Looking for Help Figuring Out Motion Noise in Polhemus Data

[Glenn Fleisig]

We have been experiencing some issues with our Polhemus VIPER8 system and wanted to see if anyone on here might have had similar issues with the same system and any suggestions.

We have a VIPER8 system with a 4-in source, which we are trying to use with six 1.8-mm microsensors. Essentially, we're putting three microsensors in a single, stationary plastic block, while moving a second block (containing an additional 3 sensors) through an arc of 120 degrees at a distance of about 20 cm from the stationary block. The sensors in each block are 1 cm apart.

As part of our data analysis, we're running a validation script which calculates the distance between the sensors on each block. As expected, we see minimal motion between sensors on the stationary block; however, we're seeing 5 mm or more between sensors on the moving block. The block is rigid, and the sensors are securely embedded (i.e., they aren't moving within the block) up to the point of the actual internal sensing element.

We've tried the following, to no avail:
• Removing any apparent metallic distorters
• Repositioning the source to be closer and even underneath the capture area
• Swapping sensor positions
• Making sure sensor cables don't interact with the source
• Removing the center sensor on each block to increase the distance between the remaining sensors to 2 cm
• Decreasing the radius from 20 cm to about 5-10 cm

Any thoughts about why we’re seeing this noise in distance between sensors? Any thoughts had to eliminate or reduce this noise? Thank you in advance.

[Edmund Cramp]

I saw similar circumstances in the early motion capture days when I was setting up 3D data collection systems, these types of data problems were observed in virtually all manufacturers' early 3D data collection systems. Back then most of the problems were resolved by describing the problems to the data collection manufacturers - they had all the internal abilities to detect the causes of the issues that users were seeing ... often because users were seeing problems that the manufacturers had only assumed couldn't exist.
Virtually everything has been resolved by talking to the manufacturers - I've always seen users as classically much better at observing problems, and the manufacturers good at fixing them once they hear about problems that they had never thought could happen - so this is how everything "evolves" to work better.

[Ruhollah Basatnia]

Based on the information provided, it seems that the issue you are experiencing could be due to a number of factors, including electromagnetic interference, sensor placement, or calibration issues.

Electromagnetic interference (EMI) can be a significant source of noise in Polhemus systems. EMI can be caused by a variety of factors, including nearby electrical equipment, metal objects, or even the presence of other Polhemus systems. To reduce the impact of EMI, you can try repositioning the system in a different location, away from potential sources of interference. You may also want to try shielding the system using materials such as copper tape or aluminum foil.

Sensor placement can also be a factor in the accuracy of Polhemus systems. The sensors should be placed as close to the object being tracked as possible and should be securely mounted to the object to prevent any movement. You may want to double-check that the sensors are properly aligned and securely mounted within the plastic block.

Calibration issues could also be contributing to the noise in your data. It may be helpful to double-check that the system is properly calibrated and that the calibration parameters are appropriate for your specific application. You may also want to try recalibrating the system to see if this improves the accuracy of your measurements.

Finally, it may be helpful to consult with Polhemus technical support for additional guidance and troubleshooting tips specific to your system and application. They may be able to provide additional insights or suggest further steps to help resolve the issue.

[Manvendra Singh]

Are you using FTT feature of Viper (toggled on) for your experiment? Sometimes, using distrortion correction itslef could be the source of noise in EM technology based trackers, if environemt is otherwise free from metals. You can try by toglling FTT off first, and on, afterwards to check.