maths problem

[size13]

if the blue line can rotate, like a car speedo
how do I get the position at which it intersects the circle (red cross) as an x, y coordinate from the top left?

p.s. click the pic to make it look better. in this example, the image is 1000 x 500

Edited by size13 on Tuesday 4th July 17:46

[M@H]

http://planetmath.org/encyclopedia/Ci

see "The circle in analytic geometry"

Cheers
Matt

[funkynige]

Well, assuming you want the position as a function of the angle of the blue line from the horizontal...
the x coordinate from the origin is the radius of the circle times the sine of the angle the blue line makes with the horizontal.
the y coordinate from the origin is the radius of the circle times the cosine of the angle the blue line makes with the horizontal.

That will give coordinates from the centre of the circle, I'm sure you can go from there.

[pdV6]

Looks like a simple SOH CAH TOA, as presumably you know the radius of the circle and are given an angle to work from.

[size13]

funkynige said:

Well, assuming you want the position as a function of the angle of the blue line from the horizontal...
the x coordinate from the origin is the radius of the circle times the sine of the angle the blue line makes with the horizontal.
the y coordinate from the origin is the radius of the circle times the cosine of the angle the blue line makes with the horizontal.

That will give coordinates from the centre of the circle, I'm sure you can go from there.

spot on, thanks