1 ## Copyright (C) 2007-2012 David Bateman
3 ## This file is part of Octave.
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6 ## under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation; either version 3 of the License, or (at
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20 ## @deftypefn {Function File} {@var{yi} =} griddatan (@var{x}, @var{y}, @var{xi}, @var{method}, @var{options})
22 ## Generate a regular mesh from irregular data using interpolation.
23 ## The function is defined by @code{@var{y} = f (@var{x})}.
24 ## The interpolation points are all @var{xi}.
26 ## The interpolation method can be @code{"nearest"} or @code{"linear"}.
27 ## If method is omitted it defaults to @code{"linear"}.
28 ## @seealso{griddata, delaunayn}
31 ## Author: David Bateman <dbateman@free.fr>
33 function yi = griddatan (x, y, xi, method, varargin)
43 method = tolower (method);
49 if (n != ni || size (y, 1) != m || size (y, 2) != 1)
50 error ("griddatan: dimensional mismatch");
54 ## tri = delaunayn(x, varargin{:});
59 if (strcmp (method, "nearest"))
60 ## search index of nearest point
61 idx = dsearchn (x, tri, xi);
63 yi(valid) = y(idx(valid));
65 elseif (strcmp (method, "linear"))
66 ## search for every point the enclosing triangle
67 [tri_list, bary_list] = tsearchn (x, tri, xi);
69 ## only keep the points within triangles.
70 valid = !isnan (tri_list);
71 tri_list = tri_list(!isnan (tri_list));
72 bary_list = bary_list(!isnan (tri_list), :);
73 nr_t = rows (tri_list);
75 ## assign x,y for each point of simplex
76 xt = reshape (x(tri(tri_list,:),:), [nr_t, n+1, n]);
77 yt = y(tri(tri_list,:));
79 ## Use barycentric coordinate of point to calculate yi
80 yi(valid) = sum (y(tri(tri_list,:)) .* bary_list, 2);
83 error ("griddatan: unknown interpolation METHOD");
89 %! [xx,yy] = meshgrid(linspace(-1,1,32));
90 %! xi = [xx(:), yy(:)];
91 %! x = (2 * rand(100,2) - 1);
92 %! x = [x;1,1;1,-1;-1,-1;-1,1];
93 %! y = sin(2*(sum(x.^2,2)));
94 %! zz = griddatan(x,y,xi,'linear');
95 %! zz2 = griddata(x(:,1),x(:,2),y,xi(:,1),xi(:,2),'linear');
96 %! assert (zz, zz2, 1e-10)
99 %! [xx,yy] = meshgrid(linspace(-1,1,32));
100 %! xi = [xx(:), yy(:)];
101 %! x = (2 * rand(100,2) - 1);
102 %! x = [x;1,1;1,-1;-1,-1;-1,1];
103 %! y = sin(2*(sum(x.^2,2)));
104 %! zz = griddatan(x,y,xi,'nearest');
105 %! zz2 = griddata(x(:,1),x(:,2),y,xi(:,1),xi(:,2),'nearest');
106 %! assert (zz, zz2, 1e-10)