Calculating Coordinates on a Sphere Using Trigonometry

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    Sphere Trigonometry
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SUMMARY

The discussion focuses on calculating coordinates on a sphere using trigonometric functions. The correct formulas for converting spherical coordinates to Cartesian coordinates are established as follows: x = R cos(θ) sin(φ), y = R sin(θ) sin(φ), and z = R cos(φ), where R is the radius of the sphere, θ is the horizontal angle (longitude), and φ is the co-latitude. The initial formulas presented were incorrect due to a misunderstanding of the angle definitions. The discussion references the Wikipedia page on sphere equations for further clarification.

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frogtag
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Can someone just check my maths to see if this is correct.

Hopefully, this should give the coordinates for a point on a sphere?

x = radius x cos(vert angle) x sin(hoz angle)
y = radius x cos(hoz angle)
z = radius x sin(vert angle) x sin(hoz angle)
 
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In polar coordinates, [itex]x= \rho cos(\theta) sin(\theta)[/itex], [itex]y= \rho sin(\theta) sin(\phi)[/itex], [itex]z= \rho cos(\phi)[/itex]. There [itex]\theta[/itex] is what I think you are calling the "horizontal angle"- the angle between the positive x-axis and the line from (0,0,0) to the point (x,y,0)- also sometimes called the "longitude". [itex]\phi[/itex] is the "co-latitude", the angle between the z-axis and the line from (0,0,0) to (x,y,z). [itex]\rho[/itex] is the straight line distance between (0,0,0) and (x,y,z).

For a sphere of radius R, this is [itex]x= R cos(\theta) sin(\theta)[/itex], [itex]y= R sin(\theta) sin(\phi)[/itex], [itex]z= R cos(\phi)[/itex].
 

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