// The variances: Add the 2D and 3D standard deviations.
// If the user doesn't provide them, we choose the following:
// 2D (detector) variance: Assuming the detector has a standard deviation of 3 pixels, and the face size (IED) is around 80px. That's 3.75% of the IED.
// 2D (detector) variance: Assuming the detector has a standard deviation of 3 pixels, and the face size (IED) is around 80px. That's 3.75% of the IED. Note: Maybe this should even be in pixel, so 4 instead of 0.04.
// 3D (model) variance: 0.0f. It only makes sense to set it to something when we have a different variance for different vertices.