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## Copyright (C) 2019-2022 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 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} {@var{zone} =} utmzone (@var{lat} , @var{long})
## @deftypefnx {Function File} {@var{latlon} =} utmzone (@var{zone})
## @deftypefnx {Function File} {@var{lat}, @var{long} =} utmzone (@var{zone})
## Returns the zone given a latitude and longitude, or the latitude and
## longitude ranges given a zone.
##
## Examples:
##
## @example
## utmzone (43, -79)
## => ans =
## 17T
## @end example
##
## Can also handle the special zones of Norway
##
## @example
## utmzone (60, 5)
## => ans =
## 32V
## @end example
##
## For zones:
##
## @example
## utmzone ("17T")
## => ans =
## 40 48
## -84 -78
## @end example
##
## @example
## [lat, lon] = utmzone ("17T")
## =>
## lat =
## 40 48
## lon =
## -84 -78
## @end example
##
## @end deftypefn
## Function supplied by anonymous contributor, see:
## https://savannah.gnu.org/patch/index.php?9756
function [zone, z2] = utmzone (lat, long)
## Since there is no I or O, the last 4 are special cases
alphabet = ("CDEFGHJKLMNPQRSTUVWXABYZ");
if (nargin < 2)
if (ischar (lat) && numel (lat) > 1)
num = sscanf (lat, "%f");
if (num < 1)
error ("utmzone: positive number expecte for zone");
endif
let = find (alphabet == upper (lat(end)));
if (isempty (let))
error ("utmzone: incorrect or no letter specified");
endif
switch upper (lat(end))
case "A"
lat = [-80 -90];
long = [-180 0];
zone = [lat; long];
case "B"
lat = [-80 -90];
long = [0 180];
zone = [lat; long];
case "Y"
lat = [84 90];
long = [-180 0];
zone = [lat; long];
case "Z"
lat = [84 90];
long = [0 180];
zone = [lat; long];
case "X"
lat = [72 84];
switch num
case 31
long = [0 9];
case 33
long = [9 21];
case 35
long = [21 33];
case 37
long = [33 42];
case {32, 34, 36}
error ("utmzone: zone %2iX does not exist", num);
otherwise
long = [(num - 1) * 6 - 180, (num * 6 - 180)];
endswitch
zone = [lat; long];
case "V"
lat = [56 64];
switch num
case 31
long = [0 3];
case 32
long = [3 12];
otherwise
long = [(num - 1) * 6 - 180, (num * 6 - 180)];
endswitch
zone = [lat; long];
otherwise
lat = [(let - 1) * 8 - 80, (let * 8) - 80 ];
long = [(num - 1) * 6 - 180, (num * 6 - 180)];
zone = [lat; long];
endswitch
endif
if (nargout ==2)
zone = lat;
z2 = long;
endif
elseif (isnumeric (lat) && isreal (lat) && isnumeric (long) && isreal (long))
lat = mean (lat);
long = mean (long);
if (lat <= -80)
if (long < 0)
zone = "A";
else
zone = "B";
endif
elseif (lat >= 84)
if long < 0
zone = "Y";
else
zone = "Z";
endif
elseif (lat >= 72 && lat < 84)
if (long >= 0 && long < 9)
zone = "31X";
elseif (long >= 9 && long < 21)
zone = "33X";
elseif (long >= 21 && long < 33)
zone = "35X";
elseif (long >= 33 && long < 42)
zone = "37X";
else
zone = zone (lat, long);
endif
elseif (lat >= 56 && lat < 64)
if (long >= 0 && long < 3)
zone = "31V";
elseif (long >= 3 && long < 12)
zone = "32V";
endif
else
zone = zone (lat, long);
endif
else
error ("utmzone: numeric input expected for LAT en LON");
endif
endfunction
function z = zone (lat, long)
alphabet = ("CDEFGHJKLMNPQRSTUVWX");
num = floor ((long + 180) / 6) + 1;
idx = -80;
ind = 0;
while (lat > idx)
idx = idx + 8;
ind = ind + 1;
endwhile
let = alphabet (ind);
z = strcat (num2str (num), let);
endfunction
%!test
%! lat = 43; ## From Wiki
%! long = -79;
%! assert (utmzone (lat, long), "17T")
%!assert (utmzone ("17T"), [40, 48;-84, -78])
%!assert (utmzone (60, 5), "32V") ## For Bergen Norway
%!assert (utmzone ("32V"), [56, 64;3, 12])
%!error <zone> utmzone ("32X")
%!error <incorrect> utmzone ("31I")
%!error <incorrect> utmzone ("31O")
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