[GRASS-user] r3.in.xyz

[Francois Chartier]

Hi Moritz,

The idea is a bit novel.  I am working with over 20000 Boreholes (BH) with
soil information (silt, sand, gravel, Tills, and everything in between
etc.).  These are not distinct geological contacts with recognizable
stratigraphies that can be correlated, ex: this top of gravel corresponds
to this top of gravel in this BH etc.  The model domain is approximately 40
km by 40 km and extends from ground surface (DEM) to top of bedrock
(surface from geological survey), and thickness varies from approx. 15 m to
100 m.
As it would take years to correlate all the soil contact elevations, I am
approaching the problem from a different angle.  The dataset consists of
XYZ and Property (top of soil deposit) at each borehole location (XY).
Along the vertical axis of the borehole, there are multiple top of soil
deposits overlying on top of each other depending on the depth of the BH
and location.
In between each top of soil there are no data points in the database,
however, in the real world there is a soil property.  Therefore if i am
interpolating only the top of soil data, the interpolation method will do a
gradual change between the top (n) of that soil deposit and its bottom
which is also the top of the next underlying soil deposit (n-1).
In order to avoid this, I would like to ensure that the 'weight' of that
soil deposit thickness in the interpolation is considered. Whether the
interpolation modules in Grass GIS can (first option) do this interpolation
by considering that the property extends to the next underlying deposit, or
(second option) if i need to interpolate each elevation slice horizontally
in individual 2D raster and then combine them into a 3D raster.
If it is the second option, then i need to generate property data points
between tops and bottom contacts of each soil layer, then export each layer
per elevation and generate a 2D raster for each elevation. there might be
another way to tell grass to interpolate the data from the database only at
a give elevation slice.
Let me know if this is unclear and if it is I will make a cross section of
what I am trying to do.

Thanks for your time.
Francois

Le lun. 9 juil. 2018 à 10:04, Moritz Lennert <mlennert at club.worldonline.be>
a écrit :

> François,
>
> First of all, I meant r.to.rast3elev [1], not r.to.rast3. Sorry for the
> mixup.
>
> On 09/07/18 15:17, Francois Chartier wrote:
> > Thanks moritz.  I will try this. I have about 300 m of elevation to
> > interpolate so i might group by thickness bands of 2 metres etc.
> > Is there a way i can make a batch mode where i prep all the xy p by
> > elevation and then interpolate automatically onw after another all
> slices?
>
> I'm not sure what you mean by grouping by thickness bands.
>
> IIUC your data, you have a series of boreholes. For a given geological
> layer you have its top elevation at each borehole where this layer is
> encountered. Just interpolate these top elevations for each geological
> layer. This gives you an elevation map per geological layer.
>
> Then you can use r.to.rast3elev to create a 3D map.
>
> One issue I've observed in my (limited) experience with this module is
> the need to define relevant vertical region values (resolution and top
> and bottom limits). If the resolution is larger than the actual layer
> thickness, the result will obviously not be satisfying.
>
>
> Moritz
>
> [1] https://grass.osgeo.org/grass74/manuals/r.to.rast3elev.html
>
>
> >
> > On Mon, Jul 9, 2018, 03:01 Moritz Lennert, <mlennert at club.worldonline.be
> > <mailto:mlennert at club.worldonline.be>> wrote:
> >
> >     Le Sun, 1 Jul 2018 13:27:03 -0400,
> >     Francois Chartier <fra.chartier at gmail.com
> >     <mailto:fra.chartier at gmail.com>> a écrit :
> >
> >      > Hi,
> >      >
> >      > I am reposting the initial question:
> >      >
> >      > “I am working with a data set that consists of borehole logs with
> a
> >      > Top of a layer (layer 1) and the top of the underlying layer
> (layer
> >      > 2) (which is also the bottom of the overlying layer 1).
> Everything
> >      > in between the elevation of top of layer 1 and top of layer 2
> >      > correspond to a Layer 1 property.
> >      >
> >      > The thickness of Layer 1 varies and this layer may not exist
> >      > everywhere (pinches out).  Above the Layer the property is
> different;
> >      > in other words the property only starts below the Top of layer 1
> >      > until the underlying Top of the next layer. Not sure of the
> >      > capabilities of the interpolation in Grass and working with a very
> >      > large data set (i cannot link every top of layers together), my
> first
> >      > approach was to create a each Layer property for every elevation
> >      > slice along each Borehole axis, interpolating soil properties at
> >      > every elevation between Boreholes.
> >      >
> >      > The key question is can v.vol.rst (changed this from r3.in.xyz
> >     <http://r3.in.xyz>)
> >      > interpolate in 3D without a Property at every elevation slice,
> >      > • while respecting the condition that above the Top of the layer
> 2,
> >      > the property corresponds to the Overlying top layer 1, and
> >      > • that the property is continuous until the next underlying layer
> 3 -
> >      > can someone confirm this? To provide a bit of background, borehole
> >      > data bases, identify the top of layer as encountered when drilling
> >      > downwards, and provide the elevation of the next layer (pick); in
> >      > between the soil property is the same, however there is no data
> >      > points.  When interpolating, while there is no data point in
> between
> >      > the two geological picks, the property should still have weight in
> >      > the interpolation process.”
> >      >
> >
> >     v.vol.rst is a tool to interpolate a continuous value into a 3D
> space.
> >     So, I do not think that it is the tool you are looking for.
> >
> >     As already mentioned before:
> >
> >      > You probably want to use something like r.to.rast3. This would
> mean
> >      > interpolating each layer separately into 2D elevation maps and
> then
> >      > assemble them into 3D using r.to.rast3.
> >
> >     Have you tried this approach ?
> >
> >     Moritz
> >
>
>
>
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