animalTrack (version 1.0.0)

roll: Calculate roll angle.

Description

calculate roll angle using measurements from a three-axis accelerometer. However, only two axes are required.

Usage

roll(y, z)

Arguments

y

a numeric vector of y-axis values.

z

a numeric vector of z-axis values.

Value

$-\pi \le$ roll $\le \pi$

Details

Roll angle is the angle between the left-right axis and the horizon. The angle is calculated assuming the NED (north, east, down) frame of reference, where x is north, y is east, and z is down. Typically, this is measured with an accelerometer and is scaled from -1 to +1. Using NED, this means that when the accelerometer is measuring 1g, this is equal to -9.8 $m/s^2$. This also means that if the axis is aligned with the earth gravity vector (i.e. down, towards the center of the earth), it should have a value of +1. Roll angle is calcualted by

$roll = atan2(y,z)$

A downward movement of the y-axis gives a positive roll angle.

References

Ozyagcilar, T. (2012), Implementing a tilt-compensated eCompass using accelerometer and magnetometer sensors. Freescale semiconductor, AN 4248, Rev. 3.

Smith, K. J. (1998), Essentials of Trigonometry. Pacific Grove, CA: Brooks/Cole.

Examples

## Import the yaw, pitch and roll simulated calibration dataset. For
## an explanation of the data use help(yprsim).
data(yprsim)

## Assign accelerometer variables
ay <- yprsim$ay
az <- yprsim$az

## Calculate roll
theta <- roll(ay, az)

plot(theta*(180/pi),type='l',lty=1,lwd=2,xlab="time (s)",ylab="pitch (degrees)",
     main="Roll Calculation (2 roll rotations)")
abline(v=c(126,252),lty=3,lwd=2)
legend(-10,110,legend=c("Roll","Change in \n Rotation"),
       col=c("black","black"),lty=c(1,3),bty="n")
text(50,-70,"Yaw");text(175,-70,"Pitch");text(320,-70,"Roll")