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Each face is assigned a face normal in the tool definition file (described on page 31). The face
normal is a vector pointing in the same direction as the tool face, to let the Polaris Vicra System
know the direction each tool face is facing. The system will track the face most directly oriented to
the Position Sensor (i.e. the face with the smallest angle between the face normal and the sensors in
the Position Sensor). If the minimum number of markers are not visible on the face most directly
oriented to the Position Sensor, the system will attempt to track another face.
The system has a hysteresis of 2° when determining whether to switch faces. The system will
determine the angle between the sensors and each face of the tool. If the face with the smallest angle
is 2° smaller than the current face's angle, the system will switch to the new face.
3.6
Tool Definition File
A tool definition file (formatted as .rom) describes a tool to the Position Sensor. The information
stored in the tool definition file includes the geometry of the tool's markers, the tool's manufacturing
data, information on marker and face normals, groups and faces definitions, and the parameters used
to track tools. For more information on the parameters used to track tools, see Tool Tracking
Parameters below.
A tool definition file must be loaded into the system (by the host computer) before the Polaris Vicra
System can track its associated tool. If the Polaris Vicra System is measuring the positions of stray
markers (described in
loaded in order for the Position Sensor illuminators to emit IR light.
Tool definition files can be created in NDI 6D Architect. The procedure used to create a tool
definition file is called tool characterization. For more information on tool characterization, see the
"Polaris Tool Design Guide" and the "NDI 6D Architect User Guide".
3.7
Tool Tracking Parameters
The following tool tracking parameters are specified in the tool definition file (described on page
31).The flow chart on page 34 describes how the Polaris Vicra System uses the tool tracking
parameters to determine which markers to use to calculate a tool transformation, and when to return
a transformation.
For information on how to change the tool tracking parameters and what values to use, see the
"Polaris Tool Design Guide" and the "NDI 6D Architect User Guide".
Maximum 3D Error
The maximum 3D error parameter specifies the maximum allowable 3D error for each marker on
the tool. The maximum 3D error is the difference between the measured and expected location of a
marker on a tool. The expected location of a marker on a tool is specified in the tool definition file
(described on page 31).
If the 3D error for a particular marker is greater than the specified maximum 3D error value, the data
from that marker will be not be used to determine the tool transformation.
Polaris Vicra User Guide - Revision 2
"Stray Marker Reporting" on page
How the Polaris Vicra System Works
37), at least one tool definition file must be
31
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