Sample a Surface onto a Grid

Use the Sample a Surface onto a Grid option (geogxnet.dll(Geosoft.GX.Surface.SampleASurfaceOntoAGrid;Run)*) to sample a surface (mesh) onto the geometry of an existing grid, so that you can use the new grid in other processes that do not support meshes. The GX takes a geosurface file, a selected surface, and a geometry grid (regular or plan orientation) as inputs. A new grid is created with the same parameters as the geometry grid.

You can access the option from the following locations:

The Geosurface > Utilities menu
The 3D View > Geosurface > Utilities menu
The 3D Viewer Geosurface > Utilities menu

Sample a Surface onto a Grid dialog options

Input geosurface file	Select the "source" geosurface file. The geosurface must have a valid coordinate system defined. Script Parameter: SAMPLE_SURFACE_ONTO_GRID.GEOSURFACE_FILE
Surface to sample	All the surfaces contained in the input geosurface are listed. Expand the drop-down list and select the surface to sample. Script Parameter: SAMPLE_SURFACE_ONTO_GRID.SURFACE_NAME
Geometry grid	The orientation and geometry of the sampled grid will be determined by using the location, geometry, and coordinate system of an existing "geometry" grid. Supply an existing grid on which to sample the mesh. The geometry grid must have a "normal" or "plan" orientation and a valid coordinate system (CS) defined. Once a geometry grid is selected, the geometry parameters are displayed in the section that becomes visible when you click the More button. Script Parameter: SAMPLE_SURFACE_ONTO_GRID.GEOMETRY_GRID
Output grid	Specify a new output grid file, or select an existing "destination" grid file (an overwrite confirmation message will display in this case). The output grid will inherit the geometry and coordinate system from the geometry grid. Script Parameter: SAMPLE_SURFACE_ONTO_GRID.OUTPUT_GRID
Cell value	The GX calculates the intersection(s) of a vertical line at each cell center with the surface: you can choose whether the output grid cells are populated with the elevation of the top intersection, the bottom intersection, or the average of all intersections: "First intersection from the top": the maximum value. "First intersection from the bottom": the minimum value. "Average of all intersection": the mean value. By default, the mean Z value of the mesh at each grid node (X,Y) is used to populate the grid. If the mesh is valid at the center of a grid cell (i.e., the cell center falls on or within the (X, Y) bounds of a triangle), the cell should be filled with valid data in the output grid. If the center of an input grid cell does not fall on or within (i.e., it is outside of the (X, Y) bounds of valid triangles), the output grid value for that cell is "dummy". Script Parameter: SAMPLE_SURFACE_ONTO_GRID.PROJECTION_METHOD [0: maximum, 1: minimum, 2: mean]
[More]	Click on the button to display the Grid geometry parameters: the coordinate system information and the (X, Y) cell size, number of cells, and grid origin.

Application Notes

*The GX tool will search in the "...\Geosoft\Desktop Applications \gx" folder. The GX.Net tools, however, are embedded in the geogxnet.dll located in the "...\Geosoft\Desktop Applications \bin" folder. If running this GX interactively, bypassing the menu, first change the folder to point to the "bin" folder, then supply the GX.Net tool in the specified format.

This GX bridges the gap between Wireframing and other surface-based modelling programs (e.g. GOCAD) and grid-based modelling packages like GM-SYS 3D. For example, you can now sample one or more horizons (meshes), created by wireframing multiple GM-SYS Profile models together, onto the geometry of your DEM, and use the grids to build a GM-SYS 3D model.

The GX assumes that the mesh defines a sub-horizontal lithologic boundary that is laterally continuous and converts it to a grid that can be used in processes that utilize grids as boundaries. You can use DXF or GOCAD surfaces, or any other meshes in your project to convert them into grids.