Starting Model

Use the options Constraints > Add Constraint > Starting Model or Starting Model > Modify to provide an initial voxel model or to replace an existing one.

Modify Starting Model Constraint dialog box options

 

Constraint type

By Default, the starting model is set to zero for all voxel elements. If the inversion model type is MVI, then all three components of the vector voxel model elements are set to zero.

For all model types other than MVI, you may provide a Constant other than zero for the entire model. Use this option to calculate the terrain effect at a given density. Alternatively, if you have derived a plausible Voxel model for the study area through earlier processes, you may choose to provide it instead.

For the MVI model types, the Constant option is not available because it is conceptually difficult to derive. However, if you have created a plausible Vector Voxel model for the study area through earlier processes, you may select it.

Filename

If theVector Voxel option for MVI or the Voxel option for the other model type has been chosen, you are prompted to provide the name of the file that defines the gradient model. This file is re-gridded to the VOXI document mesh interval and extrapolated to the extents of the padded mesh.

Application Notes

The starting model is often chosen to be the same as the Parameter Reference Model.

  • If you used the New VOXI from Voxel tool to create this VOXI document, then the voxel file you supplied initially will be shown here as the Starting Model.

    • The starting model should be supplied to run a forward model. However, this model cannot be all zeros.

    When running an inversion, the starting model is the model with which the first iteration begins and as such is not an explicit constraint. Nevertheless, it may affect the final model reached by the inversion so it may be considered an implicit constraint.

  • A good starting model will speed up the inversion and generate results faster. It is perfectly permissible (and common practice) to choose a uniform earth as the starting model when no other information is available.

    • Access Seequent Online Learning and select the VOXI guided paths to learn more about effective workflows and key concepts.

    See Also: