1. In the Network Editor, create a new Topo Transfer SOP node.

2. Connect the source geometry’s node to the first input on the Topo Transfer node and the target geometry’s node to the second input.

3. Turn on the Display flag for the Topo Transfer node.

   The undeformed template geometry appears in the viewport and a warning appears on the Topo Transfer node.

   

   Before the Topo Transfer node can cook, it first needs at least one valid landmark point pair. A landmark point pair is not valid until you set the position of its target point.

   Note

   If you want to cook the Topo Transfer node without using landmark points to improve the quality of the deformation, you can disable landmark groups by turning off the Enable Landmarks parameter on the Topo Transfer node.

4. In the Network Editor, make sure that the Topo Transfer node is selected, hover your mouse pointer over the viewport, and then press Enter.

   The following occurs:

   • A new landmark group is automatically created for your Topo Transfer node.

   • You are now in the edit state for that landmark group.

   • The Landmark toolbar appears across the top of the viewport, and the new landmark group’s name appears in the Group Name toolbar field.

     This toolbar contains the controls that allow you to create landmark groups and edit landmark group point correspondences.

     Since you are in the edit state, the landmark group edit options for the current landmark group appear in the toolbar.

   • The template landmark guide mesh appears in the viewport.

   • A new landmark group appears under Landmarks in the Topo Transfer node’s parameters. Each landmark group contains one or more landmark point pairs.

   Tip

   You can also create landmark groups by clicking the Create Group button in the Landmark toolbar or the Landmarks > Landmark Groups > + button in the Topo Transfer node’s parameters.

   Note

   If you create a landmark group through the Topo Transfer node’s parameters instead, then you can only directly enter the edit state for that group by clicking its Edit Landmark Group button.

5. Rename the new landmark group.

   In the Landmark Group toolbar, click in the Group Name field, type the new name for the landmark group, and then press Enter.

   

   Tip

   You can also rename a landmark group using the Landmarks > Landmark Groups > Name field in the Topo Transfer node’s parameters.

6. In the viewport, -click the locations on the template guide mesh where you want to place the landmark point pairs.

   The new landmark point pairs automatically snap to the template guide mesh’s surface. You can freely -drag the landmark point pairs to any location on the guide mesh, not just its polygonal indices.

   A landmark point pair consists of a template point and its corresponding target point. Initially, a target point has the same location as its corresponding template point.

   Tip

   • You can delete a template point or a target point by -clicking on the point in the viewport. Deleting a template point deletes its landmark points pair.

   • You can reposition the template guide mesh using the translate handles.

   

7. Press G to switch to viewing the target guide mesh.

   Tip

   You can also use the Show drop-down menu options in the Landmark toolbar to switch between viewing the template and target guide meshes.

   A green ring appears around the current active template point. Your next click on the target guide mesh will place the target point for that active template point.

   

   Note

   The green ring only dictates target point placement order when using -clicks to place points. You can place target points in any order by -dragging them instead.

8. For your landmark point pairs, do the following:

   • Click the locations on the target guide mesh you want to move the target points to. The target points automatically snap to the target guide mesh’s surface.

   • -drag the landmark point pair to move its target point to the desired location on the target guide mesh. The target point automatically snaps to the target guide mesh’s surface.

     Note

     • When you have multiple landmark point pairs, you can -drag their target points in any order. The green ring only dictates placement order when -click placing target points.

     • Where you can move the target point to on the target guide mesh is determined by the Target Points Group and Target Point Coordinates parameter settings. By default, you can freely -drag the target points to any location on the target guide mesh, not just its polygonal indices.

   When in the edit state, template points always appear as green circles, target points always appear as light blue squares, and dashed lines appears between the template and target points to indicate their landmark point pair relationships.

   Tip

   • You can change the color of all the landmark point pairs in a landmark group with the Landmark Group > Color parameter. This only specifies the color the points appear as when in the landmark group state, not the color they appear as when in the edit state.

   • To see a transparent version of the template guide mesh while viewing your target guide mesh, turn on Show Source Silhouette in the Landmark toolbar.

9. When you have finished editing the positions of the template and target points in the landmark group, click Done Editing in the Landmark toolbar or press Enter to save your changes and exit the edit state.

10. In the Landmark toolbar, click Solve to trigger the cook (solve) for the node.

    The following occurs:

    • The progress of the solve appears at the bottom of the Houdini window.

    • The output geometry appears in the viewport.

      

    Note

    You can also trigger the solve from the edit state.

    Now that you can see the output geometry from the topo transfer operation, you can refine its deformations.

11. Repeat steps 4-10 for each landmark group you want to create.

12. For areas of the template mesh or target mesh that have greater detail, add extra landmark point pairs to those areas.

    This increases the registration in those mesh areas and improves the quality of the output geometry.

    For example, for detailed humanoid models, the areas around the eyes, nose, ears, and mouth require greater attention during the topology transfer process to produce a more accurate deformation result.

    Warning

    Do not apply too many landmark point pairs as this will constrain the solve too much and may produce the opposite effect of what you are trying to achieve.

13. For areas of the template mesh that you want to exclude from the solve, use the Rigid Primitives parameter to specify which primitives to ignore:

    • Use the Rigid Primitives drop-down list to select existing primitive groups. You can select multiple groups.

    • Use the Rigid Primitives select geometry tool (arrow button next to the parameter) to select the primitives in the viewport.

      • ⇧ Shift + to add primitives to the selection.

      • ⌃ Ctrl + to remove primitives from the selection.

      

    Tip

    You can select both rigid primitive groups and individual primitives.

    • Press Enter to save your selection, exit the rigid primitives edit state, and trigger the cook (solve).

      The improved output geometry appears in the viewport.

      

    • Similarly, the Rigid Mask parameter lets you specify a weighted scalar as a percentage of exclusion for each point. Weighted exclusion may be combined with rigid primitives or used independently.

      • Select 'MaskOn' from the Mask Mode parameter.

      • Click the attribute paint button to enter attribute paint mode to create a weight map, or specify an existing mask attribute from the drop-down list.

      • The Mask Tolerance parameter lets you specify the amount of precision to use when comparing weights to one which is when a point is fully rigid.

      

14. Adjust the Topo Transfer node’s parameter settings as needed.

Scenario

You have a 3D scan and it is missing areas of its geometry or it has areas that you don’t want to capture. For example, the back of the head is missing from your 3D head scan or you don’t want to transfer the topology of the subject’s hair from your 3D head scan.

Solution

Use Rigid Primitives to specify which primitives or primitive groups on the template mesh you do not want to deform to the target mesh.

Scenario

The pose of your target meshes differs greatly from that of your template mesh. For example, the target body mesh’s arms are at its sides and the template mesh is in a T-pose. Or your template mesh is an open palm but your target hand scan is closed in fist.

Solution

Set the solver type to Non Linear and use landmark groups.

The Non Linear solver handles deformations that require large rotations much better than the Linear solver.

When the points on the target and template meshes are very far apart, adding landmark point pairs to the node helps the solver match the points on the template mesh to those on the target mesh.

Scenario

The template contains multiple disjoint islands.

Solution

Toggle on Enable Geometry Constraints, and optionally specify the main island which should act as a parent for the rest of the islands using the Manual option in the Constraint Selection parameter.

Note

When Enable Geometry Constraints is active, the Reduction Factor allows only an initial percentage for the start of the range because, in this case, no polygonal reduction is used at the end of the range.

Note

The automatic Constraint Selection will simply assume the island with the largest point count is the main geometry. When this is not the case, the main geometry must be specified manually.

Scenario

Landmark information for template and target geometry already exists in the network outside the Topo Transfer node.

Solution

• Connect the template landmarks to the third input on the Topo Transfer node.

• Connect the target landmarks to the fourth input on the Topo Transfer node.

• If the correspondence between the two sets of landmarks is established by labels stored as string attributes defined on the template and target landmarks, then toggle on the Use Landmark Attribute and specify the attribute that contains the label information.

  Note

  If no attribute labels are provided, Topo Transfer will assume the corresponding landmark pairs are ordered sequentially between the two lists.

  Tip

  For more information about creating externally defined landmarks, see the help page for Topo Landmark.