The result of rotation matrix rotx(angle) with a coordinate does not give the desired result

Hello All

I have a point with coordinates :

x y z : 0.00 60.00 225

and want to rotating it around the global X axis at the center 0,0,225 for 5 ° and get to the new coordinates :

x' y' z' : 0.00 59.96 225.95

the above new coordinates are in global CS and not in rotated CS

but if I use the rotx(5).* oldcoords

I don't get these values.

[James Tursa]

Can you show the basic math demonstrating how a 5 degree rotation will produce your desired values?

[farzad]

Well I could define it : each rotation is around the global axis directions, but with its center at (0,0,225)

In the order of xyz

[farzad]

Since I used CAD software to do it, I don't know with what mathematics I should define it for you

[Matt J]

It can be verified immediately that the separation between the two directions is not 5 degrees

v1=[ 0.00  60.00  225-225 ]; 
v2=[ 0.00  59.96  225.95-225];

>> SeparationAngle = acosd(dot(v1,v2)/norm(v1)/norm(v2))

SeparationAngle =

    0.9077

[farzad]

The separation angle you found is one single rotation. The rotation I defined is around x axis. Maybe your rotation is not around x axis but another axis in space

[Matt J]

Both v1 and v2 are in the y-z plane, so if the rotation was about the x-axis, then the separation of the two directions must be the rotation angle.

Answer 1

[Matt J]

Here's what my AxelRot utility gives

https://www.mathworks.com/matlabcentral/fileexchange/30864-3d-rotation-about-shifted-axis?focused=5191309&tab=function

>> AxelRot([0.00  60.00  225 ].',+5,[1,0,0],[0 0 ,225])

ans =

         0
   59.7717
  230.2293