Measurement Probe Kit Guide

Main page

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Scope

This page provides information and instructions on how to utilize the Probe Measurement Kit.

Overview

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Measurement probe tool utilizes the precise tracking of OptiTrack mocap systems and allows you to measure 3D locations within a capture volume. A probe with an attached rigid body is included with the purchased measurement kit. By looking at the markers on the rigid body, Motive calculates a precise x-y-z location of the probe tip, and it allows you to collect 3D samples in real-time with sub-millimeter accuracy. For the most precise calculation, probe calibration process is required. Once the probe is calibrated, it can be used to sample single points or multiple samples to compute distance or the angle between sampled 3D coordinates.

Measurement kit includes:

• Measurement probe
• Calibration block with 4 slots, with approximately 100 mm spacing between each point.

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  Measurement probe.
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  Calibration block with slots for the probe tip.

Custom Probes For the best accuracy results, we suggest using a probe with the calibration block that we provide. However, when needed, you can also use any markered object with a tip that projects out for measurement. When using a custom probe, please make sure the object is rigid and the distance from each marker to the measurement tip does not change.

Steps

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Calibrated probe in Motive

Step 1: Probe Calibration

1. Open the Builder pane under View tab and click Rigid Bodies.
2. Bring the probe out into the tracking volume and create a rigid body from the markers.
3. Under the Type drop-down menu, select Probe. This will bring up the options for defining a rigid body for the measurement probe.
4. Select the rigid body created in step 2.
5. Place and fit the tip of the probe in one of the slots on the provided calibration block.
6. Note that there will be two steps in the calibration process: refining rigid body definition and calibration of the pivot point. Click Create button to initiate the probe refinement process.
7. Slowly move the probe in a circular pattern while keeping the tip fitted in the slot; making a cone shape overall. Gently rotate the probe to collect additional samples.
8. After the refinement, it will automatically proceed to the next step; the pivot point calibration.
9. Repeat the same movement to collect additional sample data for precisely calculating the location of the pivot or the probe tip.
10. When sufficient samples are collected, the pivot point will be positioned at the tip of the probe and the Mean Tip Error will be displayed. If the probe calibration was unsuccessful, just repeat the calibration again from step 4.
11. Once the probe is calibrated successfully, a probe asset will be displayed over the rigid body in Motive, and live x/y/z position data will be displayed under the Real-time Measurement section in the Measurements pane.

Caution The probe tip MUST remain fitted securely in the slot during the calibration process. Also, do not to press in with the probe since the deformation from compressing could affect the result.

Step 2: Sample Collection

1. Under the Tools tab, open the Measurements pane.
2. Place the probe tip on the point that you wish to collect.
3. Click Take Sample on the Measurement pane.
4. A virtual reconstruction will be created at the point, and the corresponding information will be displayed over the measurement pane. The sampled points will also be saved in the exported onto the project directory.
5. Collecting additional samples will provide distance and angles between collected samples.

Sampling 3D points using the measurement probe.

Set Origin and Set Orientation

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You can also use the probe samples to reorient the coordinate axis of the capture volume. The set origin button will position the coordinate space origin at the tip of the probe. And the set orientation option will reorient the capture space by referencing to three sample points.

Export Samples

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As the samples are collected, their coordinate data gets written into a CSV file (measurement.csv) in the OptiTrack folder in the Documents directory. Each time a sample is collected, a new line will be written in the CSV file with the information on the 3D positions of the collected measurements and the respective RMSE error values. A new header will be created when the take samples are cleared from Motive and a new sample is collected. If the OptiTrack folder doesn't exist in the documents directory, it may fail to output the csv file. Please make sure "OptiTrack" folder is in the documents directory.

Please check the following directory for the measurement.csv file:

• C:\Users\Public\Documents\OptiTrack
• C:\Users\[your.username]\Documents\OptiTrack

Real-time Streaming

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Location of the probe tip can also be streamed into another application in real-time. You can do this by data-streaming the probe rigid body position via NatNet. Once calibrated, the pivot point of the rigid body gets positioned precisely at the tip of the probe. The location of a pivot point is represented by corresponding rigid body x-y-z position, and it can be referenced to find out where the probe tip is located.