User guide

Charnwood Dynamics Ltd. Coda cx1 User Guide – Advanced Topics III - 1
CX1 USER GUIDE - COMPLETE.doc 26/04/04 97/162
(ii) Any component virtual markers must themselves be valid.
If any of these conditions are violated the virtual marker definition is rendered invalid.
Anyone contemplating the analysis described in section 5 will be aware of the need to
avoid division by zero in the solution of weights. This only arises if the context frame
markers, M
1
, M
2
and M
3
, are co-linear during the static acquisition - contrary to the
placement advice given above. Should they subsequently stray into co-linearity during
dynamic acquisition the error will be picked up as previously described.
Having successfully defined some Virtual Markers . . .
Once defined, Virtual Marker Position appears as a new data type in the graph Add Plot
dialogue, if the component markers (and their components) are available in the current
data file.
Valid Virtual Markers may be used in stick-figure joins – they are automatically added to
the marker lists in the Stick Figure Joins Setup dialogue. They are added before the real
markers in the lists, with negative index numbers (so the lists must be scrolled upward to
see them).
Likewise they may be used in the definition of Vector Angles (see Using Vector Angles).
Virtual Marker defintions are saved with the Setup (Setup: Save Setup…) but it is
important to bear in mind that they are internally referred to by number, rather than by
name. Deleting a virtual marker is liable to upset any scheme saved with a setup,
especially if the deleted item is itself a component for a ‘compound’ virtual marker.