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1 ## Copyright (C) 2007 David Bateman |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by |
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7 ## the Free Software Foundation; either version 2, or (at your option) |
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8 ## any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {[@var{idx}, @var{p}] =} tsearchn (@var{x}, @var{t}, @var{xi}) |
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22 ## Searches for the enclosing Delaunay convex hull. For @code{@var{t} = |
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23 ## delaunayn (@var{x})}, finds the index in @var{t} containing the |
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24 ## points @var{xi}. For points outside the convex hull, @var{idx} is NaN. |
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25 ## If requested @code{tsearchn} also returns the barycentric coorinates @var{p} |
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26 ## of the enclosing triangles. |
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27 ## @seealso{delaunay, delaunayn} |
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28 ## @end deftypefn |
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29 |
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30 function [idx, p] = tsearchn (x, t, xi) |
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31 if (nargin != 3) |
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32 print_usage (); |
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33 endif |
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34 |
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35 nt = size (t, 1); |
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36 [m, n] = size (x); |
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37 mi = size (xi, 1); |
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38 idx = nan (mi, 1); |
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39 p = nan (mi, n + 1); |
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40 |
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41 ni = [1:mi].'; |
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42 for i = 1 : nt |
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43 ## Only calculate the Barycentric coordinates for points that have not |
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44 ## already been found in a triangle. |
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45 b = cart2bary (x (t (i, :), :), xi(ni,:)); |
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46 |
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47 ## Our points xi are in the current triangle if |
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48 ## (all(b >= 0) && all (b <= 1)). However as we impose that |
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49 ## sum(b,2) == 1 we only need to test all(b>=0). Note need to add |
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50 ## a small margin for rounding errors |
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51 intri = all (b >= -1e-12, 2); |
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52 idx(ni(intri)) = i; |
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53 p(ni(intri),:) = b(intri, :); |
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54 ni(intri) = []; |
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55 endfor |
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56 endfunction |
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57 |
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58 function Beta = cart2bary (T, P) |
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59 ## Conversion of Cartesian to Barycentric coordinates. |
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60 ## Given a reference simplex in N dimensions represented by a |
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61 ## (N+1)-by-(N) matrix, and arbitrary point P in cartesion coordinates, |
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62 ## represented by a N-by-1 row vector can be written as |
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63 ## |
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64 ## P = Beta * T |
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65 ## |
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66 ## Where Beta is a N+1 vector of the barycentric coordinates. A criteria |
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67 ## on Beta is that |
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68 ## |
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69 ## sum (Beta) == 1 |
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70 ## |
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71 ## and therefore we can write the above as |
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72 ## |
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73 ## P - T(end, :) = Beta(1:end-1) * (T(1:end-1,:) - ones(N,1) * T(end,:)) |
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74 ## |
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75 ## and then we can solve for Beta as |
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76 ## |
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77 ## Beta(1:end-1) = (P - T(end,:)) / (T(1:end-1,:) - ones(N,1) * T(end,:)) |
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78 ## Beta(end) = sum(Beta) |
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79 ## |
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80 ## Note below is generalize for multiple values of P, one per row. |
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81 [M, N] = size (P); |
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82 Beta = (P - ones (M,1) * T(end,:)) / (T(1:end-1,:) - ones(N,1) * T(end,:)); |
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83 Beta (:,end+1) = 1 - sum(Beta, 2); |
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84 endfunction |
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85 |
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86 %!shared x, tri |
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87 %! x = [-1,-1;-1,1;1,-1]; |
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88 %! tri = [1, 2, 3]; |
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89 %!test |
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90 %! [idx, p] = tsearchn (x,tri,[-1,-1]); |
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91 %! assert (idx, 1) |
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92 %! assert (p, [1,0,0], 1e-12) |
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93 %!test |
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94 %! [idx, p] = tsearchn (x,tri,[-1,1]); |
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95 %! assert (idx, 1) |
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96 %! assert (p, [0,1,0], 1e-12) |
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97 %!test |
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98 %! [idx, p] = tsearchn (x,tri,[1,-1]); |
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99 %! assert (idx, 1) |
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100 %! assert (p, [0,0,1], 1e-12) |
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101 %!test |
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102 %! [idx, p] = tsearchn (x,tri,[-1/3,-1/3]); |
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103 %! assert (idx, 1) |
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104 %! assert (p, [1/3,1/3,1/3], 1e-12) |
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105 %!test |
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106 %! [idx, p] = tsearchn (x,tri,[1,1]); |
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107 %! assert (idx, NaN) |
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108 %! assert (p, [NaN, NaN, NaN]) |
