If the lattice controlling the Isosurface is input "A" and the GRD of the geologic surface is input "B", then the following equations change the value of the lattice to the negative value based on the geologic surface GRD.
IF Z > B, A, -A Or Z > B? A:-A
The graphic below illustrates a Network window with a Gridder output lattice and a GRD file. Isosurface 1 (output disabled) is the output from the Gridder without modification, and Isosurface 2 (blue) and Isosurface 3 (orange) display the output from the Math module. The HeightField (gray) displays the output from the GRD file without modification.
Updated September 20, 2018