Figure 6
From: Reconstruction of the respiratory signal through ECG and wrist accelerometer data
Acceleration recording at the wrist. The photo shows the placement of the SOMNOwatch plus device (Somnomedics GmbH, Randersacker, Germany) at the wrist with the coordinate axes (x, y, and z; yellow) according to the device’s orientation as well as the gravity acceleration vector (red) pointing vertically upwards from the center of the earth. The device measures the three components of the gravity acceleration with respect to its coordinate axes. From this data the two orientational angles, \(\vartheta \) = angle between x axis and gravity acceleration and \(\varphi \) = angle between y axis and projection of the gravity acceleration into the \(y-z\) plane (dashed red vector), can be calculated according to Eq. (3).
