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Developer Kit for the PrioVR - Full-body immersion to interact naturally with virtual worlds. Read more

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Developer Kit for the PrioVR - Full-body immersion to interact naturally with virtual worlds.

STEM, Inverse Kinematics, and Accuracy

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This update addresses questions we've been receiving regarding this weekend's STEM update and video from Sixense.

The STEM update video from update #13 on Oct. 4 2013 clearly illustrates the difficulty of 1:1 motion tracking using the standard STEM configuration consisting of a single base station and only 5 trackers. In short, the problem is that with so few trackers, Inverse Kinematics (IK) must be used to calculate a best-guess pose for the player. Thus, rather than having an accurate in-game pose that is identical to the pose of the real-world player, you are getting a calculated guess of the pose of the real-world player. With the limit of only 5 trackers imposed by the standard STEM configuration, these errors will always remain.

Below are several screen-shots from the STEM update video that clearly illustrate the IK problem:

Figure 1 – ( Stem update #13 1m23s) - Notice above that the left arm angle is incorrectly calculated and the legs in the in-game avatar are impossibly overlapped.
Figure 1 – ( Stem update #13 1m23s) - Notice above that the left arm angle is incorrectly calculated and the legs in the in-game avatar are impossibly overlapped.
Figure 2 – (Stem update #13 1m25s) - Notice above that  the right arm and left leg are incorrectly calculated in a quite dramatic way.  Additionally, the left arm is more subtly incorrect.
Figure 2 – (Stem update #13 1m25s) - Notice above that the right arm and left leg are incorrectly calculated in a quite dramatic way. Additionally, the left arm is more subtly incorrect.
Figure 3 – (Stem update #13 1m31s) - Notice above that  the right arm pose is incorrectly calculated in such a way that the arm protrudes through the body.  Additionally, the hip position is are incorrectly estimated.
Figure 3 – (Stem update #13 1m31s) - Notice above that the right arm pose is incorrectly calculated in such a way that the arm protrudes through the body. Additionally, the hip position is are incorrectly estimated.
Figure 4 – (Stem update #13 1m50s) - Notice above that the the pose of both arms is incorrectly calculated as is the hip position and left leg.
Figure 4 – (Stem update #13 1m50s) - Notice above that the the pose of both arms is incorrectly calculated as is the hip position and left leg.
Figure 5 – (Stem update #13 2m00s) - Notice above that the the pose of both arms is incorrectly calculated and the right leg is dramatically mis-calculated.
Figure 5 – (Stem update #13 2m00s) - Notice above that the the pose of both arms is incorrectly calculated and the right leg is dramatically mis-calculated.
Figure 6 – (Stem update #13 2m06s) - Notice above that the the pose of both arms is dramatically incorrect.  The hip position and right leg are also mis-calculated.
Figure 6 – (Stem update #13 2m06s) - Notice above that the the pose of both arms is dramatically incorrect. The hip position and right leg are also mis-calculated.
Figure 7 – (Stem update #13 4m24s) – Here the player literally runs into the wall, a common complaint that seems specific to the PrioVR system.
Figure 7 – (Stem update #13 4m24s) – Here the player literally runs into the wall, a common complaint that seems specific to the PrioVR system.
Andrew Murray, Brian Parker, and 3 more people like this update.

Comments

    1. Creator Nadim Alam on October 8, 2013

      Good examples, however that was always going to be the case.With a limit of only 5 trackers we knew that was going to happen. Actually even when using kinect i run into similar issues. Yes i understand having 17 sensors like the PrioVR will eliminate all or at least most of this but the problem is the support of having developers accomdate there games for this. As we know with the Stem it will already be compatible with hundreds of games when it releases especially since its backward compatible with hydra games. Above all else, most companies are backing and adding stem system support already in there future games which is what makes it feasible for users to back and purchase.

    2. Creator Sven H. on October 8, 2013

      While this update helps to cover most points that people had on reddit about positional drift and while it shows the weaknesses of the STEM system, I believe a comparison video would be more appropriate. Could you try to recreate the movements using your system?

    3. Creator Jef Mendoza on October 7, 2013

      You actually mean "STEM system" at the end of the statement below, correct?

      "Figure 7 – (Stem update #13 4m24s) – Here the player literally runs into the wall, a common complaint that seems specific to the PrioVR system."

    4. Creator Earth_Pony on October 7, 2013

      Great comparison, thanks! I actually loved STEM's demonstration, it really helped us to see how cool full body integration will be in games! PrioVR is the logical next step, the concept of body tracking done correctly. ^_^