Example f611: Describing the process of obtaining a simple mesh

This example explains the process of creating a 3D mesh from the cast of a generic bladder.

A plaster cast in the shape of a generic bladder was created by replicating an anatomically accurate physical model of a male bladder. A mesh was then drawn on the cast and node points obtained using the faro arm, a device for obtaining the 3D position of points on an object. Using the Faro arm is described in Example 21d. Linear elements were then created on the surface of the bladder using the cmgui element creator, which can be found in the viewers menu of the CMGUI command window.

Derivatives were then added to the initial bilinear mesh. The 'update node hermite' command can be used for this (see example 125 for the implementation of this command). The command converts the bilinear mesh to a bicubic linear mesh.

Geometric data points of the bladder surface were then obtained using the hand held Polhemus 3D digitiser. The mesh was then fitted to these data points to get the correct information for the derivatives. There are many examples of fitting geometric data. Some nodes such as the ones outlining the entrance of the ureters to the bladder were fixed during the fitting process because the fit would not be able to describe these accurately due to the lack of information at the points around the ureters.

Once the fit of the bulk of the mesh was complete, the nodes surrounding the ureters required manual editing to obtain the required shape. Example at describes the process of manually editing the nodal derivatives in CMGUI.

The thickness of the bladder is accounted for by extruding the surface mesh to create 3D elements. The new nodes created maintained the derivatives from the corresponding outer nodes. The nodes were projected inward towards the centre of the mesh nodes by a distance equal to the thickness. The new node and element files were written out, they then could be read into the backend of CMISS (after reading in the correct basis functions).

The prostate, external sphincter, internal sphincter and ureters were added to the mesh. They were created from physical models showing the organs and their relationship to the bladder.

Running this example simply read in the node and element files and describes the use of versions.


Files used by this example are:

Name                    Modified     Size

3D_cartesian.ipcoor 09-Feb-2001 572 blad_ref.ipbase 09-Feb-2001 8.3k blad_ref.ipelem 09-Feb-2001 122k blad_ref.ipnode 09-Feb-2001 363k bladder_minimal.ippara 12-Nov-2002 5.9k example_f11.com 09-Feb-2001 1.1k

Download the entire example:

Name                           Modified     Size

examples_f_f6_f61_f611.tar.gz 19-Aug-2006 123k

Graphical output from this problem is given here.


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Input last modified: Tue Nov 12 12:52:20 2002


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