Biomedical Engineering Reference
In-Depth Information
Fig. 7.5
Inner, outer, and assembly parts of the vertebral volume, in point cloud representation
complex shape patches, from the given point clouds. The number of patches
represents a compromise between the fidelity of the original model and the maneu-
verability in simulations of the resulted model. By enclosing the multitude of
patches, a shell structure was built. The tight closed volume can be saved as a solid
model.
The conversions of the point cloud formats to surfaces were made into the
Geomagic Studio environment [
12,
21
] .
The outer point cloud contains an amount of 6,694 points, while the inner point
cloud contains a smaller number of 4,642 points. At this stage, some isolated points
were selectively eliminated from the cloud in order to prevent a surface generation
failure. The selection of the erasable points was made taking into account the native
geometrical imperfections of the vertebra.
During the wrapping process, the two point clouds were transformed apart in two
polygonal shells. The outer volume consists of 13,374 triangular surfaces while the
inner volume consists of 9,284 triangles.
The mesh structures of both objects prove to be very rough after initial wrapping (see
Fig.
7.6
), a refinement of the element size being demanded. To achieve smooth meshes,
the bed triangular elements were first repaired and reduced eight times in size after. The
smooth structures (see Fig.
7.6
) are now ready to be transformed into
shape phase
.
The next stage of surface generation was to replace the fine mesh with larger
patches (NURBS surfaces) in order to generate a more handling object with the
same geometrical characteristics (see Fig.
7.7
).
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