SPHERE_GRID
Grids on a Sphere


SPHERE_GRID is a C library which constructs a grid of points over the surface of the unit sphere in 3D.

A grid on a sphere may mean a set of points, or a set of points and lines that connect them, or a set of points, lines that connect them, and the faces that are bounded by those lines.

A grid may be desired which simply organizes areas. In that case, something like the latitude and longitude lines on a globe may be sufficient, even though "evenly spaced" latitude and longitude lines result in grid cells that are close to rectangular near the equator, but become more asymmetric near the poles.

A grid may also be desired for sampling, that is, for choosing a set of points that are well spread across the sphere. A simple Monte Carlo approach can be used, although this means that the data is only well spread out in the long view; there may be local clusters and gaps.

Other grids are generated by drawing a spiral on the surface of the sphere, and choosing points at regular spacings along that line, or by projecting an icosahedron onto the surface of the sphere, which divides the surface into 20 congruent spherical triangles, and then dealing with the simpler issue of choosing points from the triangles.

The test program uses GNUPLOT to make images of some of the grids.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

SPHERE_GRID is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

CUBE_GRID, a C library which computes a grid of points over the interior of a cube in 3D.

DISK_GRID, a C library which computes a grid of points over the interior of a disk in 2D.

GNUPLOT, C programs which illustrate how a program can write data and command files so that gnuplot can create plots of the program results.

HYPERCUBE_GRID, a C library which computes a grid of points over the interior of a hypercube in M dimensions.

LINE_GRID, a C library which computes a grid of points over the interior of a line segment in 1D.

POLYGON_GRID, a C library which generates a grid of points over the interior of a polygon in 2D.

PYRAMID_GRID, a C library which computes a grid of points over the interior of the unit pyramid in 3D;

SIMPLEX_GRID, a C library which generates a grid of points over the interior of a simplex in M dimensions.

SPHERE_FIBONACCI_GRID, a C library which computes a grid of points using the Fibonacci spiral over the surface of a sphere in 3D.

SPHERE_LLQ_GRID, a C library which uses longitudes and latitudes to create grids of points, lines, and quadrilaterals on the surface of the unit sphere in 3D.

SPHERE_LLT_GRID, a C library which uses longitudes and latitudes to create grids of points, lines, and triangles on the surface of the unit sphere in 3D.

SQUARE_GRID, a C library which computes a grid of points over the interior of a square in 2D.

TRIANGLE_GRID, a C library which computes a grid of points over the interior of a triangle in 2D.

WEDGE_GRID, a C library which computes a grid of points over the interior of the unit wedge in 3D.

Reference:

  1. Edward Saff, Arno Kuijlaars,
    Distributing Many Points on a Sphere,
    The Mathematical Intelligencer,
    Volume 19, Number 1, 1997, pages 5-11.
  2. Richard Swinbank, James Purser,
    Fibonacci grids: A novel approach to global modelling,
    Quarterly Journal of the Royal Meteorological Society,
    Volume 132, Number 619, July 2006 Part B, pages 1769-1793.

Source Code:

Examples and Tests:

To see the XYZ data files and images of the sphere grids created by this example program, go to the SPHERE_GRID dataset directory.

List of Routines:

You can go up one level to the C source codes.


Last revised on 21 October 2013.