INTERPEX Limited IX1D. Interpex's IX1D packages provide forward and inverse modeling capabilities for resistivity and terrain conductivity data. The software is menu driven and widely used by geophysical companies involved in environmental and geotechnical assessment activities. The demo version of the IX1D software and class files can be downloaded here to Northwest Geophysical Associate's software package GM-SYS are suggested to use for gravity and magnetic modeling. This software provides 2D and limited 3D (2 & 3/4) forward and inverse modeling capabilities. For more information about Northwest Geophysical Associates, visit hhttp://www.nga.com.ttp://www.nga.com.