cart2sph: Coordinate Transformations

In pracma: Practical Numerical Math Functions

Coordinate Transformations

Description

Transforms between cartesian, spherical, polar, and cylindrical coordinate systems in two and three dimensions.

Usage

cart2sph(xyz)
sph2cart(tpr)
cart2pol(xyz)
pol2cart(prz)

Arguments

xyz	cartesian coordinates x, y, z as vector or matrix.
tpr	spherical coordinates theta, phi, and r as vector or matrix.
prz	polar coordinates phi, r or cylindrical coordinates phi, r, z as vector or matrix.

Details

The spherical coordinate system used here consists of

- theta, azimuth angle relative to the positive x-axis

- phi, elevation angle measured from the reference plane

- r, radial distance. i.e., distance to the origin

The polar angle, measured with respect from the polar axis, is then calculated as pi/2 - phi. Note that this convention differs slightly from spherical coordinates (r, theta, phi) as often used in mathematics, where phi is the polar angle.

cart2sph returns spherical coordinates as (theta, phi, r), and sph2cart expects them in this sequence.

cart2pol returns polar coordinates (phi, r) if length(xyz)==2 and cylindrical coordinates (phi, r, z) else. pol2cart needs them in this sequence and length.

To go from cylindrical to cartesian coordinates, transform to cartesian coordinates first — or write your own function, see the examples.

All transformation functions are vectorized.

Value

All functions return a (2- or 3-dimensional) vector representing a point in the requested coordinate system, or a matrix with 2 or 3 named columns where is row represents a point. The columns are named accordingly.

Note

In Matlab these functions accept two or three variables and return two or three values. In R it did not appear appropriate to return coordinates as a list.

These functions should be vectorized in the sense that they accept will accept matrices with number of rows or columns equal to 2 or 3.

Examples

x <- 0.5*cos(pi/6); y <- 0.5*sin(pi/6); z <- sqrt(1 - x^2 - y^2)
(s <-cart2sph(c(x, y, z)))      # 0.5235988 1.0471976 1.0000000
sph2cart(s)                     # 0.4330127 0.2500000 0.8660254

cart2pol(c(1,1))                # 0.7853982 1.4142136
cart2pol(c(1,1,0))              # 0.7853982 1.4142136 0.0000000
pol2cart(c(pi/2, 1))            # 6.123234e-17 1.000000e+00
pol2cart(c(pi/4, 1, 1))         # 0.7071068 0.7071068 1.0000000

##  Transform spherical to cylindrical coordinates and vice versa
#   sph2cyl <- function(th.ph.r) cart2pol(sph2cart(th.ph.r))
#   cyl2sph <- function(phi.r.z) cart2sph(pol2cart(phi.r.z))

pracma documentation built on March 19, 2024, 3:05 a.m.