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See
"Checking the Calibration of the Polaris Vicra System" on page 57
calibration.
Reflections and other IR Sources
Reflections and other IR sources may cause markers to become "lost" in the background IR light.
These reflections and sources should be eliminated or minimised as much as possible. Reflections
occur when IR light from the illuminators is reflected off surfaces such as:
•
drapes - ensure that drapes are placed such the reflections are minimised
•
reflective surfaces - minimise reflective surfaces in the environment
•
tools - design and manufacture tools in non-reflective materials. Refer to the "Polaris Tool
Design Guide" for further information.
Other sources of IR light, such as operating room lights, should be considered when positioning the
system in order to minimise interference from such devices.
What happens if the markers are partially blocked from the view of the Position
Sensor?
The Polaris Vicra System requires a clear line-of-sight to the markers. Anything that interferes with
the line-of-sight can reduce the measurement accuracy. The magnitude of the errors that are caused
by partial occlusion of the markers depends on the number of markers, the geometry of the tool, and
the severity of the occlusion. Errors caused by partial occlusion can have exactly the same
magnitude for active and passive tools. However, there is more opportunity to partially occlude the
passive markers because they are larger than active markers.When designing a new tool, it is
important to consider the effect of partial occlusion on its accuracy. The values used for these
parameters will also depend on the design of the tool. The best value is usually determined through
experimentation. See the "Polaris Tool Design Guide" for further information on tool design.
Why is the tool reported as missing?
A tool may be reported as missing if:
•
it has been rotated so that too few markers are visible to the Position Sensor
•
the tool is no longer in the field of view
•
the tool is damaged, for instance if it is bent
•
the condition of the makers has deteriorated, for instance scuffed, or occluded with foreign
matter.
The Position Sensor seems too warm
The Position Sensor will be warm to the touch during normal use. If the temperature goes out of
range an error message will be shown in NDI ToolBox application software.
Polaris Vicra User Guide - Revision 2
Troubleshooting
for more details about
75
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