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azelaxes

Spherical basis vectors in 3-by-3 matrix form

Syntax

Description

example

A = azelaxes(az,el) returns a 3-by-3 matrix containing the components of the basis(e^R,e^az,e^el) at each point on the unit sphere specified by azimuth, az, and elevation, el. The columns of A contain the components of basis vectors in the order of radial, azimuthal and elevation directions.

Examples

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At the point located at 45° azimuth, 45° elevation, compute the 3-by-3 matrix containing the components of the spherical basis.

A = azelaxes(45,45)
A =

    0.5000   -0.7071   -0.5000
    0.5000    0.7071   -0.5000
    0.7071         0    0.7071

The first column of A contains the radial basis vector [0.5000; 0.5000; 0.7071]. The second and third columns are the azimuth and elevation basis vectors, respectively.

Input Arguments

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Azimuth angle specified as a scalar in the closed range [–180,180]. Angle units are in degrees. To define the azimuth angle of a point on a sphere, construct a vector from the origin to the point. The azimuth angle is the angle in the xy-plane from the positive x-axis to the vector's orthogonal projection into the xy-plane. As examples, zero azimuth angle and zero elevation angle specify a point on the x-axis while an azimuth angle of 90° and an elevation angle of zero specify a point on the y-axis.

Example: 45

Data Types: double

Elevation angle specified as a scalar in the closed range [–90,90]. Angle units are in degrees. To define the elevation of a point on the sphere, construct a vector from the origin to the point. The elevation angle is the angle from its orthogonal projection into the xy-plane to the vector itself. As examples, zero elevation angle defines the equator of the sphere and ±90° elevation define the north and south poles, respectively.

Example: 30

Data Types: double

Output Arguments

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Spherical basis vectors returned as a 3-by-3 matrix. The columns contain the unit vectors in the radial, azimuthal, and elevation directions, respectively. Symbolically we can write the matrix as

(e^R,e^az,e^el)

where each component represents a column vector.

More About

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Spherical basis

Spherical basis vectors are a local set of basis vectors which point along the radial and angular directions at any point in space.

The spherical basis vectors (e^R,e^az,e^el) at the point (az,el) can be expressed in terms of the Cartesian unit vectors by

e^R=cos(el)cos(az)i^+cos(el)sin(az)j^+sin(el)k^e^az=sin(az)i^+cos(az)j^e^el=sin(el)cos(az)i^sin(el)sin(az)j^+cos(el)k^.

This set of basis vectors can be derived from the local Cartesian basis by two consecutive rotations: first by rotating the Cartesian vectors around the y-axis by the negative elevation angle, -el, followed by a rotation around the z-axis by the azimuth angle, az. Symbolically, we can write

e^R=Rz(az)Ry(el)[100]e^az=Rz(az)Ry(el)[010]e^el=Rz(az)Ry(el)[001]

The following figure shows the relationship between the spherical basis and the local Cartesian unit vectors.

Algorithms

MATLAB® computes the matrix A from the equations

A = [cosd(el)*cosd(az), -sind(az), -sind(el)*cosd(az); ...
		cosd(el)*sind(az),  cosd(az), -sind(el)*sind(az); ...
		sind(el),           0,         cosd(el)];

Introduced in R2013a

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