Coordinates problems. How to convert from one system to another

[Anestis_T]

Homework Statement

Hi

I got a problem with some simple modeling. The original code assumes a spherical cloud with a central source, and it assumes that the source sits at the centre of the sphere. I want to change this model and instead of using photons coming from the central source, I want to assume that the photons start from the surface of the sphere.

Homework Equations

The original parameters are:
Initial Location
xp = xs
yp = ys
zp = zs

Set the photon of travel ---------
! nxp=sint*cos(phi)
! nyp=sint*sin(phi)
! nzp=cost

I used spherical coordinates for the starting point (r,t,phi)

What sort of conversion is needed in the setting of the photon travel?

The Attempt at a Solution

Any hints/help is more than welcome

Thanks a lot in advance

 

[lippyka]

.To convert from spherical coordinates to Cartesian coordinates, you will need to use the following equations:x = r*cos(t)*cos(phi)y = r*cos(t)*sin(phi)z = r*sin(t)Therefore, you can set the initial location of the photon's starting point using the following:xp = r*cos(t)*cos(phi)yp = r*cos(t)*sin(phi)zp = r*sin(t)To set the direction of the photon's travel, you can use the following equations:nxp = -sin(t)*cos(phi)nyp = -sin(t)*sin(phi)nzp = cos(t)