Rotate Spherical Coordinates to find new Vector Magnitude

Dear Forum,

I am given a ,,. Does Matlab have a function to convert and find the from a new ?

[Ameer Hamza]

What is the link between these two points? If there is just rotation, then the magnitude will be the same, r2=r1.

[Chad]

Thank you. I am trying to solve for the new magnitude from the new .

[Chad]

For example, if At the new I believe .

[James Tursa]

Spherical coordinates typically are restricted to have r >= 0. What application do you have where you think you need to allow negative r values?

[Chad]

If I am given a vector in either x,y,z or what is the vector magnitude with a known . It can be negative.

[Ameer Hamza]

In case when r1=100, theta1=0, and phi1=0, and if by the negative value of r, you mean reversing the position vector, then in that case, you can say that r1=-100, theta1=180, and phi1=0 is equivalent to the first vector. But for any other value of theta and phi, you cannot get the same vector.

Answer 1

[Sindar]

It sounds like the goal is to find the projection of the vector along the direction defined by theta=100, phi=150. If this is the case, one way is:

[x2,y2,z2] = sph2cart(150*pi/180,100*pi/180,1);
[x1,y1,z1] = sph2cart(phi1*pi/180,theta1*pi/180,r1);
v12_proj = x1.*x2 + y1.*y2 + z1.*z2;

[Chad]

Yes. This is what I was after. Thank you!