Module: Surface Edition ()

Description:

The surface edition allows you to modify a triangular surface in several ways, e.g., to remove or refine triangles, to flip edges or move points, or to set boundary ids for individual triangles. It also allows you to check a surface for intersecting triangles or for falsely oriented patches. A basic concept of the surface edition is the notions of visible and highlighted triangles respectively. Highlighted triangles are drawn in red wireframe. Many tools operate not on the surface as a whole, but only on highlighted triangles. For example, if you want to refine parts of the surface, you'll first have to highlight the involved triangles before choosing Refine faces from the Edit port.

Connections:

Data [required]
The surface to edit and test.

Ports:

Manipulation

Choose between edit or test actions on the surface.

Edit

• Undo: Undoes the last edit operation (edge flip, edge collapse, edge bisection, vertex movement). Selection and highlight changes can be undone as well. The size of the undo buffer is limited to 100 entries.
• Delete highlighted faces: Permanently removes the highlighted triangles from the surface.
• Remove coplanar faces: Permanently removes coplanar triangles, i.e., triangles with the same three vertices, from the surface. The inner region and outer region id of the remaining triangle is updated appropriately.
• Recompute connectivity: Recomputes the surface's connectivity information, i.e., contours and branching points. Connectivity information is optional. If it is present, contours can be displayed using the Surface Patch Contours module. In addition, recompute connectivity causes unused points of the surface to be deleted.
• Refine faces: Subdivides all highlighted triangles by bisecting their edges. Each refined triangle is replaced by four new ones. In addition, adjacent non-highlighted triangles are split in two in order to avoid dangling nodes.
• Smooth faces: Smoothes all highlighted triangles by shifting their vertices. Each vertex is shifted towards the average position of its neighbors. Special care is taken in the case of boundary vertices, for which not all the neighbors are considered, but only those that are also on the boundary. In this way sharp boundaries are preserved.
• Flip edges...: Pops up a dialog allowing you to flip certain edges inside the highlighted part of the surface. The edge flips are performed in order to improve the aspect ratio of the involved triangles. An edge flip is only attempted if the aspect ratio of one of the two involved triangles is worse than a user-specified value, and the crease angle between them is below a user-defined threshold.
• Reorder patches...: Pops up a dialog allowing you to rearrange the internal order of the surface patches. Two different patches can be selected and then swapped. This operation is useful for certain applications where two different surfaces are required to have the same patch structure.
• Set boundary ids...: Pops up a dialog allowing you to edit the surface's boundary ids. The dialog permits you to define new boundary ids or to change existing ones (including the preferred colors). Highlighted triangles can be assigned a new boundary id using the dialog's set button.
• Fix intersections...: Pops up a dialog for an automatic repair of intersecting triangles. The total number and the number of fixed intersections will be shown in the console window.
• Fix small dihedral angles...: Pops up a dialog for an automatic repair of small dihedral angles. The dialog offers two different repair modes: vertex smoothing, and a combination of edge flips and vertex shifts. The dialog lets you define a lower bound for the dihedral angle.
• Fix tetra quality...: This tool provides an automatic repair of configurations which might induce large tetrahedron aspect ratios. It pops up a dialog where you can specify an upper bound and an attempted value for the tetrahedron aspect ratio.
• Prepare Generate Tetra Grid...: This tool may be useful if you want to create a tetrahedral volume mesh from the surface. It combines the Flip edges, Fix small dihedral angles, and Fix tetra quality tools. You can specify a lower bound and an attempted value for the tetrahedron aspect ratio.
• Fill Hole...: This menu entry shows a drop-down menu in the properties panel with a selection of hole fill algorithms. By pressing the fill button the currently displayed hole is triangulated using the selected hole fill algorithm.
• Magic wand settings...: This menu entry pops up a dialog alowing you to change parameters of the magic wand tool.

Test

• Materials: this selector allows you to highlight parts of the surface separating two particular regions from each other. The two regions are specified in two additional combo boxes which are shown once the selector is activated.
• Boundary Conditions: Highlights all triangles with a particular boundary id. The boundary ids defined in the surface are listed in a separate combo box. Boundary Conditions can be modified using the Set boundary ids... action of Edit port.
• Patches: Highlights all triangles belonging to a particular patch of the surface. The different patches can be selected using a slider displayed right beside the selector combo box. A patch is a group of triangles separating the same two regions and having the same boundary id.
• Intersection test: Performs an intersection test and highlights intersecting triangles. The compute button actually initiates the test, while the back and forward buttons allow you to cycle through the list of intersecting faces. The total number of intersections is printed in the console window. Intersections can be repaired automatically using the Fix intersections action from the Edit port, or manually using the edit tools (edge flip, edge collapse, edge bisection, vertex movement).
• Closedness test: Performs a closedness test and highlights those triangles where the test fails. This test should not be applied to surfaces with several adjacent materials for which it will falsely report closedness errors.
• Orientation test: Performs an orientation test and highlights falsely oriented triangles. You should have removed all intersections before applying this check. For simple configurations the wrong triangles are removed automatically. The number of inconsistently oriented triangles and the number of removed triangles are printed in the console window. If the automatic method could not remove all incorrect orientations, you can proceed as in the case of intersections and try to repair them manually. Important: A prerequisite for the orientation test is that the outer triangles of the surface be assigned to material Exterior. If the surface does not contain such a material or if the assignment to Exterior is not correct, the test will falsely report orientation errors. This test can be applied to surfaces with multiple adjacent materials.
• Aspect Ratio: sort all surface triangles according to the quality measure. The aspect ratio is the ratio of the radii of the circumcircle and the incircle of a triangle. The largest aspect ratio should be below 20 (better 10). The worst triangle according to the selected quality measure is displayed, and the worst quality is printed in the console window. Using the back and forward buttons right beside the selector combo box you can cycle through all other triangles and edit the surface if necessary. In the Edit port, Flip edges can automatically improve the quality measure.
• Dihedral Angle: sort all surface triangles according to the quality measure. The dihedral angle is the angle between two adjacent triangles at their common edge. The smallest dihedral angle should be above 5 degrees (better 10). The worst triangle according to the selected quality measure is displayed, and the worst quality is printed in the console window. Using the back and forward buttons right beside the selector combo box you can cycle through all other triangles and edit the surface if necessary. In the Edit port, Fix small dihedral angles can automatically improve the quality measure.
• Tetra Quality: sort all surface triangles according to the quality measure. Tetra Quality may be useful if you want to create a tetrahedral volume mesh from the surface. For each surface triangle, the aspect ratios of the tetrahedra which will probably be created for that triangle are calculated. The largest tetrahedral aspect ratio should be below 50 (better 25). The worst triangle according to the selected quality measure is displayed, and the worst quality is printed in the console window. Using the back and forward buttons right beside the selector combo box you can cycle through all other triangles and edit the surface if necessary. In the Edit port, Fix tetra quality can automatically improve the quality measure.
• Non-manifold test: This test detects non-manifolds on surfaces and displays every non-manifold location including the incident triangles.
• Holes test: This test detects holes on triangular meshes, which can be closed by the triangulators available from the Fill Hole... action of the Edit port.