Dual Depth Sensor Calibration using Flashlight

Revision as of 21:19, 10 October 2013

Introduction

Starting from version 2.4.1.156, iPi Mocap Studio supports new approach to calibration of multiple depth sensors system. Now you can use flashlight or other small glowing marker to perform calibration for depth sensors. This new calibration procedure is very similar to one used for Multiple_PlayStation Eye Cameras Configuration. But in case of depth sensors the overall workflow is simpler:

• There is no need to touch floor by flashlight during recording.
• No marking of points as ground in iPi Mocap Studio.

  (depth data is used to detect ground plane automatically)

• No manual adjustments of scene scale in iPi Mocap Studio.

  (depth data is used to determine scale automatically)

Please note that for dual depth sensor configuration you can still use calibration based on 3D plane.

How to Use

Glowing Marker

Mini Maglite flashlight is recommended for calibration. This is a very common flashlight in US and many other countries. Removing flashlight reflector converts it into an ideal glowing marker easily detectable by motion capture software.

If you cannot get a Mini Maglite, you can use some other similar flashlight.

Depth Sensors Setup

You can use both configurations:

• Angle between sensors is between 60 and 90 degrees.
• Angle between sensors in near to 180 degrees that means that sensors are placed opposite to each other.

Recording

• Run iPi Recorder.
• Color stream should be recorded along with depth data. That's why only modes "(depth+color)" can be used.

• Avoid bright lightening and white objects on background during recording of calibration video.
• Start recording.
• Move the marker slowly through your entire capture volume (front-top-right-bottom-left-back-top-right-bottom-left). Start from top and move the marker in a descending spiral motion.

Tip. The exact trajectory of the marker is not so important, just try to cover the whole capture volume, or at least its perimeter.

Tip. You should make the marker visible to both depth sensors at all times. Hold the marker in the straight arm away from your body.

Processing

• Open recorded calibration video in iPi Mocap Studio.
• Choose Calibration project type in New Project Wizard.
• Adjust Region-of-Interest so that glowing marker is visible at the beginning and at the end.
• Click Calibrate Based on Flashlight Marker button.
• Wait while automatic calibration is performing.
• Check resulted statistics:
  • Good Frames Count should be at least 100 (500 and higher are recommended values).
  • Average Position Error (meters) should be less than 0.100 (0.050 and lower are recommended values).

• Save results using Save scene... button on Scene tab.

When to Use

• For Triple Depth Sensor configuration.

• When flat rectangular veneer/plywood/cardboard/pasteboard/foamboard of required size is not available.
• In some cases calibration based on flashlight marker produces more precise results in comparison with 3d plane based calibration.