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Partial Shell applies a shell offset with a non-uniform offset distance: it builds a shell around the mesh with a base thickness everywhere and a larger thickness in the regions you save. Use it when the shell must not be equally thick across the whole surface. For a shell of one thickness, use the Shell mode of Offset; to move the vertices of a mesh quickly without building a shell, use Fast Offset.
To open the tool, select exactly one mesh, go to Mesh Edit, click the arrow next to Offset and choose Partial Shell.
Partial Shell: Parameters
Once the Partial Shell tool is activated, the Partial Shell panel appears on the right. From there, you can configure how the shell offset should be applied to the selected mesh.
The upper part of the panel defines how the general offset is applied to the whole mesh.
Global Offset defines the base offset distance applied to the entire mesh. This value sets the main shell thickness before any additional regional offsets are specified. It cannot be smaller than 0.7 × Voxel Size.
Two-Sided controls whether the shell is built on both sides of the original surface. It is on by default. If this option is disabled, Partial Shell builds only the positive part of the shell.
Voxel Size defines the size of the cubical voxel used during the operation. MeshInspector suggests a value from the size of the mesh when the panel opens. A smaller voxel size produces a more detailed result but takes more time and memory, while a larger value produces a coarser result.
Interpolation controls the smoothness of transitions between regions with different offset values. A larger value makes the transition between the region offsets smoother. The default is 1/20 of the diagonal of the bounding box of the mesh.
Variatic Regions
The Variatic Regions section (regions with their own offset) lets you select a region on the mesh to specify an additional offset there. This is what allows Partial Shell to create a non-uniform shell thickness.
First, select the area of the mesh where the additional offset should be applied. To do this, go to the Select tab and click Select Primitives. You can use any available selection mode, depending on the shape and size of the target area. In this example, we use the Rect selection mode to select the lower part of the bust. The selected area is highlighted directly on the model in red.
The Partial Shell tool remains active while you work with the selection tools, so you can define the region without closing the Partial Shell panel. After the required area is selected, go back to the Partial Shell panel and click Update Region (the button appears only when the mesh has selected triangles). This saves the current mesh selection as a variatic region. The first region you update is saved as 1 in the Regions dropdown list.
To add more regions:
- Return to New Region in the Regions field.
- Select the area for your new region.
- Click Update Region again.
The new regions will be saved as 2, 3, 4, and so on. In the screenshot above, we selected the upper part of the mesh by applying Inverse Selection under the Select tab.
For each region, Additional Offset defines the extra offset applied to it. This value is added to the Global Offset, allowing the selected area to receive a different shell thickness from the rest of the mesh; it also cannot be smaller than 0.7 × Voxel Size. Only saved regions count: a selection for which you did not click Update Region gets only the Global Offset. After configuring the global offset and the variatic region settings, click Apply to create the partial shell.
The result is a new object named after the original plus shell; the original mesh is hidden and deselected. The saved regions receive the additional offset, while the rest of the mesh follows the general shell settings. In the example below, you can see the result of a Partial Shell operation with:
- Global Offset at 0.697 mm.
- Additional Offset applied to the lower part at 1 mm.
- Additional Offset applied to the upper part at 2.5 mm.
To see what has happened inside the model, we used Mesh Edit › Section and drew a plane. As you can see, the shell thickness in the upper part is clearly greater than in the lower part, just as intended.
