagram-rst.png

2

On Thu, 7 Jan 2010, Benjamin Ducke wrote:

The problem with well logs is also that often the data is of a
"qualitative" nature, indicating the presence and absence of types of
material. There is no interpolation algorithm in GRASS currently which can
handle that sort of data well.

   So what is needed is a political algorithm. :slight_smile:

   Kidding aside, I suspect that a fuzzy interpolation algorithm would solve
the problem.

Rich

3

Thanks for the answers,

Having used it a little with archaeological structures it was no wonder that the first software I thought about was grass, but the main difference is, as you pointed out, that in this case I do not have a well defined volume.

I was thinking about using r3.in.ascii and then r.to.rast3 but it doesn't seems to be the right thing to do on a large scale (150km²) due to potential multiple top/bottom crossing of the generated layers.

Your screenshots are exactly the kind of data visualization I'm seeking to obtain.

Jean Roc

Le 08/01/2010 00:34, Benjamin Ducke a écrit :

Well, you are in luck and trouble at the same time. Out of all GIS I
know, GRASS is the only one that's competent at handling 3D,
volumetric rasters (aka voxels, which is really what you want for
stratigraphic models). On the other hand, efficient voxel modelling
from sparse 3D data, such as well logs and transects remains really
challenging.

>
> The problem with well logs is also that often the data is of a
> "qualitative" nature, indicating the presence and absence of types of
> material. There is no interpolation algorithm in GRASS currently
> which can handle that sort of data well.
>

I have attached two screenshots of models that I once produced from
log data. One has been interpolated with GRASS' 3D splines algorithm
(which was a bit cheating, really), the other is some sort of 3D IDW
interpolation done directly in VisIt. I don't think they turned out
too great.

>

But, hey: it's still more realistic than drawing on a piece of paper
and playing the old "connect the logs with lines" game...

You missed the use of Illustrator

Ben

MORREALE Jean Roc wrote:

Hello Grasslist,

I'm searching for papers, books or usecases covering the use of
GRASS in geology, mainly on the stratigraphic representations (well
log, schematic block diagram) and geomorphological (erosion,
georelief reconstruction) aspects.

This is an area I've not practiced so far so I would be interested
to know how people here deal with it in Grass (especially their
rules for building a 3d model from logs and exploiting it correctly
but also any kind of spicy stuff you can obtain from it).

Thre is some related papers I've already find on these subjects :

HydroGIS 96: Application of Geographic Information Systems in
Hydrology and Water Resources Management (Proceedings of the Vienna
Conference, April 1996). IAHS Publ. no. 235, 1996.

Spatial Geologic Hazard Analysis in Practice, J. David Rogers,
2004

Three-dimensional Geological Modeling by FOSS GRASS GIS, Atsushi
Kajiyama et al., 2004

Volume modeling of soils using GRASS GIS 3D-Tools, Markus Neteler,
2001

Regards, MORREALE Jean Roc
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