Smoothing 6DOF data

It is possible to smooth 6DOF data in QTM. The smoothing can be applied both in real time and in a capture. Smoothing of 6DOF data can be useful if you need to stabilize noisy data. The smoothing is applied to both position and orientation.

The smoothing algorithm includes two types of smoothing. The first type is "Holt-Winters" double exponential smoothing, taking into account the trend of the data. The second type is a jitter reduction filter, operating within a specified radius. In addition, there is a prediction parameter that can be used to project the trend ahead to compensate for lag. The parameters are:

  • Data smoothing factor of the double exponential filter s, with a value between 0 and 1.
  • Trend smoothing factor of the double exponential filter c, with a value between 0 and 1.
  • Prediction parameter p, corresponding to the number of frames the trend is projected ahead.
  • Position jitter radius rp in mm.
  • Orientation jitter radius ro in degrees.

A disadvantage of smoothing is that it may introduce side effects. Smoothing and jitter reduction may introduce lag, whereas trend compensation may lead to overcompensation or overshoot. The smoothing effect of the filter, including the side effects may depend on the characteristics of the movement, as well as the capture rate. This should be taken into account when choosing the smoothing parameters.

QTM includes presets with useful combinations of smoothing parameters for various situations. The presets can be selected individually per rigid body. The available filter presets are:

  • No filter
    No smoothing. This is the default option.

  • Multi-purpose
    Light smoothing and jitter reduction. This preset is suitable for most situations which require effective smoothing of light noise, while keeping side effects to a minimum. The filter parameters are: s=0.25, c=0.25, p=0, rp=5, ro=5.

  • High stability
    Strong smoothing and jitter reduction. This preset is suitable when you need stable data in challenging tracking situations. In case of high accelerations or impacts filtering may lead to noticeable side effects. The filter parameters are: s=0.5, c=0.5, p=1, rp=25, ro=25.

  • Static pose
    Effective jitter reduction for immobile objects. Application of this preset to moving rigid bodies may lead to noticeable lag for small displacements and rotations within the specified radius. The filter parameters are: s=0, c=0, p=0, rp=10, ro=10.

The selected presets in the rigid body definitions in the Project Options will be applied in real time and in subsequent captures when Calculate 6DOF is checked in the Processing options. It is also possible to reprocess captures with different presets.

The effect of the smoothing filter can be visually inspected in the 3D view window by comparing the markers of the rigid body overlay in the 3D view window with the measured marker positions. For more detailed comparison of the 6DOF data, you can define the same rigid body twice, one with filter and the other one without.