Step-by-Step

Range of Motion

Introduction

The "Range of Motion" (or more commonly R.O.M.) stage connects the markers, the template skeleton, and the actual subject being capture together. In this sense we are using the markers and a skeleton template in order to adjust towards the subject's skeleton - this aids the capture of data and provides us with an actual kinematic model. Without the R.O.M. our output would be marker positions (which can still be imported into MotionBuilder, but it is not the prefered step)

Capture the R.O.M.

The second stage in the ROM is to actually capture the position of the markers over a period whereby the subject goes through a series of exercises that covers their own normal "Range Of Motion". The following video shows the approximate sequence and motions that should be followed - the general idea is to move each joint through its natural range of motion

Note: The subject should always start and finish each capture in the T-Pose (especially with the R.O.M.); the T-Pose doesn't need to follow directly into the sequence, or follow directly out, but it should be performed. The T-Pose is essentially with the arms outstretched, and the legs slightly apart.

The T-Pose is useful to provide a clearly defined start and finished point, it is in the same pose as a character (to which we might map later), and it provides the cameras with a clear view of each marker at the start of a trajectory (we cannot map a trajectory backwards).

Range of Motion Video Example
Click Start in order to start the capture

Tip: Try to be smooth and solid in your motions, and do not take too long - there is no need to repeat as long as each step is done properly.

Make sure you keep your arms outstretched, as much as possible, when you are performing other motion that do not involve them; while this is unnatural, it permits the system to see the markers clearly - which is very important as capturing the R.O.M. should be as clean as possible.

If you are doing extreme motions, such as gymnastics or acrobatics, try and increase your R.O.M. to match the type of your planned motions that will be captured.

If the R.O.M. was not good when we review the capture, first determine why (go back over the settings if markers are not showing up etc) and then perform the R.O.M. again.

Initiating the Template

Once we have the capture we want to use for the R.O.M. we can load it into the post-processing section by pressing "Load Into Post"; alternatively we can load it directly from Data Management (by double-clicking the blue circle with the cross through it)

This will load your data into the post-processing model and change the tab to Post-Processing now under the Subjects tab click "Create Vicon Skeleton Template (vst)"

Warning: At this point you may be prompted to save the Threshold (*.vtt) file and the Calibration (*.cp) file. You will need to save both (without them you will not be able to reconstruct your data after IQ has closed) - you can name them after the session (as they will be saved in the session folder), and not the subject as they shouldn't change if you change subjects

Reconstruction

The reconstruction process takes the 2D data frame-by-frame and processes it through triangulation; this should take the data and produce 3D positions for each marker over the length of the capture.

  • Select the Reconstruction tab
  • Click Run
  • Select the 3D Workspace view and once the reconstruction process has completed you will see the markers in the view represented by small grey spheres

Labelling

Once we have the markers in 3D, they do not relate to the template, therefore by labelling each marker as it corresponds to the template we are creating a match - this is only done for the ROM because once we have the subject's skeleton recorded then have this correspondance

  • Select the Labelling tab (this enables us to label the markers, as currently they are not labelled); now scroll through the time-line to see how the markers are visible - under Trajectories Info we need the number of markers for the first frame to match the number of expected markers (for the ViconFullBodyTraining.vst template, we are expecting 45) - scroll through the frames one-by-one (from the beginning) until 45 is presented under Current Field
  • Once you have a full-frame, you need to move the lower boundary marker (in green) to that position so that the system only takes into account the frame starting from the marker; you can also do this by typing the current frame number
  • Under Modes select Sequence
  • Under Rules select Whole
  • Under Labels select the first marker and then in the 3D Workspace you can select the marker that corresponds - see video below

Tip: It is important to label all markers in a single frame, this doesn't necessarily have to be the first frame, but you should not lose too much of the data you have collected. If you are more than approximately 200 frames into a sequence, and you do not have all 45 markers in a single frame, then you would be advised to redo the range of motion again (checking the suit and markers for correct placement, removing ruffles, etc).

Trace Trajectories

We have now labelled the first frame with all the markers present; however in order to determine the full R.O.M. we need to have all the frames in the sequence labelled. In order to do this we need to perform an "Autolabel ROM" based on the first fully labelled frame.

  • Select the Pipeline tab on the right, and the under the Pipeline Control group, select the Autolabel R.O.M. option from the drop-down menu.
  • Make sure the arrow (Red) is beside the Autolabel Range of Motion entry, and press the Play Button at the bottom and it should process the command (a usual failure at this point comes when the first frame isn't labelled with all the markers or the green marker is not shifted correctly to this first frame)

Calibrate Subject

Once all the frames have labelled markers, we need to set the frame which is approximately in a T-pose and then calibrate the subject according to the ROM to produce a skeleton (VSK - Vicon SKeleton) file that can be used for the remaining captures

  • Select the Subjects tab on the right
  • Under Events click on G and then T (this is used to indicate where the T pose is on the time line, and adds a little 'T' symbol to the timeline where the T-pose is in the sequence)
  • Under Calibration click on Calibrate Subject (this adjusts the VSK to match the subject's skeleton)
  • Under Export click on Export Vicon Skeleton (VSK) (this loads the skeleton into the "active objects" under the Capture tab)

Note: Once the subject's skeleton has been created, it is stored in a file under the name created at the beginning. The file is usually exported back to the capture ready for processing, but if it doesn't then you need to press "Export Skeleton".