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## Copyright (C) 2022 John W. Eaton
##
## This program is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## This program is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSEll. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} referenceSphere (@var{name}, @var{unit})
## Return the parameters of the named spherical object.
##
## Valid names are "Unit Sphere", "Sun", "Sun", "Mercury", "Venus",
## "Earth", "Moon", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune",
## and "Pluto". Case is not important.
##
## @var{unit} can be the name of any unit accepted by function
## validateLengthUnit.m. Also here case is not important.
##
## The output consists of a scalar struct with fields "Name", "LengthUnit",
## "Radius", "SemimajorAxis", "SemiminorAxis", "InverseFlattening",
## "Eccentricity", "Flattening", "ThirdFlattening", "MeanRadius",
## "SurfaceArea", and "Volume".
##
## Examples:
##
## @example
## >> E = referenceSphere ()
## E =
##
## scalar structure containing the fields:
##
## Name = Unit Sphere
## LengthUnit =
## Radius = 1
## SemimajorAxis = 1
## SemiminorAxis = 1
## InverseFlattening = Inf
## Eccentricity = 0
## Flattening = 0
## ThirdFlattening = 0
## MeanRadius = 1
## SurfaceArea = 12.566
## Volume = 4.1888
## @end example
##
## @example
## >> E = referenceSphere ("Earth", "km")
## E =
##
## scalar structure containing the fields:
##
## Name = Earth
## LengthUnit = km
## Radius = 6371
## SemimajorAxis = 6371
## SemiminorAxis = 6371
## InverseFlattening = Inf
## Eccentricity = 0
## Flattening = 0
## ThirdFlattening = 0
## MeanRadius = 6371.0
## SurfaceArea = 5.1006e+08
## Volume = 1.0832e+12
## @end example
##
## @seealso{validateLengthUnit, referenceEllipsiod}
## @end deftypefn
## Parts of this function were adapted from referenceEllipsoid.
function Sph = referenceSphere (name = "unit", unit = "")
if (! ischar (name))
error ("referenceSphere: NAME must be a string");
endif
if (! ischar (unit))
error ("referenceSphere: units name expected for input arg. #2");
endif
switch (lower (name))
case "sun"
Name = "Sun";
Radius = 694460000;
case "mercury"
Name = "Mercury";
Radius = 2439000;
case "venus"
Name = "Venus";
Radius = 6051000;
case "earth"
Name = "Earth";
Radius = 6371000;
case "moon"
Name = "Moon";
Radius = 1738000;
case "mars"
Name = "Mars";
Radius = 3390000;
case "jupiter"
Name = "Jupiter";
Radius = 69882000;
case "saturn"
Name = "Saturn";
Radius = 58235000;
case "uranus"
Name = "Uranus";
Radius = 25362000;
case "neptune"
Name = "Neptune";
Radius = 24622000;
case "pluto"
Name = "Pluto";
Radius = 1151000;
case "unit"
Name = "Unit Sphere";
Radius = 1.0;
otherwise
error ("referenceSphere: unrecognized sphere: %s", name);
endswitch
if (! strcmpi (name, "unit") && isempty (unit))
if (nargin == 2)
error ("referenceSphere: UNIT may not be empty for %s", Name);
else
unit = "Meters";
endif
endif
Sph = param_calc (Name, Radius, unit);
endfunction
function sph = param_calc (Name, Radius, unit)
if (! isempty (unit))
ratio = unitsratio (unit, "Meters");
Radius = Radius * ratio;
endif
sph.Name = Name;
sph.LengthUnit = unit;
sph.Radius = Radius;
sph.SemimajorAxis = Radius;
sph.SemiminorAxis = Radius;
sph.InverseFlattening = Inf;
sph.Eccentricity = 0;
sph.Flattening = 0;
sph.ThirdFlattening = 0;
sph.MeanRadius = Radius;
sph.SurfaceArea = 4 * pi * Radius^2;
sph.Volume = (4 * pi) / 3 * Radius^3;
endfunction
%!test
%! U = referenceSphere ("Unit");
%! assert (U.LengthUnit, "");
%! assert (U.Radius, 1);
%! assert (U.SemimajorAxis, 1);
%! assert (U.SemiminorAxis, 1);
%! assert (U.InverseFlattening, Inf);
%! assert (U.Eccentricity, 0);
%! assert (U.Flattening, 0);
%! assert (U.ThirdFlattening, 0);
%! assert (U.MeanRadius, 1);
%! assert (U.SurfaceArea, 4*pi);
%! assert (U.Volume, 4*pi/3);
%!error <NAME must be a string> referenceSphere (7i)
%!error <unrecognized sphere> referenceSphere ("yy")
%!error <unknown unit> referenceSphere ("Unit", "##not a unit@@")
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