how to plot a point on a sphere.

hi everybody..

I have a sphere with r=12.6 and center in [0 0 0]....I have on the plane z=-15 a series of points that i should plot on the sphere surface keeping into account the arclength of this projection the projection is centerd in (0 0 -15).. I've started with finding the angle that generates such a projection... arclength+radius*angle

but now i dont know what to do

[darova]

You can use cart2sph to find spherical coordinates of your points

Once you found angles you can just change radius and return to cartesian

You want to project your points of a sphere?

[luca antonioli]

no, I have the projenctions point.. I want that those points are backprojected onto the shpere surface!

[Bjorn Gustavsson]

If you really have the projection point as you claimed, you will have to explain what type of projection you want - it is not obvious how to project points on a plane with z = -15 onto a sphere with radius 12.6, when the projection point lies in that plane.

[luca antonioli]

it is like in my drawing..

[luca antonioli]

[darova]

Use this simple scheme to get Z coordinate

[Adam Danz]

I'm wondering the same thing Bjorn Gustavsson is wondering. If the floor plane was at depth -12.6 I could understand how you want to wrap the coordinate to the sphere. But the floor plane is at -15 which would give it a different radius.