vDSP_rectD

Declaration

extern void vDSP_rectD(const double *__A, vDSP_Stride __IA, double *__C, vDSP_Stride __IC, vDSP_Length __N);

Parameters

• __A:

  The input vector that contains adjacent pairs of coordinates.

• __IA:

  The distance between the adjacent coordinate pairs of elements in the input vector. This value must be an even number.

• __C:

  On output, the output vector that contains adjacent pairs of coordinates.

• __IC:

  The distance between the adjacent coordinate pairs of elements in the output vector. This value must be an even number.

• __N:

  The number of ordered pairs that the function processes.

Discussion

The function uses the following calculation to convert polar coordinates to rectangular coordinates:

for (n = 0; n < N; ++n)
{
    r     = A[n*IA+0];
    theta = A[n*IA+1];
    C[n*IC+0] = r * cos(theta);
    C[n*IC+1] = r * sin(theta);
}

Vector A defines the input polar (rho, theta) pairs, where rho is the radius and theta is the angle in the range [-pi, pi]. The function writes Cartesian (x, y) pairs to the output vector C. N specifies the number of coordinate pairs in A and C.

Coordinate pairs are adjacent elements in the array, regardless of stride; stride is the distance from one coordinate pair to the next.

The following code shows how to convert an angle-radius pair (with the angle specified in degress) to its rectangular equivalent.

let angle = Measurement(value: 45,
                        unit: UnitAngle.degrees)
    .converted(to: UnitAngle.radians)
    .value

let radius = sqrt(25.0 + 25.0)

let polarCoordinates = [radius, angle]

var rectangularCoordinates: [Double] = [0, 0]

let stride = vDSP_Stride(2)
let n = vDSP_Length(1)

vDSP_rectD(polarCoordinates, stride,
           &rectangularCoordinates, stride,
           n)

On return, rectangularCoordinates contains [5, 5].

This function performs the inverse operation of vDSP_polarD, which converts rectangular to polar coordinates.

See Also

Converting polar coordinates to rectangular coordinates

• vDSP_rect