From Surface Mesh to Geometry: STL Import of a Vertebra

Notice that after the import completes you can no longer see the reference to the STL file in the window. The source for the geometry import is now , which is where the mesh import can be found. The node in the geometry sequence handles the last steps of the process: conversion from mesh to geometry, and creation of a solid object.

Click to locate the source mesh in the window.

Mesh Part 1: Length Unit

The sequence is added under the node. The output of a mesh import sequence added here can be imported into any geometry sequence in the mph file.

The meshing sequence in a Mesh Part has a length unit, just as a geometry sequence. Since STL files do not include units, the length unit is set to the default geometry length unit, meter.

In the window, under click .

In the window for , locate the section.

Select the check box.

From the list, choose .

Geometry 1

Although the length unit of the sequence now has the correct value, you also need to update the length unit of the Geometry 1 sequence. One way to avoid to update both is to set the length unit of the geometry sequence before importing the file.

In the window, under click .

In the window for , locate the section.

From the list, choose .

In the toolbar, click . This will update the length unit of the sequence, and re-import the geometry from the mesh.

Now modify the orientation of the geometry to improve the visualization.

Rotate 1 (rot1)

In the toolbar, click and choose .

Select the object only.

In the window for , locate the section.

In the text field, type 90.

Locate the section. From the list, choose .

Click .

Click the button in the toolbar.

Rotate 2 (rot2)

In the toolbar, click and choose .

Select the object only.

In the window for , locate the section.

In the text field, type -90.

Click .

Click the button in the toolbar.

Mesh 1

A first step to assess the quality of an imported geometry is to create a mesh. Problem regions, for example small faces or short edges, are detected and reported by the mesher.

Warning 1

In the window, under right-click and choose .

Two short edges, which are listed in the node that appears, have been detected.

In the list, select .

Click the button in the toolbar. If the short edge is hidden behind the mesh zoom out, rotate the geometry, then click the button again to find the area highlighted in the figure below.

The two edges are located at the boundary of a small face that forms a fold in the geometry. To find where the two short edges originate from switch to the sequence.

Mesh Part 1

For a better overview of all boundaries on the imported mesh open the window.

In the window, under click .

In the toolbar, click and choose .

Click the button in the toolbar.

In the window for , in the list, choose and . Hold down while clicking in the list to select multiple boundaries.

Click the button in the toolbar. If needed, zoom out and rotate the geometry before zooming in on the boundary again.

Click the button in the toolbar.

On the imported mesh Boundaries 4 and 5 are in the same location as the short edges on the generated geometry. These are isolated boundaries on the outside of the surface mesh, and are attached to the mesh only through a single edge. Isolated boundaries such as these are automatically removed during the last step of the geometry creation process, when the solid object is created.

In the following we will delete these boundaries from the imported mesh. First, we join all boundaries to get rid of Boundary 3 that is responsible for the small fold in the final geometry.

Switch to the window.

Join Entities 1

In the toolbar, click .

This adds the operation to the sequence.

In the window for , locate the section.

From the list, choose .

Click .

According to the node displayed under not all selected boundaries could be joined. This is expected since the two isolated boundaries cannot be joined. Instead we will delete these.

Delete Entities 1

In the toolbar, click .

In the window for , in the list, choose and .

Click in the window toolbar.

Right-click and choose .

After the operation completes the window lists only one boundary for the mesh. The isolated boundaries are no longer there, but the small fold in the mesh is still visible.

Close the window.

Geometry 1

In the window, under click .

In the toolbar, click .

Click the button in the toolbar.

Zoom in on the region highlighted in the figure above.

The short edges are no longer present in the geometry. The small fold in the surface has also disappeared because this time it is part of a larger surface, and therefore it could be removed by the mesh simplification algorithm that is part of the conversion to geometry.

Mesh 1

In the window, under right-click and choose .

This time the mesh builds without any warnings.

Geometry 1

Import 1 (imp1)

In the window, under click .

In the window for , locate the section.

In the text field, type 0.008.

By setting a tighter tolerance we are reducing how much the imported mesh can be modified by the mesh simplification algorithm. This tolerance is relative to the entire geometry and together with the , which is relative to the local feature size, controls how much the imported mesh can be modified at a certain location before converting it to geometry. Decreasing the relative simplification tolerance should work in this case, since apart from some small local defects the imported surface mesh seems quite good.

Click .

With the smaller tolerance the processing time increases, but the generated solid object follows the imported mesh more accurately.

Block 1 (blk1)

In the following create a block and combine it with the imported vertebra geometry to create a domain outside of the vertebra, and to cut the geometry in half.

In the toolbar, click .