Northern Digital Polaris Vicra User Manual page 45

How the Polaris Vicra System Works
transformation. If fewer markers than the minimum number of markers are used in the calculations,
then the tool will be reported as MISSING.
For example, consider a four-marker tool that has three markers inside the characterized
measurement volume, and one marker outside of the characterized measurement volume. If the
minimum number of markers parameter is set to 3, the Polaris Vicra System will report
transformations for the tool (as long as the other tool tracking parameters are satisfied). If the
minimum number of markers parameter is set to 4, the Polaris Vicra System will report the tool as
MISSING.
Note
You can tell the Polaris Vicra System to report the positions of tools that have less than the minimum number of
markers inside the characterized measurement volume by using reply option 0x0800 with the TX or BX command.
This may reduce the accuracy of the transformations. See the "Polaris Application Program Interface Guide" for
details.
Minimum Spread
The minimum spread parameters specify the minimum size 3D box that must contain all the
markers used in the calculation of a tool transformation. The length, width, and height of this box
must be greater than the specified Minimum Spread 1, Minimum Spread 2 and Minimum Spread 3
parameters, respectively, or else the system will not return a transformation.
This setting is optional. For more details on the minimum spread parameter, see the "Polaris Tool
Design Guide".
Polaris Vicra User Guide - Revision 2 33