comparison toolboxes/FullBNT-1.0.7/graph/mk_2D_lattice.m @ 0:e9a9cd732c1e tip

first hg version after svn

+function G = mk_2D_lattice(nrows, ncols, con)
+% MK_2D_LATTICE Return adjacency matrix for nearest neighbor connected 2D lattice
+% G = mk_2D_lattice(nrows, ncols, con)
+% G(k1, k2) = 1 iff k1=(i1,j1) is a neighbor of k2=(i2,j2) 
+% (Two pixels are neighbors if their Euclidean distance is less than r.)
+% Default connectivity = 4.
+%
+% WE ASSUME NO WRAP AROUND. 
+%
+% This is the neighborhood as a function of con:
+%
+%  con=4,r=1  con=8,r=sqrt(2)   con=12,r=2   con=24,r=sqrt(8)
+%  nn            2nd order        4th order
+%                                  x         x x x x x
+%    x          x x x            x x x       x x x x x
+%  x o x        x o x          x x o x x     x x o x x
+%    x          x x x            x x x       x x x x x
+%                                  x         x x x x x
+%
+% Examples:
+% Consider a 3x4 grid
+%  1  4  7  10
+%  2  5  8  11
+%  3  6  9  12
+%  
+% 4-connected:
+% G=mk_2D_lattice(3,4,4);
+% find(G(1,:)) = [2 4]
+% find(G(5,:)) = [2 4 6 8]
+%
+% 8-connected:
+% G=mk_2D_lattice(3,4,8);
+% find(G(1,:)) = [2 4 5]
+% find(G(5,:)) = [1 2 3 4 6 7 8 9]
+
+% meshgrid trick due to Temu Gautama ([e-mail])
+
+if nargin < 3, con = 4; end
+
+switch con,
+ case 4, r = 1;
+ case 8, r = sqrt(2);
+ case 12, r = 2;
+ case 24, r = sqrt(8);
+ otherwise, error(['unrecognized connectivity ' num2str(con)])
+end
+
+
+npixels = nrows*ncols;
+
+[x y]=meshgrid(1:ncols, 1:nrows);
+M = [x(:) y(:)];
+M1 = repmat(reshape(M',[1 2 npixels]),[npixels 1 1]);
+M2 = repmat(M,[1 1 npixels]);
+%D = squeeze(sum(abs(M1-M2),2)); % Manhattan distance
+M3 = M1-M2;
+D = sqrt(squeeze(M3(:,1,:)) .^2 + squeeze(M3(:,2,:)) .^2); % Euclidean distance
+G = reshape(D <= r,npixels,npixels);
+G = setdiag(G, 0);