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106 lines
3.0 KiB
106 lines
3.0 KiB
%DISTANCEXFORM Distance transform of occupancy grid
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%
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% D = DISTANCEXFORM(WORLD, GOAL) is the distance transform of the occupancy
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% grid WORLD with respect to the specified goal point GOAL = [X,Y]. The
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% elements of the grid are 0 from free space and 1 for occupied.
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%
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% D = DISTANCEXFORM(WORLD, GOAL, METRIC) as above but specifies the distance
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% metric as either 'cityblock' or 'Euclidean'
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%
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% D = DISTANCEXFORM(WORLD, GOAL, METRIC, SHOW) as above but shows an animation
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% of the distance transform being formed, with a delay of SHOW seconds between
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% frames.
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%
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% Notes::
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% - The Machine Vision Toolbox function imorph is required.
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% - The goal is [X,Y] not MATLAB [row,col]
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%
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% See also IMORPH, DXform.
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% Copyright (C) 1993-2011, by Peter I. Corke
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%
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% This file is part of The Robotics Toolbox for Matlab (RTB).
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%
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% RTB is free software: you can redistribute it and/or modify
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% it under the terms of the GNU Lesser General Public License as published by
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% the Free Software Foundation, either version 3 of the License, or
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% (at your option) any later version.
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%
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% RTB is distributed in the hope that it will be useful,
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% but WITHOUT ANY WARRANTY; without even the implied warranty of
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% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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% GNU Lesser General Public License for more details.
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%
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% You should have received a copy of the GNU Leser General Public License
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% along with RTB. If not, see <http://www.gnu.org/licenses/>.
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function d = distancexform(world, goal, metric, show)
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if exist('imorph', 'file') ~= 3
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error('Machine Vision Toolbox is required by this function');
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end
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if nargin < 4
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show = 0;
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end
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% set up the distance metrics
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if nargin < 3
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metric = 'cityblock';
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end
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if strncmpi(metric, 'cityblock', length(metric))
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m = ones(3,3);
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m(2,2) = 0;
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elseif strncmpi(metric, 'euclidean', length(metric))
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r2 = sqrt(2);
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m = [r2 1 r2; 1 0 1; r2 1 r2];
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else
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error('unknown distance metric');
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end
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% for the imorph primitive we need to set the target pixel to 0,
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% obstacles to NaN and the rest to Inf.
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if ~isempty(goal)
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% specific goal point
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if world(goal(2), goal(1)) > 0
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error('goal inside obstacle')
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end
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% point goal case
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world(world>0) = NaN;
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world(world==0) = Inf;
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world(goal(2), goal(1)) = 0;
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else
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world = double(world);
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world(world==0) = Inf;
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world(isfinite(world)) = 0;
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idisp(world)
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end
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count = 0;
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while 1
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world = imorph(world, m, 'plusmin');
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count = count+1;
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if show
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cmap = [1 0 0; gray(256)];
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colormap(cmap)
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image(world+1, 'CDataMapping', 'direct');
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set(gca, 'Ydir', 'normal');
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xlabel('x');
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ylabel('y');
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pause(show);
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end
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if ~any(isinf(world(:)))
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% stop if no Inf's left in the map
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break;
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end
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end
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if show
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fprintf('%d iterations\n', count);
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end
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d = world;
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