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Resizing or Shrinking volume Grids can come in very handy for many reasons. Use this operator  to move a signed distance field in or out along its normals. The result of this operation is either an enlarged or shrunken signed distance field.

Operator Inputs

ON - determines whether the operator is considered 'on' or 'off'. You can connect other operators to this input channel such as a Bool Helper to activate/deactivate the whole operator.

Time -  defines the local time for the operator when the user wants to override the default system time.

DistanceField - connect a volume Grid of the type DistanceField to this input.

AlphaMask - connect any scalar field type to this input to act as an Alpha mask to restrict were Resizing happens in the volume Grid.

All remaining input parameters are identical to the UI controls. For more information about the use of an individual parameter check out the descriptions below.

Operator Outputs  

DistanceField - outputs the volume Grid with the modified result. To actually set the modified values in the distance field, this output needs to be connected to a SetGridVDB node to write all values to the grid. After a SetGridVDB node has been connected to this output the original volume Grid  will be overwritten with the filtered result.

Rollout Menu

Type - there are several options to resize the volume Grid.

  1. Dilate - expands the surface outwards along its normal.
  2. Erode - shrinks the surface inwards along its normal.
  3. Open - first shrink the surface, then expand it outwards by the same amount to remove isolated hills and islands.
  4. Close - first expand the surface, then shrink it inwards by the same amount to fill holes and valleys.

Offset - sets the distance to move the surface in or out in voxel space, unless world space is checked.

Worldspace - check this option to set the Offset value to worlds pace units and not voxel size.


Various operations on distance field volume Grids can cause the signed distances to become invalid. Renormalization takes care of this. After each Morphing step, the signed distance field is iteratively reset with its new values. This process also takes spatial and temporal sampling into account.

Iteration - sets the amount of iterations or passes a renormalization step should use to straighten out everything.

Spatial Scheme - sets the interpolation method for the space between voxels in the volume Grid. The options further down the list are more accurate but take more time. There is no general guide line of what to choose it depends on the field values and scale as well as on the type of distance field.

Temporal Scheme - getting from one voxel in space to another is not only defined by the gap (distance or space) in between. This parameter lets you choose how accurate the time sampling of the velocity field should happen. Same rule, here: the further down the list is more accurate but takes more time.

Trim - allows you to select from different trim options for voxels that fall outside the narrow band.

  • None - leaves out-of-band voxels intact.
  • Interior - sets out-of-band interior voxels to the background value.
  • Exterior - sets out-of-band exterior voxels to the background value.
  • All - sets all out-of-band voxels to the background value.

Alpha Mask

Using a volume Grid as an Alpha mask helps in defining were the Morphing effect should be applied to in the 3D volume.

Invert - check this option to invert the connected AlphaMask

Min - defines the lower threshold of the Alpha mask values.

Max - defines the upper threshold of the Alpha mask values.

©2024, cebas Visual Technology Inc.

reference_guide/thinkingparticles_nodes/operator_nodes/openvdb_sdf/resizevdb_operator.txt · Last modified: 2024/01/24 18:34 by

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