R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 169
prototyping systems. The STL fi le format is more fully described in Section
4.6. However, before the data could be used to produce a model, gaps in
the data, such as the area at the eyebrows, were fi lled. This was achieved
by using surface creation software to create a patch that continues the shape
of the captured data surface. The patch was created to follow the natural
curves of the surrounding data and replicate the surface as well as possible.
This required a certain amount of judgement on the part of the operator.
However, this case did not present great diffi culty in this respect, as the
missing areas were relatively small.
The fi le size was reduced at this stage by removing unnecessary points.
This was achieved without sacrifi cing accuracy because there were a vast
number of points in the captured data coupled with the fact that the accuracy
of the scan data is greater than can be achieved by subsequent RP
processes. An offset surface was created from the captured data and the
gap between them closed to create a fi nite bound volume. To minimise fi le
size and model cost, only the specifi c area of interest was selected. The
resulting data was stored as an STL fi le. The STL fi le size was reduced to
3.6 MB. This was then laterally inverted (‘mirrored’) as shown in Fig. 6.43.
In this case, the process of creating a valid STL fi le from the scan data took
approximately three hours, but this will vary from case to case. The model
in this case was produced using Laminated Object Manufacturing (LOM TM )
– see Section 5.8 (8). The model is shown in Fig. 6.44. The scan data and
STL fi le were archived, in case it is necessary to reproduce the model or
for future reference.
Prosthesis manufacture
This case involved the manufacture of an osseointegrated implant retained
silicone prosthetic of the left eye (see medical explanatory note 8.2.1 for an
6.43 STL fi le and ‘mirrored’ fi le of the unaffected eye.