CODEWITHSUNDEEP
matlabplot
James
James

Reputation: 347

Drawing 2D grid in matlab

I am trying to get a 2D grid using matlab with x >= -1 and y <= 1 with step size of 0.1 But I'm getting 3D grid with no proper step sizes. Any ideas?

My code:

[x, y] = meshgrid(-1:0.1:5, 0:0.1:1);
surf(x,y)

Upvotes: 1

Views: 6069

Answers (1)

rayryeng
rayryeng

Reputation: 104464

Do you just want to plot a bunch of 2D points? You use plot. Using your example, you would take your x,y points and simply put dot markers for each point. Convert them into 1D arrays first before you do this:

[X,Y] = meshgrid(-1:0.1:5, 0:0.1:1);
X = X(:);
Y = Y(:);
plot(X,Y,'b.');
xlabel('X'); % // Label the X and Y axes
ylabel('Y');

This is what I get:

enter image description here

Edit based on comments

If you want to rotate this grid by an angle, you would use a rotation matrix and multiply this with each pair of (x,y) co-ordinates. If you recall from linear algebra, to rotate a point counter-clockwise, you would perform the following matrix multiplication:

[x'] = [cos(theta) -sin(theta)][x]
[y']   [sin(theta)  cos(theta)][y]

x,y are the original co-ordinates while x',y' are the output co-ordinates after rotation of an angle theta. If you want to rotate -30 degrees (which is 30 degrees clockwise), you would just specify theta = -30 degrees. Bear in mind that cos and sin take in their angles as radians, so this is actually -pi/6 in radians. What you need to do is place each of your points into a 2D matrix. You would then use the rotation matrix and apply it to each point. This way, you're vectorizing the solution instead of... say... using a for loop. Therefore, you would do this:

theta = -pi/6; % // Define rotation angle
rot = [cos(theta) -sin(theta); sin(theta) cos(theta)]; %// Define rotation matrix
rotate_val = rot*[X Y].'; %// Rotate each of the points
X_rotate = rotate_val(1,:); %// Separate each rotated dimension
Y_rotate = rotate_val(2,:);
plot(X_rotate, Y_rotate, 'b.'); %// Show the plot
xlabel('X');
ylabel('Y');

This is what I get:

enter image description here

If you wanted to perform other transformations, like scaling each axis, you would just multiply either the X or Y co-ordinates by an appropriate scale:

X_scaled = scale_x*X;
Y_scaled = scale_y*Y;

X_scaled and Y_scaled are the scaled versions of your co-ordinates, with scale_x and scale_y are the scales in each dimension you want. If you wanted to translate the co-ordinates, you would add or subtract each of the dimensions by some number:

X_translate = X + X_shift; %// Or -
Y_translate = Y + Y_shift; %// Or -

X_translate and Y_translate are the translated co-ordinates, while X_shift and Y_shift are the amount of shifts you want per dimension. Note that you either do + or -, depending on what you want.

Upvotes: 3

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