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local2globalcoord

Convert local to global coordinates

Syntax

gCoord = local2globalcoord(lclCoord,OPTION)
gCoord = local2globalcoord(___,localOrigin)
gCoord = local2globalcoord(___,localAxes)

Description

gCoord = local2globalcoord(lclCoord,OPTION) converts local coordinates lclCoord to global coordinates gCoord. OPTION determines the type of local-to-global coordinate transformation.

gCoord = local2globalcoord(___,localOrigin) specifies the origin of the local coordinate system, localOrigin.

gCoord = local2globalcoord(___,localAxes) specifies the axes of the local coordinate system, localAxes.

Input Arguments

lclCoord

Local coordinates in rectangular or spherical coordinate form, specified as a 3-by-N matrix. Each column represents one set of local coordinates.

If the coordinates are in rectangular form, each column contains the (x,y,z) components. Units are in meters.

If the coordinates are in spherical form, each column contains (az,el,r) components. az is the azimuth angle in degrees, el is the elevation angle in degrees, and r is the radius in meters.

OPTION

Types of coordinate transformations, specified as a character vector. Valid values are

OPTIONTransformation
'rr'Local rectangular to global rectangular
'rs'Local rectangular to global spherical
'sr'Local spherical to global rectangular
'ss'Local spherical to global spherical

localOrigin

Origin of local coordinate system, specified as a 3-by-N matrix containing the rectangular coordinates of the local coordinate system origin with respect to the global coordinate system. N must match the number of columns of gCoord. Each column represents a separate origin. However, you can specify localOrigin as a 3-by-1 vector. In this case, localOrigin is expanded into a 3-by-N matrix with identical columns.

Default: [0;0;0]

localAxes

Axes of local coordinate system, specified as a 3-by-3-by-N array. Each page contains a 3-by-3 matrix representing a different local coordinate system axes. The columns of the 3-by-3 matrices specify the local x, y, and z axes in rectangular form with respect to the global coordinate system. However, you can specify localAxes as a single 3-by-3 matrix. In this case, localAxes is expanded into a 3-by-3-by-N array with identical 3-by-3 matrices. The default is the identity matrix.

Default: [1 0 0;0 1 0;0 0 1]

Output Arguments

gCoord

Glabal coordinates in rectangular or spherical coordinate form, returned as a 3-by-N matrix. The dimensions of gCoord match the dimensions of lclCoord. The origin of the global coordinate system is assumed to be located at (0, 0, 0). The global system axes are the standard unit basis vectors in three-dimensional space, (1, 0, 0), (0, 1, 0), and (0, 0, 1).

Examples

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Convert from local rectangular coordinates to global rectangular coordinates. The local coordinate origin is a (1,1,1)

globalcoord = local2globalcoord([0;1;0], 'rr',[1;1;1])
globalcoord = 3×1

     1
     2
     1

Convert local spherical coordinate to global rectangular coordinate.

globalcoord = local2globalcoord([30;45;4],'sr')
globalcoord = 3×1

    2.4495
    1.4142
    2.8284

Convert two vectors in global coordinates into two vectors in global coordinates using the global2local function. Then convert them back to local coordinates using the local2global function.

Start with two vectors in global coordinates, (0,1,0) and (1,1,1). The local coordinate origins are (1,5,2) and (-4,5,7).

gCoord = [0 1; 1 1; 0 1]
gCoord = 3×2

     0     1
     1     1
     0     1

lclOrig = [1 -4; 5 5; 2 7];

Construct two rotation matrices using the rotation functions.

lclAxes(:,:,1) = rotz(45)*roty(-15);
lclAxes(:,:,2) = roty(45)*rotx(35);

Convert the vectors in global coordinates into local coordinates.

lclCoord = global2localcoord(gCoord,'rr',lclOrig,lclAxes)
lclCoord = 3×2

   -3.9327    7.7782
   -2.1213   -3.6822
   -1.0168    1.7151

Convert the vectors in local coordinates back into global coordinates.

gCoord1 = local2globalcoord(lclCoord,'rr',lclOrig,lclAxes)
gCoord1 = 3×2

   -0.0000    1.0000
    1.0000    1.0000
         0    1.0000

More About

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Azimuth Angle, Elevation Angle

The azimuth angle of a vector is the angle between the x-axis and the orthogonal projection of the vector onto the xy plane. The angle is positive in going from the x axis toward the y axis. Azimuth angles lie between –180 and 180 degrees. The elevation angle is the angle between the vector and its orthogonal projection onto the xy-plane. The angle is positive when going toward the positive z-axis from the xy plane. These definitions assume the boresight direction is the positive x-axis.

Note

The elevation angle is sometimes defined in the literature as the angle a vector makes with the positive z-axis. The MATLAB® and Phased Array System Toolbox™ products do not use this definition.

This figure illustrates the azimuth angle and elevation angle for a vector that appears as a green solid line. The coordinate system is relative to the center of a uniform linear array, whose elements appear as blue circles.

References

[1] Foley, J. D., A. van Dam, S. K. Feiner, and J. F. Hughes. Computer Graphics: Principles and Practice in C, 2nd Ed. Reading, MA: Addison-Wesley, 1995.

Extended Capabilities

Introduced in R2011a