This example covers: This example links to the following examples which also contain relevant information: The process described below is that used by the NERF-funded musculoskeletal modelling project currently being undertaken in the Bioengineering Institute for production of volume meshes for the irregular bones of the human body.

Created by: Steven Thrupp 27 Aug 2002

Creating an initial mesh: using the Faro Arm

The initial linear Lagrange mesh used in this process was created using our Faro Arm. The process of using the Faro Arm in constructing an initial mesh is described in example 21d.

Obtaining Data for Fitting: Model Maker 4

While use of the HLS (Hand Held Laser Scanner) is described in example 21d, this example gives a brief description of our other laser scanner, Model Maker 4 (and a pointer to more extensive documentation for its use and calibration). Model Maker 4 is a Faro Arm-mounted laser scanner. As such it has a number of advantages over the HLS:

Figure 1: Faro-mounted laser scanner

In order to use the Laser scanner, or if using it for the first time after a period of disuse, there are two processes the user should go through first. First, you should ensure that the Faro Arm itself is calibrated and second, ensure that the laser scanner is correctly aligned with the Faro-Arm. This is a slightly time-consuming process however it is essential to ensure that these two things are correct otherwise one will run into difficulty down the line when trying to align your data within the Model Maker package.

Faro Arm Calibration

Calibrating the Faro arm is straightforward. It is described in example 21d however is described here again on the Windows 2000 OS. Program Menu >> Faro >> Caliper 3D. Within Caliper 3D go Settings >> Probes. Within This dialogue boss select either Point Probe or Ball Probe. If Ball probe you will need to specify the diameter. (If point probe no diameter is necessary.) Then look in the Calibration box within the current dialogue box and go 1"Ball. Depressing this button will provide you with a new dialogue box. From this point on you are required to obtain 27 points by clicking on the 1"Ball magnetically connected to the base of the Faro Arm. The points should be obtained in a reasonably uniform fashion (ie, 5 points around the horizontal equator of the ball, then 5 around the vertical, followed by e.g. around the top of the ball etc.). Points are obtained by clicking a front button on the Faro Arm when in position and then clicking a back button in order to accept the the point you have just obtained. The software will count off the number of points you have obtained. When you have obtained these 27 points the software will calculate an RMS for you which will indicate the calibration status.


Sensor Alignment

Once you are confident with the calibration of the Faro Arm the next step is to align the Laser scanner with the Faro Arm. This is done within the Model Maker software package.

FE geometric face-fitting to bone data

Once your data has been acquired you need to align it with your mesh using CMGUI. This process is described in example 21d. Once this is done you need to convert your frontend files to backend files. A script is given in the Notes section below that can be used to convert 8-noded volume elements from the .exelem to .ipelem format (trilinearex2ipelem.pl). Once your files are in this backend format you are ready to use cm to fit the initial linear mesh to the data using tri-cubic Hermite basis functions. The command file and necessary files for this process are given in the example below.

Notes

The following perl scripts are used in various aspects of the above process:

Initial Mesh Fitted Mesh

Results can be view with view.com.