# compassAngle

Since R2023b

## Description

example

C = compassAngle(orientations) returns the compass angles in the north-east-down (NED) reference frame based on the orientations. Compass angles are counter-clockwise angles from north of the reference frame to the x-directions of the frames defined by orientations. See Compass Angle for more details.

C = compassAngle(orientations,RF) specifies the reference frame as the "NED" (north-east-down) or "ENU" (east-north-up) reference frame.

## Examples

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Define four sets of Euler angles and obtain their corresponding quaternions.

angles = [0 0 0; 10 0 0; 190 0 0; -10 0 0];
quats = quaternion(angles,"eulerd","ZYX","frame");

Obtain the compass angles and convert their units to degrees.

C = 4×1

0
10.0000
190.0000
350.0000

Next, obtain the compass angles assuming the ENU reference frame.

CENU = 4×1

90
80
260
100

## Input Arguments

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Orientations, specified as an N-by-1 vector of quaternion objects or as a 3-by-3-by-N array of rotation matrices. N is the total number of orientations.

Reference frame, specified as "NED" for the north-east-down frame or "ENU" for the east-north-up frame.

Data Types: string | char

## Output Arguments

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Compass angles, in radians, returned as an N-by-3 matrix of scalars in the range [0, 2*pi). N is the total number of orientations.

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### Compass Angle

The compass angle is defined as the angle from the north to the x-direction of the body frame. In the NED reference frame, the compass angle is the counter-clockwise angle from the positive-x direction of the NED frame to the positive-x direction of the body frame. The orientations input defines the rotational coordinate transformation from the reference frame to the body frame. The compass angles of the north, east, south, and west directions are 0, π/2, π, and 3π/2, respectively.

## References

[1] Gade, Kenneth. “The Seven Ways to Find Heading.” Journal of Navigation, vol. 69, no. 5, Sept. 2016, pp. 955–70.

## Version History

Introduced in R2023b