This technical tip will help you understand how to create a high quality fitting surface.

Step 1: Mesh Optimization

To get a high quality fitting surface, you will first need to prepare the mesh through some optimization processes. If the size of the poly-faces is regular and the resolution of the mesh is high enough, you will be able to fit a more ideal surface.

How to optimize a mesh to get a high quality fitting surface:

Note: XOR provides you with several methods to optimize a mesh from its current state, such as Healing Wizard, Fill Hole, Smooth, Enhance Shape, Optimize Mesh, etc.

If some abnormal faces and various defects exist in the mesh, you can easily find and clean them with the Healing Wizard command.
If some holes exist in the mesh, you can easily close them with the Fill Holes command.
You can also enhance the quality of the mesh using the Enhance Shape and Optimize Mesh commands.

1. Double-click the mesh, or click on the “Mesh” mode button in the Tool Palette, to enter Mesh Mode.

2. Click the “Healing Wizard” button or click Tools > Mesh Tools > Healing Wizard.

3. You can check which kinds of defects are in the mesh and how many there are, as shown in the image below.

4. Click the OK button

Note: The Healing Wizard automatically heals various defects in the mesh.

Folded Poly-Faces – If checked, folded poly-faces will be deleted.
Dangling Poly-Faces – If checked, you will remove any 2 or 3-sided open poly-faces.

Small Clusters – If checked, you can set a value for the Maximum Face Count In A Cluster; then all clusters (a group of connected poly-faces) that have less than the specified number of poly-faces will be removed.

Small Poly-Faces – If this is checked, you can input a value in the “Area Is Smaller Than” box, and poly-faces whose areas are smaller than this value will be removed.

Non-Manifold Poly-Faces – If checked, non-manifold faces and redundant poly-faces will be removed.
Crossing Poly-Faces – If checked, all the crossing faces will be removed. There are three methods: The Smooth method smoothly regenerates poly-faces around the crossing poly-faces. The Merge Poly-Vertices method merges poly-vertices around the crossing poly-faces. The Delete And Fill Hole method removes poly-faces around the crossing poly-faces and fills in the hole(s) there.

Small Tunnels – “Small tunnels” means that the poly-faces’ shape is constructed as a tunnel or handle. If Small Tunnels is checked, you can adjust the Poly-Face Count In Tunnel box. Then the tunnel faces whose number to the tunnel direction is shorter than this value, will be removed.

5. Click the “Defeature” button or click Tools > Mesh Tools > Defeature.

6. Select the Flat option as the “Method” and select a region to remove features and fill faces in that region, as shown in the image below.

7. Click the OK button.

Note: “Defeature” removes the selected poly-faces and fills in the space based on adjacent poly-face information.
If you want to re-form the feature after you generate whole surface body, you have to prepare a feature profile beforehand.
Another way to do this is, before Defeature operates, to copy the original feature into its own new mesh using Copy (Ctrl + C) and Paste (Ctrl + V). You will then be able to work with it later.

Note: You can fill faces in the missing area using “Fill Holes” or clicking Tools > Mesh Tools > Fill Holes.

8. Click the “Optimize Mesh” button, or click Tools > Mesh Tools > Optimize Mesh.

9. Select the “High Quality Mesh Conversion” option as the Method, and adjust the options as shown in the image below.

10. Click the OK button.

11. Check the result.

Step 2: Create Boundary Curves

Secondly, you can prepare boundary curves to create a fitting surface on the mesh. If the number of curve boundaries is 4 and the shape is a regular rectangular feature, you will get a better fitting surface.
Otherwise, a fitting surface will be twisted and have some self-intersection(s).

How to organize boundary curves to get a fitting surface:

Create 3D Mesh Sketch
• Create boundary curves which can keep the equilibrium of forces
• If the number of boundary curves is 4 and its shape is a regular rectangular feature, you will get abetter fitting surface, as shown in the image below.

• Even though you can keep that the number of boundary curves at 4, if its shape becomes suddenly narrow or twisted as shown in the image below, twisted and self-intersected faces could be created when the surface is generated.

Match Boundary Curves
• If possible, avoid “T-Junction” matching when you create curve networks
• If not, organize “T-Junction” matching so that the curve networks can keep the equilibrium of forces as shown in the image below.

• Other than the 4 sides of the curve boundary, others will create a trimmed fitting surface.
• If trimmed surfaces are neighbored with the same matching boundary, those will not be matched.
• Organize the curve network so that the surface matching conditions can be applied.

For Example:
Untrimmed Surface – Untrimmed Surface
Untrimmed Surface – Trimmed Surface – Trimmed Surface
Untrimmed Surface – T-junction matching – Untrimmed Surface

• If possible, setup the same number of control points in the each matching boundary of the surface patches to improve surface matching continuity.
• If possible, setup the boundary curves using appropriate control points to apply the fitting operation.

Create Curve Network
• If the shape is going sharp or dull, you can manage the number of curve boundaries according to the shape, as shown in the image below.

• If a fitting curve is not correctly put on the mesh, an accurate fitting surface cannot be created.
• In that case, increase the number of control points on the curve using the “rebuild” option

Step 3: Create a Boundary Fit Surface

Finally, you can create a fitting surface using the pre-defined boundary curves.
However, even if the curve networks are well organized on the mesh, the fit surface will be created a bit differently, according to the defined fitting options.

How to use options to get a high quality fitting surface:

Boundary Fit operation has been separated into 2 stages:
• In the first stage, you can set Mesh Curves, Curve Loops, and Loop options.
• In the second stage, you can define sharp edges to keep the sharpness at the boundary, as well as the number of control points in the surface to be created. This is shown in the image below.

1st Stage (Setup Curve Loops):
• Allow Hole (Boundary) – If this option is turned on, the surface will be created even though a hole exists inside the boundary of the curve, as shown in the image below.

• Allowable Convex Ratio – In the case that some feature(s) exist inside the loop, this option allows you to create a surface using a Convex Ratio.

2nd Stage (Adjust Fitting Options):
• Set Resolution – you can adjust the resolution of a surface patch via “Number of Control Points” or “Allowable Deviation.”
  • If possible, set the same number of control points along the U and V directions, as you can get a better surface body that way.
  • Using “Set Manually,” you can easily set the control points along the U and V directions of a surface patch, as shown in the image below.

• Set Sharp Edge – Use this option if a sharp area exists in a mesh, or if you need to keep the sharp feature on a surface body.
  A position matching operation will be applied to the boundary only.
  In this way, you can preserve the sharp edge in the surface body you’re creating and modify it whenever you want.

• Resample – If this option is turned on, the fitting area will be regularly simplified and a smoother surface will be generated.
  However, you can decide whether you turn the option on or not according to your particular application.
  If you want to generate a surface body as close as possible to the mesh (“as is”), even if the resulting shape would have positive or negative complex features like under-cut areas, turn off this option.