Spline_Geology is an alternative to Krig_3D_Geology that uses the thin plate spline method for estimating surfaces from scattered data points. We have found that this method creates wonderfully smooth surfaces that honor your data. It is reasonably fast and is often preferable to kriging with small datasets (less than 50 points) but tends to slow down rapidly with large datasets. The nature of the solver makes it impossible to predict the time to completion. If running with datasets with more than 50 samples, be prepared for long run times with no progress feedback.
Module Input Ports
Spline_Geology has an Orange-Blue-Orange input port that can receive the geology file name.
Module Output Ports
Spline_Geology has six output ports.
1) Read_geo_data_file (Orange-Blue-Orange) : Supplies the geology file name.
2) Vistas Group (blue-magenta-blue-magenta) : Provides input to the Geology_to_Vistas module.
3) (brown-grey-green/brown-yellow/brown) : Provides geologic material information for the Legend module.
4) status_out(blue/green) : Outputs a string containing status updates while the module is running.
5) output0 (blue-white-green) : The primary output field. The primary output field port can be connected to the Krig_3D, 3D_Geology Map, and Geologic Surface modules.
6) Grid_out (red) : Outputs a renderable geometry of a finite difference grid.
General Module Function
Spline_Geology has fewer options than Krig_3D_Geology. It always uses all of your sample locations and therefore does not have parameters to adjust it's interpolation process.
The Gridding Options subpanel of Spline_Geology is shown above.
Although it is at the bottom of the subpanel, the first option that should be set by the user is Grid Type, as this will determine the nature of the domain that will be kriged. The Rectilinear option is used when the user wishes to produce a model that contains estimated values everywhere inside a user specified rectangular domain. The Convex Hull Boundary Option is used when the user wishes to produce a model that can have an irregular boundary that is defined by the distribution of measured data points. The Convex Hull of a data set can be thought of as the domain that would be outlined by stretching a rubber band around the external data points in the data set. The Convex Hull boundary option effectively minimizes the extrapolation of parameters within the model to that area which is enclosed by the measured data points. The Finite Difference domain allows the user to krige the elevations of the geologic layers directly to the finite difference grid node locations that were setup in the control panel of Krig_3D_Geology. Note that the finite difference grid must be designed and displayed before the user selects a .geo file and clicks the Accept all Current Values button.
Adaptive Gridding causes the grid nodes to be shifted up to 30% of a cell width to cause the nodes to align with your input data values. By having grid node coincident with surface points, the grid will exactly honor the surface at that location. This help maintain accuracy with coarser grids.
The Min X, Max X, Min Y and Max Y inputs allow the user to define the horizontal domain within the data set in which kriging of the geologic surfaces will be completed. The Min and Max values are only used when the Rectilinear Option is selected. The Min (x-y) values are also used to set the origin for the Finite Difference Grid Type option. A value of 0 is the default for these parameters, which results in a model domain that is defined by the entire data set when the module is run. When kriging within a finite difference domain, the Min (x-y) values are used to set the origin (lower left hand corner before grid rotation). If the user is uncertain of the X and Y limits of the data domain, the module should be run with the default 0 values, and upon completion of execution, the values in the X and Y input fields will be the min and max values of X and Y in the data set. Alternatively, the Stat CSV GEO module can be used to examine the data characteristics. There is no specification of the Z grid dimensions, as Krig_3D_Geology outputs 2-D surfaces of each geologic interface. The modules that use the output of Krig_3D_Geology define the Z grid dimensions as specified by the user in those modules.
The X Res and Y Res parameters specify the number of grid nodes that will be included within the model domain. The number of grid elements along either axis of the model is simply the X Res or Y Res value minus one, as every element has two bounding nodes. The default value for these parameters is 41, but the user can specify any number desired, up to the limit of available memory resources in the computer and run time limitations imposed by the patience of the user. The robust kriging algorithms in EVS generally produce reasonable modeled distributions with a fewer number of grid nodes than the user may be used to, so the recommended procedure for setting the X and Y Res parameters is to start with less, and then increase the value until an acceptable model fidelity is obtained.
The Boundary Offset parameter sets the distance that the convex hull for the kriging domain will be set outside of the actual convex hull of the data. This parameter allows the user to specify the distance outside of the actual data in which the parameter values will be extrapolated. The distance is a percentage of the diagonal extent in the X-Y plane. The default is 0.10 (10%). For example: if data extent is 100 in x and 100 in y, diagonal distance is 144. It will make the convex hull offset 14.4 total by offsetting 7.2 on all sides. This eliminates dangerously large offsets when data extent is small.
The Default Units parameter allows the user to set the coordinate units of the model if the file being read does not contain them. If the file does contain coordinate units, this parameter is ignored.
To set up a finite difference grid, the Gridding options checkbox should be checed and the Finite Difference Grid Type should be selected, which will bring up the X and Y check boxes, and the Angle data input field. The angle input field allows the user to specify an angle in degrees counter-clockwise from true north that the resulting grid will be rotated. The finite difference grid corresponding to the input parameters can be visualized at any time by clicking the Accept All Current Values button (before a .geo file has been specified in the file browser). The Finite Difference Gridding subpanels for X and Y allow the user to constrain the modeled domain to be within the finite difference grid setup using the Krig_3D_Geology control panel. Note the X and Y values specified in these subpanels override any other specified values for Min and Max X and Y in the Gridding Options. Clicking on the X or Y subpanels in finite difference gridding brings up a subpanel similar to the one shown in the figure below.
The first parameter is a slider to specify the total Number of Steps (grid regions). There is no limit to the number of steps (regions) and each region can any number of elements (cells) and can have constant size cells, decreasing (Cx < 1.0) or increasing (Cx>1.0).
The user builds the finite difference model grid by specifying the distance between the first and second grid nodes (or the element width) in the Del X input field. The number of additional nodes to be placed at this spacing is then specified in the Xr (standing for "X repeat") input field. If a gradually varying node spacing is desired between the number of nodes specified in Xr, then a multiplication factor is specified in the Cx (standing for "Change X") input field. Values greater than 1.0 create an increasing element size, and values less than 1.0 create diminishing element sizes. The grid design process is identical for the Y grid panel. These panels allow the user to quickly design and visualize a rectilinear model grid.
The Create Computational Surface panel is shown above. This method will create three different types of surfaces based upon the created grid. A file is required for a computational surface to be created. The first step is to create the desired grid using the Gridding Options subpanel discussed above.
The Surface Type radio box is the next step. There are three different types of surfaces that can be created. The Strike Dip Plane option consists of a single surface that can be rotated to match both strike and dip values. This option also requires an 3D coordinate point to center the rotation plane. This coordinate point is entered into the X / Y Anchor fields as well as the Elevation field. A Material Number and Surface Name can also be entered for this computed surface.
The Elevation suface parameters can be seen in the image above. This surface type will create any number of surfaces all with the same X, Y coordinates created by the gridding options, but at set elevations. The Material Number and the Surface Name can be set for each surface.
The Depth surface paramets can be seen above. This method will Krige the selected file onto the grid created using the gridding options. It will then create any number of layers at specified depths below the top surface. The Material Number and Layer Name can be set for each layer.
Data Processing Options
The only parameters that affect the output shape of the resultant surfaces are:
The Pinch Factor parameter provides the ability to control where pinching occurs between positive thicknesses and borings having the pinch flag. It defaults to 1.0 which causes pinching to occur approximately half-way between positive thicknesses and borings having the pinch flag. When older applications created before version 9.5 are loaded they will have a value of 0.0 for backwards compatibility.
The Krig .GEO files in thickness space toggle off causes GEO files to be kriged like GMF files. Each surface get kriged independently of the other surface instead of being kriged in thickness space. This only applies to GEO files without the $W/$G flags.
The Spline_Geology module uses the same gridding and computational surface functionality as Krig_3D_Geology. Some of the images above are from Krig_3D_Geology because their function is identical.