OptiTrack Techniques


This video covering new features in Motive v2.1 moves along at a rapid pace which might be a bit confusing to new users as it was designed for people already familiar with the Motive workflow.  I’m opening with it here as it can be helpful in raising awareness of what may be different in the working methods and interface design in our version of Motive from that shown in videos based upon earlier versions of the software.  Those early foundational videos are still useful, however it is important to understand that some of the things being shown may have changed in the new and improved Motive 2.1 package.

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The Mocap PC in E58 is rack mounted and intended to stay powered on 24/7 to allow IT to manage it remotely via the School of Film/Video network. If for some reason you find it is off you can power it up with the flush button located on the face panel.

Our dozen OptiTrack Flex13 cameras are powered by a set of three OptiHub2’s mounted on the truss supporting the cameras. The cameras will power on when the the Motive software is launched.  The cameras may be used upon powering up, however the will be more accurate once they have warmed up to their normal operating temperature.

“The cameras will heat up with extended use, and changes in internal hardware temperature may also affect the capture data. For this reason, avoid capturing or calibrating right after powering the system if possible. Tests have found that for optimal accuracy the cameras need to be warmed up in Live mode for about an hour until they reach a stable temperature.”

Once you have logged out of Motive, the cameras will power down, however the hubs will remain powered.

Before leaving E58 Please be sure that the projection screen is retracted so that the surface is protected, and that the projector is powered off in order to preserve bulb life.

The door to E58 does not always latch when it swings closed, so after leaving the room please pull on the door knob to be certain that it is actually latched.

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build-10158When you log into the mocap computer in E58 you are logging into your School of Film/Video account.

Following are the procedures that were recommended for the Spring 2019 course. They may change for the Spring 2020 course so please check with John Brennan and/or Michael McNeff on the current procedures.

You can save and load files to your account by clicking on the File Explorer icon located on the left side of the taskbar at the bottom of the monitor screen, then clicking FVCentral (F:) which opens to a set of file folders. You can click on Students which will open up a list of student names. You then scroll to your name and click on it to open your file folders. The path shown in the address bar could be something like:

> ThisPC > FVCentral(F:) > Students > Your_Name > Depositbox

You can also save and load files by using the class folder located in my FVCentral account:

> ThisPC > FVCentral(F:) > Faculty_Staff > Michael_Scroggins > Courses > Motion_Capture_for_Artists_2019

or create a folder in:

> ThisPC > FVCentral(F:) > Faculty_Staff > Michael_Scroggins > Public >

Another option is to hook up a personal storage device to the computer such as a portable hard drive (formatted as ExFat or Fat32) or a flash drive, then save and load files using that device. On the front panel of the computer there are two USB Type C connectors just to the left of the USB Type A connectors typically in use for the mouse and keyboard.

DO NOT SAVE FILES TO THE E58 COMPUTER AS THEY WILL BE ERASED WHEN YOU LOG OUT OF YOUR ACCOUNT!

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Motive_FirstLaunch_21

We are using OptiTrack’s Motive:Body software which as its name implies is designed for capturing human performance.  The OptiTrack Documentation Wiki contains instructions on operating the system.  It is possible to read through the linked documentation in whatever structure serves your needs as a user. There are also user forums providing discussion and support.

An obvious place to start is the Quick Start Guide.

Saving and loading files:

 

Plugins 


Precision Capture Calibration Tips:

  • Wand slowly. Waving the wand around quickly at high exposure settings will blur the markers and distort the centroid calculations, at last, reducing the quality of your calibration.
  • Avoid occluding any of the calibration markers while wanding. Occluding markers will reduce the quality of the calibration.
  • A variety of unique samples is needed to achieve a good calibration. Wand in a three-dimensional volume, wave the wand in a variety of orientations and throughout the volume.
  • Extra wanding in the target area you wish to capture will improve the tracking in the target region.
  • Wanding the edges of the volume helps improve the lens distortion calculations. This may cause Motive to report a slightly worse overall calibration report, but will provide better quality calibration.
  • Starting/stopping the calibration process with the wand in the volume may help avoid getting rough samples outside your volume when entering and leaving.

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IMG_20190304_141703E58 as it was set up back in 2019.   Visiting Artist John Brennan is explaining best practices in marker placement based upon a working knowledge of human bone and joint structures –and methods for adapting that understanding to the specific simplifications required for  motion capture.

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These diagrams taken from the Motive 2.1 documentation show the Baseline markerset of 37 markers which serves as a minimum (Click on a diagram to view a larger image).

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Typically we use the Baseline +13 additional markers (50) in order to obtain a higher fidelity capture.

“Asymmetry is the key to avoiding the congruency for tracking multiple markersets. When there are more than one similar marker arrangements in the volume, marker labels may be confused. Thus, it is beneficial to place segment makers — joint markers must always be placed on anatomical landmarks — in asymmetrical positions for similar rigid bodies and skeletal segments. This provides a clear distinction between two similar arrangements. Furthermore, avoid placing markers in a symmetrical shape within the segment as well. For example, a perfect square marker arrangement will have ambiguous orientation and frequent mislabels may occur throughout the capture. Instead, follow the rule of thumb of placing the less critical markers in asymmetrical arrangement.”

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