Example: Missing Tracking Marker in Static Trial

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The following example is contrived, but it does happen. Consider the following right thigh segment constructed using static markers RPPT, RAPT, RPDT, RADT

missingStaticMarker1.jpg

These tracking markers are saved to a model template, but for the next subject the static trial is missing the RAPT marker

missingStaticMarker2.jpg

If the model template is applied to this trial, the right thigh segment cannot be built.

The obvious solution to this problem is to simply remove the RAPT marker as a tracking marker, but there may be an occasion where one of the remaining 3 markers is missing for much of the movement trials because of occlusion. The solution is to replace the missing tracking target with a landmark that is placed at the expected location.

missingStaticMarker3.jpg

Create a new hybrid model with one of the movement trials. Select one frame of the movement trial in which the four markers exist. (e.g. set the calibration range). Create the landmark using the 3 tracking markers that are in the static trial, and set the offset to be the missing marker. When you select the apply button, the values for the ML, AP, and AXIAL edit boxes are populated automatically as shown below.

missingStaticMarker4.jpg

Now, click the check box to use these offsets instead of the RAPT marker. Save this model template to disk.

missingStaticMarker5.jpg

Switch to the hybrid marker with the missing tracking marker. Apply the temporary model template, and the landmark will appear where it is expected.

missingStaticMarker6.jpg

The original template should then be APPENDED to this model. Note that if the model template is applied, the landmark will disappear. You will need to re-select the RAPT landmark because Visual3D will have lost the marker because it cannot find it.

missingStaticMarker8.jpg

When the model is applied to the walking trials Visual3D will first look for a TARGET with the name RAPT (it will not look for a LANDMARK first). When it finds the TARGET it will simply use it.

missingStaticMarker7.jpg

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