Select UseManual to use the structure generation parameters given in the Overlay Grains and Gauss Field Settings, Grain Generator, and Random Field panels as starting point for the optimization.

Select GlobalOptimizer to run a global optimization to find good initial parameters for the local optimizer. In this case the values selected in the Overlay Grains and Gauss Field Settings, Grain Generator, and Random Field panels are not used.

In this panel you setup the initial structure for the local optimization.

The Overlay Strength is the field overlay strength in percentage. At 100% overlay strength the result will only show the grain package, while at 0% overlay strength the result will show only the Gaussian random field. If no Random Field is used, this value is automatically set to 100%. If no Grain Generator is used, this value is automatically set to 0%.

Select the basic shape used to generate the 3D structure. Select None as Grain Generator to use only the Gaussian random field for the structure generation. The app uses the GrainGeo - Create command to create the grain structure. Be aware that all lengths are given in the unit voxel.

The values entered for diameters, standard deviations and aspect ratios define the initial structure for the local optimization. They are only used if UseManual was selected for Initial Parameter Values.

For the Sphere shape, the diameters are Gaussian distributed. Select the mean diameter and the standard deviation.

For the Ellipsoid shape, the first diameter is Gaussian distributed. Select the mean diameter and the standard deviation. For the other two diameters, fixed aspect ratios are used.

For the Convex Polyhedron shape, an ellipsoid is used as enclosing object. Select the mean diameter and the standard deviation. For the other two diameters, fixed aspect ratios are used.

Select None as Random Field to use only the Grain Generator for the structure generation.

The values entered for correlation length(s) and relative influence define the initial structure for the local optimization. They are only used if UseManual was selected for Initial Parameter Values.

Select OneIsotropicGauss and enter the Correlation Length to use the GrainGeo - Stochastic Field Thresholding command to create a Gaussian random field with the Isotropic Gaussian Generation Mode.

Select TwoIsotropicGauss to use the GrainGeo - Stochastic Field Thresholding command to create a Gaussian random field with the Custom Generation Option using two Isotropic Gaussian kernels. You can define the Relative Influence of the first Gauss kernel, and give both Correlation Lengths.

The error function is a combination of several components. Define the error function components from the list of physical properties. These structure properties will be matched by the twin as good as possible.

Select Pore and Solid Granulometry to use the PoroDict - Pore Size Distribution (Granulometry)  and MatDict - Solid Size Distribution commands to compare the digital twin with the original 3D image.

Select Porosimetry to use the PoroDict - Pore Size Distribution (Porosimetry) command to compare the digital twin with the original 3D image.

Select Pore and Solid Chord Length to use the PoroDict - Chord Length Distribution and MatDict - Chord Length Distribution commands to compare the digital twin with the original 3D image.

Select Specific Surface Area to use the MatDict - Estimate Surface Area command to compare the digital twin with the original 3D image.

Select Permeability to use the FlowDict-Stokes command to determine the permeability. Select the space directions used to compare the digital twin with the original 3D structure. To use this option, a FlowDict license is required.

Select Diffusivity to use the DiffuDict - Bulk Diffusion command to determine the diffusivity. Select the space directions used to compare the digital twin with the original 3D structure. To use this option, a DiffuDict license is required.

You must select at least one of these criteria, otherwise the optimizer will fail with an error message.

Select the sets of parameters to be used as optimization variables for fitting the reference structure. If not selected, the according parameters from the Digital Twin Setup will stay constant during the optimization.

Select Optimize Overlay Strength to vary the Overlay Strength.

Select Optimize Grain Generator Parameters to vary the diameter, standard deviation and aspect ratio parameters of the Grain Generator. Note that the optimizer does not optimize the generator type, i.e. does not vary between Sphere, Ellipsoid and ConvexPolyhedron shapes.

Select Optimize Random Field Parameters to vary the correlation length(s) and the relative influence parameters of the Random Field. Note that the optimizer does not vary between the OneIsotropicGauss and TwoIsotropicGauss models.

You must select at least one of these options, otherwise the optimizer will fail with an error message

Set the stopping criterion by choosing a maximal number of iterations or set a tolerance accuracy to reach. Note that choosing none or setting the Maximal Number of Optimization Iterations to 0 will perform one single iteration step only.

The selected tolerance applies to the structure generation parameters varied in each iteration step. If the change in these parameters becomes smaller that the selected tolerance, the optimizer stops. The tolerance does not set a limit value for the resulting error function of the found digital twin.

Check the box to set the size of the generated 3D structure model.

If the box is not checked, the size of the reference structure is used.

If checked, all intermediate results are deleted.

Activating the check box enables to set one additional parameter.

Check Invert Grains for Overlay to switch pore and solid material. In this case, the grain generator creates the pore space, and the background becomes the solid material.