Method for determining a start offset between a video recording device and an inertial measurement unit for use in synchronizing motion data of an object collected by the inertial measurement unit attached to the object with video frames captured by an image sensor of the video recording device of the object in motion
A method is provided for determining a start offset between a video recording device and an inertial measurement unit (IMU) for use in synchronizing motion data of an object collected by the IMU attached to the object with video frames captured by an image sensor of the video recording device of the object in motion. The start offset is then used to synchronize subsequently captured video frames to subsequently collected IMU motion data.
1. A method of determining a start offset between a video recording device and an inertial measurement unit (IMU) for use in synchronizing motion data of an object collected by the IMU attached to the object with video frames captured by an image sensor of the video recording device of the object in motion, wherein the image sensor of the video recording device has a field of view and an “on” state for video frame collection, and the IMU includes a light source and a calibration state that initiates a predetermined sequence of timed “on” and “off’ states for the light source, the method comprising: (a) placing the image sensor of the video recording device and the IMU in a dark environment and positioning the light source of the IMU within the field of view of the video recording device; (b) generating a start command in a remote control device, wherein the start command includes one or more start signals; (c) the IMU receiving one of the start signals, thereby causing the IMU to initiate the predetermined sequence of timed “on” and “off’ states; (d) the video recording device receiving one of the start signals, thereby causing the video recording device to be switched to the “on” state for video frame collection; (e) performing a black/non-black analysis of the video frames collected by the video recording device, wherein the video frames are black when the light source is “off’ and the video frames are non-black when the light source is “on”; (f) initiating a calibration stop time event; and (g) determining the start offset between the video recording device and the IMU based on: (i) the number of time intervals that the IMU ran for up until the calibration stop time event, (ii) the total number of black and non-black video frames up until the calibration stop time event, and (iii) the predetermined sequence of timed “on” and “off’ states, wherein the start offset is used to synchronize subsequently captured video frames to subsequently collected IMU motion data.
2. The method of claim 1 wherein the start command includes two separate start signals, one for receipt by the IMU, thereby causing the IMU to initiate the predetermined sequence of timed “on” and “off” states, and the other for receipt by the video recording device, thereby causing the video recording device to be switched to the “on” state for video frame collection.
3. The method of claim 1 wherein the start command includes only one start signal for receipt by both the IMU and the video recording device, thereby causing the IMU to initiate the predetermined sequence of timed “on” and “off” states, and also causing the video recording device to be switched to the “on” state for video frame collection.
4. The method of claim 1 wherein the remote control device is further configured to generate a stop command, and wherein the calibration stop time event occurs upon detection by the IMU of a stop command by the remote control device.
5. The method of claim 1 wherein the video recording device is a camera of a mobile device.
6. The method of claim 1 wherein the video recording device is a camera.