Pitch and roll from acceleration

Pitch and roll estimation from triaxial accelerometer data. This is a non-iterative estimator with |pitch| constrained to <= 90 degrees. The pitch and roll estimates give the least-square-norm error between A and the A-vector that would be measured at the estimated pitch and roll. If A is in the animal frame, the resulting pitch and roll define the orientation of the animal with respect to its navigation frame. If A is in the tag frame, the pitch and roll will define the tag orientation with respect to its navigation frame.

Usage

a2pr(A, sampling_rate = NULL, fc = NULL)

Arguments

A

An nx3 acceleration matrix with columns [ax ay az] or acceleration sensor list (e.g., from readtag.R). Acceleration can be in any consistent unit, e.g., g or m/s^2.

sampling_rate

(optional) The sampling rate of the sensor data in Hz (samples per second). This is only needed if filtering is required. If A is a sensor data list, sampling_rate is obtained from its metadata (A$sampling_rate).

fc

(optional) The cut-off frequency of a low-pass filter to apply to A before computing pitch and roll. The filter cut-off frequency is in Hertz. The filter length is 4*sampling_rate/fc. Filtering adds no group delay. If fc is not specified, no filtering is performed.

Value

A list with 2 elements:

• p: The pitch estimate in radians

• r: The roll estimate in radians

Note

Output sampling rate is the same as the input sampling rate.

Frame: This function assumes a [north,east,up] navigation frame and a [forward,right,up] local frame. In these frames, a positive pitch angle is an anti-clockwise rotation around the y-axis. A positive roll angle is a clockwise rotation around the x-axis. A descending animal will have a negative pitch angle while an animal rolled with its right side up will have a positive roll angle.

See also

m2h

Examples

samplematrix <- matrix(c(0.77, -0.6, -0.22, 0.45, -0.32, 0.99, 0.2, -0.56, 0.5),
  byrow = TRUE, nrow = 3
)
list <- a2pr(samplematrix)