1 ## Copyright (C) 2007-2012 David Bateman
3 ## This file is part of Octave.
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20 ## @deftypefn {Function File} {[@var{idx}, @var{p}] =} tsearchn (@var{x}, @var{t}, @var{xi})
21 ## Search for the enclosing Delaunay convex hull. For @code{@var{t} =
22 ## delaunayn (@var{x})}, finds the index in @var{t} containing the
23 ## points @var{xi}. For points outside the convex hull, @var{idx} is NaN.
24 ## If requested @code{tsearchn} also returns the Barycentric coordinates @var{p}
25 ## of the enclosing triangles.
26 ## @seealso{delaunay, delaunayn}
29 function [idx, p] = tsearchn (x, t, xi)
42 ## Only calculate the Barycentric coordinates for points that have not
43 ## already been found in a triangle.
44 b = cart2bary (x (t (i, :), :), xi(ni,:));
46 ## Our points xi are in the current triangle if
47 ## (all(b >= 0) && all (b <= 1)). However as we impose that
48 ## sum(b,2) == 1 we only need to test all(b>=0). Note need to add
49 ## a small margin for rounding errors
50 intri = all (b >= -1e-12, 2);
52 p(ni(intri),:) = b(intri, :);
57 function Beta = cart2bary (T, P)
58 ## Conversion of Cartesian to Barycentric coordinates.
59 ## Given a reference simplex in N dimensions represented by a
60 ## (N+1)-by-(N) matrix, and arbitrary point P in cartesion coordinates,
61 ## represented by a N-by-1 row vector can be written as
65 ## Where Beta is a N+1 vector of the barycentric coordinates. A criteria
70 ## and therefore we can write the above as
72 ## P - T(end, :) = Beta(1:end-1) * (T(1:end-1,:) - ones(N,1) * T(end,:))
74 ## and then we can solve for Beta as
76 ## Beta(1:end-1) = (P - T(end,:)) / (T(1:end-1,:) - ones(N,1) * T(end,:))
77 ## Beta(end) = sum(Beta)
79 ## Note below is generalize for multiple values of P, one per row.
81 Beta = (P - ones (M,1) * T(end,:)) / (T(1:end-1,:) - ones(N,1) * T(end,:));
82 Beta (:,end+1) = 1 - sum(Beta, 2);
86 %! x = [-1,-1;-1,1;1,-1];
89 %! [idx, p] = tsearchn (x,tri,[-1,-1]);
91 %! assert (p, [1,0,0], 1e-12)
93 %! [idx, p] = tsearchn (x,tri,[-1,1]);
95 %! assert (p, [0,1,0], 1e-12)
97 %! [idx, p] = tsearchn (x,tri,[1,-1]);
99 %! assert (p, [0,0,1], 1e-12)
101 %! [idx, p] = tsearchn (x,tri,[-1/3,-1/3]);
103 %! assert (p, [1/3,1/3,1/3], 1e-12)
105 %! [idx, p] = tsearchn (x,tri,[1,1]);
107 %! assert (p, [NaN, NaN, NaN])