## Copyright (C) 2017 Philip Nienhuis ## ## 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 PURPOSE. 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. If not, see . ## -*- texinfo -*- ## @deftypefn {} {@var{lat_o, lon_o} =} antipode (@var{lat_i}, @var{lon_i}) ## @deftypefnx {} {@var{lat_o, lon_o} =} antipode (@var{lat_i}, @var{lon_i}, @var{unit}) ## Compute antipode (opposite point on globe). ## ## @var{lat_i} and @var{lon_i} (numeric values) are input latitude and ## longitude, optionally vectors. ## ## Optional argument @var{unit} can be one of 'Degrees' or 'Radians') and ## can be used to specify the input units. Just one 'd' or 'r' ## (case-insensitive) will do. ## ## @end deftypefn ## Author: Philip Nienhuis ## Created: 2017-03-02 function [lato, lono] = antipode (lati, loni, unit="") if (nargin < 2 || nargout < 2) print_usage (); elseif (! isnumeric (lati) || ! isnumeric (loni)) error ("antipode: numeric arguments expected for latitude and longitude\n"); elseif (! ischar (unit)) error ("antipode: character argument expected for lat/lon unit\n"); elseif (nargin > 3 && ! ismember (lower (unit(1)), {"d", "r"})) error ("antipode: units must be one of 'Degrees' of 'Radians'"); endif if (strncmpi (lower (unit), "r", 1)) convfac = 180.0 / pi; lati *= convfac; loni *= convfac; endif lato = -abs (180.0 - wrapTo360 (lati - 90.0)) + 90.0; lono = wrapTo180 (loni + 180); if (strncmpi (lower (unit), "r", 1)) lato /= convfac; lono /= convfac; endif endfunction %!test %! [lato, lono] = antipode (90, 0); %! assert ([lato, lono], [-90, 180], eps); %!test %! [lato, lono] = antipode (43, 15); %! assert ([lato, lono], [-43, -165], eps);