In a previous post,
we showed an example of how a topography could be modeled in 3DEC using
the ‘octree’ approach. First, a geometry surface is imported (e.g., a
dxf file) and a small number of blocks are created. Then, each block
that is touching the geometry surface is split into eight smaller
blocks. This continues until there is a satisfactory representation of
the surface geometry (see the figure below). The downside of this
approach is that the ‘stair-step’ mesh is fairly unattractive and
sometimes there is spurious failure at the sharp corners of these cubic
blocks. It also can lead to a lot of blocks (26,000 in the plot below).
A much better representation of the surface can be obtained using
Kubrix Geo. This software can generate a tetrahedral mesh to match
exactly to a desired topography (or any other geometry). The advantage
of Kubrix is that it can mesh intersecting surfaces, tunnels, geological
units, and even non-planar faults.
However, if you are interested only in representing a topography, or
perhaps a few non-intersecting horizons, there is another way. You can
import the geometry surface and then extrude each polygon that makes up
the surface using the POLY PRISM command in 3DEC. This requires a bit of
FISH (see link below), but the result is worth it. You can see in the
plot below that not only is the surface much smoother than the octree
surface, there also are significantly fewer blocks (3,300 in the plot
below). The downside is that some of these blocks may have problematic
geometries (e.g., high aspect ratios). This can be mitigated somewhat by
ensuring that you have a good mesh and by making some horizontal cuts.
Identifying and dealing with bad blocks will covered in a future post.
Revised - July 02, 2016. Set atol to 0.1 to prevent geometry errors.
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