gridding and horizons

The gridding and horizons module uses data files containing geologic horizons or surfaces (usually .geo, .gmf and other ctech formats containing surfaces) to model the surfaces bounding geologic layers that will provide the framework for three-dimensional geologic modeling and parameter estimation. Conversion of scattered points to surfaces uses kriging (default) or spline (previously in the spline_geology module), IDW or nearest neighbor algorithms.

gridding and horizons creates a 2D grid containing one or more elevations at each node. Each elevation represents a geologic surface at that point in space. The output of gridding and horizons is a data field that can be sent to several modules (e.g. 3d estimation, horizons to 3d, horizons_to_3d_structured, surfaces from horizons, etc.) 

Those modules which create volumetric models convert the quadrilateral elements into layers of hexahedral (8-node brick) elements. The output of gridding and horizons can also be sent to the surface from horizons(s) module(s) which allow visualization of the individual layers of quadrilateral elements (the surfaces) that comprise the surfaces.

gridding and horizons has the capability to produce layer surfaces within the convex hull of the data domain, within a rectilinear domain with equally spaced nodes, or within a rectilinear domain with specified cell sizes such as a finite-difference model grid. The finite-difference gridding capabilities allows the user to visually design a grid with variable spacing, and then krige the geologic layer elevations directly to the finite difference grid nodes. gridding and horizons also provides geologic surface definitions to the post_samples module to allow exploding of boreholes and samples by geologic layer.

Note: gridding and horizons has the ability to read .apdv, .aidv and .pgf file to create a single geologic layer model. This was not done as a preferred alternative to creating/representing your valid site geology. However, most sites have some ground surface topography variation. If 3d estimation is used without geology input, the resulting output will have flat top and bottom surfaces. The flat top surface may be below or above the actual ground surface at various locations. This can result in plume volumes that are inaccurate.

When a .apdv or .pgf is read by gridding and horizons the files are interpreted as geology as follows:

1)    If Top of boring elevations are provided in the file, these values are used to create the ground surface.

2)    If Top of boring elevations are not provide in the file, the elevations of the highest sample in each boring are used to create the ground surface.

3)    The bottom surface is created as a flat surface slightly below the lowest sample in the file. The elevation of the surface is computed by taking the lowest sample and subtracting 5% of the total z-extent of the samples.

When reading these files, you will get a single layer which goes to either the Top column (if it exists) otherwise, the top sample in each boring, and 5% below the lowest sample in the file (flat bottom). This allows you to create a convex hull around data without having geology info. It also provide a topographic top surfaces if your analyte (e.g. chemistry) or PGF file has Tops (grounds surface elevations). Also nice for doing indicator kriging (since a single, well-defined pgf can give you an entire indicator model now). Be aware that if Top is specified, but all values are exactly 0.0, the top sample elevation for each boring will be used.

Module Input Ports

• Filename [String / minor] Receives the filename from other modules.

Module Output Ports

• Geologic legend Information [Geology legend] Supplies the geologic material information for the legend module.
• Output Geologic Field [Field] Can be connected to the 3d estimation, 3D_Geology Map, and surface from horizons(s) modules.
• Filename [String / minor] Outputs a string containing the file name and path. This can be connected to other modules to share files.
• Status Information [String / minor] Outputs a string containing module parameters. This is useful for connection to write evs field to document the settings used to create a grid.
• Geology Export Output [Vistas Data / minor] Provides input to the export horizons to vistas and other modules which create raster output.
• Grid [Renderable / minor] Outputs the geometry of 2D grid.

Properties and Parameters

The Properties window is arranged in the following groups of parameters:

• Grid Settings: control the grid type, position and resolution
• Krig Settings: control the estimation methods
• Computational Settings: define computational surfaces included in the output. This allows a single surface file to define a layer specified by elevation or depth.