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TooDice · Jun 18th, 2005, 7:17 PM

I have a problem where I need to find the x,y coordinates of a point on a circle.

Imagine a point at the origin. I need to be able to work out what the coordinates would be if it moved a certain number of units in a given direction in degrees.

For some reason, after spending an hour or so playing around with sine and cosine my head seems to be going in circles. Can anyone help?

EverLearning · Jun 18th, 2005, 8:19 PM

Is the trajectory circular with a certain radius, i.e. is it a unit circle?
If the problem were the other way around, it would have been a piece of cake, you would not have needed this extra information about radius, it would cancel out:
take arctan(y/x) and you have the angle!

EDIT:
Anyway, if the radius (r) is known or figured out somehow, then sin(a) = y/r, cos(a) = x/r; a - is the angle measured from the positive x-axis; so then you can get x and y.

TooDice · Jun 18th, 2005, 8:39 PM

Yeah. Basically, find the x,y coordinates of a point on a perfect circle that you would meet if you travelled from the origin in a given direction in degrees. The radius is a variable, but if we use a radius of 1 unit for this example I can just work the rest out fine.

I need a function similar to the progam Logo, where you could type:

(Toggle Plain Text)

RIGHT 33
FORWARD 100

The turtle would then move to the correct place. I need to be able to find the x,y coordinates of this point. Accuracy isn't really a problem as I'll round it to an integer anyway, it just needs to look right.

EDIT:

You happened to edit ur post as I replied. I'll rearrange that and see if I can clean up the mess I made earlier...

TooDice · Jun 18th, 2005, 8:59 PM

It worked a treat!

(Toggle Plain Text)

x = cos(a)*r
y = sin(a)*r

That was all I needed. Thanks!

I can safely go to sleep now without nightmares about A-level mathematics.

EverLearning · Jun 18th, 2005, 9:02 PM

What's A-level mathematics?

TooDice · Jun 18th, 2005, 9:08 PM

You know those guys who are obsessed with calculating Pi to infinite decimal places or finding prime numbers? It's when one of those guys decides to get into teaching.

EverLearning · Jun 18th, 2005, 9:10 PM

I suppose not, that must be a British thing

Well actually I do, one of them is my DiffEqs instructor

TooDice · Jun 18th, 2005, 9:18 PM

When I was at school, you did your A-levels at the age of 16-17. It was optional and you had to spend two years at college to do it. Nowadays, kids leave secondary school at 16 with three A-levels already under their belt.

No wonder why I can't get a decent job.

Rory · Jun 23rd, 2005, 7:56 AM

Quote:

Originally Posted by TooDice

When I was at school, you did your A-levels at the age of 16-17. It was optional and you had to spend two years at college to do it. Nowadays, kids leave secondary school at 16 with three A-levels already under their belt.

Actually we do them later than your generation, leaving at 18. AS (first year) is easier than the old A-Levels, but A2 is far harder, much closer to degree level.

EverLearning · Jun 18th, 2005, 9:27 PM

In my native country (Russia), everything used to be compulsory, regular exams, everyone on the same page (ah ... the joys of socialism), regular exams. But since couple years ago they are introducing some standardized cr@p

. Glad I'm out

Jun 18th, 2005, 7:17 PM	#1
TooDice Newbie Join Date: Jun 2005 Location: UK Posts: 14 Rep Power: 0	Finding a point on a circle [solved] I have a problem where I need to find the x,y coordinates of a point on a circle. Imagine a point at the origin. I need to be able to work out what the coordinates would be if it moved a certain number of units in a given direction in degrees. For some reason, after spending an hour or so playing around with sine and cosine my head seems to be going in circles. Can anyone help? Last edited by TooDice; Jun 18th, 2005 at 9:01 PM.

Jun 18th, 2005, 8:19 PM	#2
EverLearning Hobbyist Programmer Join Date: May 2005 Location: Indiana Posts: 130 Rep Power: 4	Is the trajectory circular with a certain radius, i.e. is it a unit circle? If the problem were the other way around, it would have been a piece of cake, you would not have needed this extra information about radius, it would cancel out: take arctan(y/x) and you have the angle! EDIT: Anyway, if the radius (r) is known or figured out somehow, then sin(a) = y/r, cos(a) = x/r; a - is the angle measured from the positive x-axis; so then you can get x and y. __________________ got math? yumm... "All men by nature desire to know" -Aristotle, Metaphysics Last edited by EverLearning; Jun 18th, 2005 at 8:36 PM.

Jun 18th, 2005, 8:39 PM	#3
TooDice Newbie Join Date: Jun 2005 Location: UK Posts: 14 Rep Power: 0	Yeah. Basically, find the x,y coordinates of a point on a perfect circle that you would meet if you travelled from the origin in a given direction in degrees. The radius is a variable, but if we use a radius of 1 unit for this example I can just work the rest out fine. I need a function similar to the progam Logo, where you could type: (Toggle Plain Text) RIGHT 33 FORWARD 100 RIGHT 33 FORWARD 100 The turtle would then move to the correct place. I need to be able to find the x,y coordinates of this point. Accuracy isn't really a problem as I'll round it to an integer anyway, it just needs to look right. EDIT: You happened to edit ur post as I replied. I'll rearrange that and see if I can clean up the mess I made earlier... __________________ If it squeals, don't smoke it. Last edited by TooDice; Jun 18th, 2005 at 8:41 PM.

Jun 18th, 2005, 8:59 PM	#4
TooDice Newbie Join Date: Jun 2005 Location: UK Posts: 14 Rep Power: 0	It worked a treat! (Toggle Plain Text) x = cos(a)r y = sin(a)r x = cos(a)r y = sin(a)r That was all I needed. Thanks! I can safely go to sleep now without nightmares about A-level mathematics. __________________ If it squeals, don't smoke it.

Jun 18th, 2005, 9:02 PM	#5
EverLearning Hobbyist Programmer Join Date: May 2005 Location: Indiana Posts: 130 Rep Power: 4	What's A-level mathematics? __________________ got math? yumm... "All men by nature desire to know" -Aristotle, Metaphysics

Jun 18th, 2005, 9:08 PM	#6
TooDice Newbie Join Date: Jun 2005 Location: UK Posts: 14 Rep Power: 0	You know those guys who are obsessed with calculating Pi to infinite decimal places or finding prime numbers? It's when one of those guys decides to get into teaching. __________________ If it squeals, don't smoke it.

Jun 18th, 2005, 9:10 PM	#7
EverLearning Hobbyist Programmer Join Date: May 2005 Location: Indiana Posts: 130 Rep Power: 4	I suppose not, that must be a British thing Well actually I do, one of them is my DiffEqs instructor __________________ got math? yumm... "All men by nature desire to know" -Aristotle, Metaphysics

Jun 18th, 2005, 9:18 PM	#8
TooDice Newbie Join Date: Jun 2005 Location: UK Posts: 14 Rep Power: 0	When I was at school, you did your A-levels at the age of 16-17. It was optional and you had to spend two years at college to do it. Nowadays, kids leave secondary school at 16 with three A-levels already under their belt. No wonder why I can't get a decent job. __________________ If it squeals, don't smoke it.

Jun 18th, 2005, 9:27 PM	#10
EverLearning Hobbyist Programmer Join Date: May 2005 Location: Indiana Posts: 130 Rep Power: 4	In my native country (Russia), everything used to be compulsory, regular exams, everyone on the same page (ah ... the joys of socialism), regular exams. But since couple years ago they are introducing some standardized cr@p . Glad I'm out __________________ got math? yumm... "All men by nature desire to know" -Aristotle, Metaphysics

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Programming Forums > Application Development > Other Programming Languages

Finding a point on a circle