6.6. Building surface

To set the surface options, click on the arrow on the right side of the Create surface for current structure button and select the Surface creation parameters.... The dialog box shown in Fig. 6.16 will be displayed.

• The smoothness of the surface is defined by the Smoothing pass count parameter. With this parameter set at zero value, the form of the surface is as close as possible to the structure. With an increase in the value, the surface roughness disappears.

• If the Interpolate vertex positions box is checked (checked by default), the surface is smoothed at the border of the volume.

• To create the surface only for the largest structure, check the Remove secondary volumes box.

• To fill the cavities and hollows, check the Fill cavities. box. As an alternative, you can use the Fill tool (see Section 3.8.7).

• To fill small cavities, check the Perform morphological closing box. As an alternative, you can use the Remove holes (closing) tool (see Section 3.8.7). The volume of the model is first increased and then decreased by the operation radius provided (in millimeters or voxels). The shape of the surface and the external dimensions are not changed.

• To eliminate visual surface defects, check the Perform morphological opening box. As an alternative, you can use the Remove noise (opening) tool (see Section 3.8.7). The volume of the model is first decreased and then increased by the operation radius provided (in millimeters or voxels). The shape of the surface and the external dimensions are not changed.

• If the Apply current clipping box box is checked, then the surface is built only for that part of the structure which is inside the cube.

To apply the settings, click OK. To cancel, click Cancel.

When the segmentation project is saved, all the surface building parameters are saved in the file. For details on saving projects, see Section 6.11.

To build a surface without setting the parameters first, click the button.

The transparency of the polygon model corresponds to the transparency of the segmented structure.

Attention! Polygon model transparency is not supported if:

• a CPU has been chosen as the render device;

• the software was installed on macOS.

To customize the parameters for each of the surfaces built, unfold the mesh properties tree on the segmented structure panel (see Fig. 6.17). Click the Change surface creation parameters button. Customize the surface parameters in the dialog box that pops up (see Fig. 6.16). Click OK to build a surface with the new parameters or Cancel to cancel.

If the Structure visibility box is unchecked for this structure or mesh, you cannot use the cutting tools, as well as the Segmentation from point by mask, Region growing and Vessel tree segmentation tools.

You can only edit hidden meshes with intelligent volume editing tools, such as Grow (dilation), Shrink (erosion), Remove noise (opening), Remove holes (closing) (for details see Section 3.8.7) , as well as with the Union, Subtract, Subtract dilated, and Intersect tools (for details see Section 6.8). In this case, the following message pops up: «The target structure is hidden. Are you sure you want to apply the operation to it?» Click Yes to proceed or No to cancel.

The surface is represented by a polygon model made of triangles.

The program automatically determines the maximum possible number of triangles required for creating a surface imitating the volume surface. The number of the triangles making up the surface may be changed on the Segmented structure panel.

To change the number of the triangles making up the surface, unfold the mesh properties tree on the Segmented structure panel (Figure 6.17).

Double-click with the left mouse button on the value in the Triangles field. Change the value showing the number of triangles and press Enter key on the keyboard.

If the number of triangles entered is too small or too large to build a surface, the DICOM Viewer will use the value from the permitted range which is the closest to the value provided by the user.

If the entered value equals 0, the program will build a surface using the maximum possible number of triangles which will be shown in the Triangles field.