How to rotate points on 2D coordinate systems

I have some points on a 2D Cartesian coordinate system. I want to rotate all these points 90 degrees counterclockwise. What is the best solution? (When I work with 3D coordinates, I use “view” to change the view direction, but apparently, it doesn’t work with 2D coordinates)

Answer 1

[John Chilleri]

Hello,

You can rotate your points with a rotation matrix:

Here's a simple implementation,

% Create rotation matrix
theta = 90; % to rotate 90 counterclockwise
R = [cosd(theta) -sind(theta); sind(theta) cosd(theta)];

% Rotate your point(s)
point = [3 5]'; % arbitrarily selected
rotpoint = R*point;

The rotpoint is the 90 degree counterclockwise rotated version of your original point.

Hope this helps!

[Hassan Bosha]

How can i plot it ?

using trplot()

[George Abrahams]

@Hassan Bosha One option is my plotframe function on File Exchange. Hope it helps!

[Ria]

Hello, if you needed the rotation clockwise, could you just reverse each sign of cosd and sind?

[George Abrahams]

@Ria You have two options. First option, set theta, the angle of rotation, to -90. Second option, the inverse of a rotation matrix is its transpose, , so transpose the matrix. In MATLAB this is typically achieved with the .' syntax.

R = [cosd(-90) -sind(-90); sind(-90) cosd(-90)]

R = 2×2

0 1 -1 0

R = [cosd(90) -sind(90); sind(90) cosd(90)].'

R = 2×2

0 1 -1 0

Answer 2

[Amit]

Write and execute a MATLAB program for geometric modeling of a parametric circle with center at any point {xc,yc}, radius R and lying in the X-Y plane. Test your program with R=40 mm and center at both the origin and at {10,10} for estimating the point and tangent vector at any given parameter value 0<=u<=1.

Answer 3

[Amit]

Write and execute a MATLAB program for geometric modeling of a parametric circle with center at any point {xc,yc}, radius R and lying in the X-Y plane. Test your program with R=40 mm and center at both the origin and at {10,10} for estimating the point and tangent vector at any given parameter value 0<=u<=1.

Write the Matlab code for both the original parametric equation and computationally efficient parametric equation. Compare the computational times.

Answer 4

[Amit]

a) Write and execute a MATLAB program to plot a planar parametric curve whose x- and y- axis modeled using cubic polynomial of the form: X(u) =A*u^3+B*u+C Y(u) =E*u^3+F* u^2+G Where 0 ≤ u ≤ 1 is the parameter, and A, B, C, E, F, G are the polynomial coefficients. Your program should work for any user supplied input of these polynomial coefficients.

b) Write Matlab program to generate and plot a the Hermite cubic curve for any set of two control points and two tangent vectors. Validate your code with sample data given below: P0 = [1, 1], P’0 = [0.6, 0.8], P1= [8, 2] and P’1 = [-0.4472, -0.8944].

Also include in the program the facility of putting point at the specified u-value and an arrow for the tangent vector at that point.