OT - math question.

[Member 4148]

Originally posted by Imperator Fyron:
y position is not height.

can be - it depends on coordinate system used
there is no particular reason why the center of the sphere has to be the 0 point - he wanted the answer from the bottom of the sphere after all
likewise there is no particular reason why z has to be up, y back, and x right - reducing to circle makes y up using cartesian so it works as height

Originally posted by Imperator Fyron:
Not sure what I was thinking with arc length, but you definitely need the angles associated with the vector from the starting point to the ending point. The relative height is just the z component of that vector.

Treating the movement as along a circle only works if the only component that is changing is the z component. If x or y change (but not both), then it is no longer a circle, but an ellipse.

you forgetting - he constraining himself to move on surface of sphere - any 'straight line' path constrained so makes for a segment of a perfect circle from some perspective - if you choose that perspective, it reduces to a circle just fine
also, narf specified direction of travel - to the right - which pretty much forces a circle sgement anyway

[narf poit chez BOOM]

x is left/right, y is up/down, z is not used.

it's a random straight line x movement and i need the y position on the sphere that a line straight up would hit.

sorry for not being clear the first time. i guess i need to reread mathamatical Posts at least three times.

[Member 4148]

Originally posted by narf poit chez BOOM:
x is left/right, y is up/down, z is not used.

it's a random straight line x movement and i need the y position on the sphere that a line straight up would hit.

sorry for not being clear the first time. i guess i need to reread mathamatical Posts at least three times.

Oh. That's easier -
need: r: radius of sphere
d: distance traveled
want: h: height above bottom edge of sphere

edit: small mistake on co-ordinate system - fixed
h = r - sqrt(r - d^2)

notes:
not defined for |d| > r
above applies for lower edge
upper edge is h = r + sqrt(r - d^2)

[ February 19, 2004, 08:08: Message edited by: Member 4148 ]

[narf poit chez BOOM]

and if your wondering what you worked so hard on , think big bowling ball. no, bigger than that.

thanks, guys.

'coincedently', there's a new hazard in my game.

[Cipher7071]

Attack of the killer bowling balls...
Run for your lives!!!
....aaaarrrrrrrrrggggh....splat !


Incidentally, if the distance traveled is very small compared to the size of the ball, then you can probably make do with an approximation. In that case, the pythagorean theorum or the tangent function will probably do the trick.

[Fyron]

Originally posted by Member 4148:

quote:

---

Originally posted by Imperator Fyron:
y position is not height.

can be - it depends on coordinate system used
there is no particular reason why the center of the sphere has to be the 0 point - he wanted the answer from the bottom of the sphere after all
likewise there is no particular reason why z has to be up, y back, and x right - reducing to circle makes y up using cartesian so it works as height

---

No, it doesn't have to be, but it does certainly help if you either stick to a standard coordinate system or define the one you are working in.

[narf poit chez BOOM]

it's not the distance traveled - they're so big they flatten things.