binary occupancy map flipped after using A* algorithm

I am trying to explore A* algorithm which is built-in MATLAB algorithm, but when creating enviornment for simulation and then show the outcome of the planner the result is flipped compared to original map.

the code used as follow:

clearvars;
close all;
% Parameters
x_max = 500;
y_max = 500;
mapRes = 1; % 1 cell per meter (or per unit)
%  number of obstacles
numObstacles = input('Enter the number of rectangular obstacles: ');
% Obstacle size
obsWidth = 40;
obsHeight = 40;
% Create empty map
mapMatrix = zeros(y_max, x_max); % Rows = Y, Columns = X
% Add rectangular obstacles
for i = 1:numObstacles
    x = randi([1, x_max - obsWidth]);
    y = randi([1, y_max - obsHeight]);
    mapMatrix(y:(y+obsHeight), x:(x+obsWidth)) = 1; % Occupied = 1
end
% Flip the map vertically so that origin is at bottom-left (for A*)
mapMatrix = flipud(mapMatrix);
% Create binary occupancy map
map = binaryOccupancyMap(mapMatrix, mapRes);
% Flip axis for plotting purposes
figure;
show(map);
set(gca, 'YDir', 'normal');  % Flip Y axis so origin is bottom-left
title('Click to select START (green) and GOAL (red)');
hold on;
% Select start point
disp('Click on the map to select the START point');
[startX, startY] = ginput(1);
start = round([startY, startX]);
plot(start(2), start(1), 'go', 'MarkerSize', 10, 'LineWidth', 2);
% Select goal point
disp('Click on the map to select the GOAL point');
[goalX, goalY] = ginput(1);
goal = round([goalY, goalX]);
plot(goal(2), goal(1), 'ro', 'MarkerSize', 10, 'LineWidth', 2);
% % Flip the map
% mapFliped = flipud(map);
% figure;
% show(mapFliped)
% Plan using A* algorithm
planner = plannerAStarGrid(map);
[path, debugInfo] = plan(planner, start, goal);
% Display results
figure;
show(planner);
% plot(path(:,2), path(:,1))
set(gca, 'YDir', 'normal');  % Flip Y axis again
axis xy;
title('A* Path Planning Result');
% legend('Path','Start','Goal','Explored');

[Walter Roberson]

Not sure what else you should expect considering the

mapMatrix = flipud(mapMatrix);

[YAAQOB AL-JAMALI]

so if i assign to a different variable it is going to work. do i understand you correctly

[Walter Roberson]

I am suggesting commenting out that line.

[YAAQOB AL-JAMALI]

i have commented it out, yet the content of the map still flipped. I do think there is some feature in A* algorithm which cause this but not really sure. If you know a step to overcome such nature, I would appreciate it.

Answer 1

[Cris LaPierre]

You need to specify 'world' as an additional input to plan when start and goal are specified as [x y] in world coordinate frame with origin at bottom-left corner.

path = plan(planner,start,goal,'world')

With this setting, you do not need to worry about flipping or setting axis Y direction.

% Parameters
x_max = 500;
y_max = 500;
mapRes = 1; % 1 cell per meter (or per unit)
%  number of obstacles
numObstacles = 8;%input('Enter the number of rectangular obstacles: ');
% Obstacle size
obsWidth = 40;
obsHeight = 40;
% Create empty map
mapMatrix = zeros(y_max, x_max); % Rows = Y, Columns = X
% Add rectangular obstacles
for i = 1:numObstacles
    x = randi([1, x_max - obsWidth]);
    y = randi([1, y_max - obsHeight]);
    mapMatrix(y:(y+obsHeight), x:(x+obsWidth)) = 1; % Occupied = 1
end

% Create binary occupancy map
map = binaryOccupancyMap(mapMatrix, mapRes);
figure;
show(map);
hold on;

start = [28 48];
plot(start(2), start(1), 'go', 'MarkerSize', 10, 'LineWidth', 2);
goal = [481, 418];
plot(goal(2), goal(1), 'ro', 'MarkerSize', 10, 'LineWidth', 2);
hold off

planner = plannerAStarGrid(map);
[path, debugInfo] = plan(planner, start, goal,'world');
% Display results
figure;
show(planner);
title('A* Path Planning Result');

[YAAQOB AL-JAMALI]

thank you so much, that is really work more better than the way i figure it out.