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3
How the Polaris Vicra System Works
3.1
Introduction
This chapter provides details on how the Polaris Vicra System works. The information is not
absolutely necessary in order to use the system, but it can help increase your technical understanding
of the system. For information on how to use the system, refer to
on page
41.
3.2
Information Returned by the Polaris Vicra System
Do not use the Polaris Vicra System for absolute measurements; the system is designed for relative
measurements only. Treating measurements as absolute may result in an incorrect interpretation of results. If
your application involves personal safety, these incorrect interpretations increase the possibility of personal
Warning!
injury.
When the Polaris Vicra System is tracking tools, it returns information about those tools to the host
computer. The system by default returns:
•
the position of each tool's origin, given in mm, in the coordinate system of the Position
Sensor (see
Note
Transformations with respect to a reference tool (described on page 36), and transformations for a probe with a
tool tip offset (described on page 35) are calculated using application software such as NDI ToolBox.
•
the orientation of each tool, given in quaternion format. The quaternion values are rounded
off, so the returned values may not be normalized
•
an error value for each tool transformation. This RMS value, given in mm, is the result of
the least squares minimization between the marker geometry in the tool definition file and
the tool's measured marker positions
•
the status of each tool, indicating whether the tool is out-of-volume, partially out-of-
volume, or missing. It also indicates whether the port handle corresponding to each tool is
enabled and initialized. For more information on port handles, see the "Polaris Application
Program Interface Guide"
•
the frame number corresponding to each tool transformation
•
the system status, which includes some of the system errors described in
and Flags" on page 49
If requested, the system can also return:
•
tracking errors and flags (described in
tracking errors and flags are returned by default.
•
marker status information, such as whether a particular marker was used to calculate a tool
transformation
Polaris Vicra User Guide - Revision 2
"Global Coordinate System" on page
How the Polaris Vicra System Works
"Using the Polaris Vicra System"
26)
"Tracking Errors and Flags" on page
"Tracking Errors
49). (Some
25
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