Vector Length calc - Trig anyone?

Ok I promise this will be easy for anyone with half a brain, but seeing as how I must have an appropriation of about 1/3rd normal size here goes...

I wish to calculate the vector position of a point (which is the centre point of a virtual circle path) when I know the length and angle of the intersecting line.

Thats a really crappy description isnt it!

I did a diagram to help. http://www.exhibitionisland.com/trigmare.gif

Basically I need to plot the point to turn around an arc (all that side of things is ok) when approaching the turn point from a non "full degree" angle (ie: 0, 90, 180, 270) - currently 45 degrees (or 225,315 etc).

Theres no problem when approaching from the full degrees, but I am stuck on working the calc out when its requiring 2 values... so I looked at cos, sin and tan and had a nervous breakdown..

I think (if I have read it correctly) that I must convert degrees to Radians using the Constant (DEG_TO_RAD) and then do this sort of thing:

length = radius_of_circle;
angle =

vector.x = length * llCos( (DEG_TO_RAD * 45) );
vector.y = length * llSin( (DEG_TO_RAD * 45) );

newpos = vector;
//do something with newpos

but quite frankly thats scaring me...

Erwin

The short, poorly described answer is that you should be converting certain points from rectangular to polar coordinates which is what you were doing with your sin/cos transformations.

The better answer would be to understand quaternions which makes trig look easy, but probably solves your problem gracefully.

http://wiki.secondlife.com/wiki/Rotation
http://en.wikipedia.org/wiki/Quaternion

Good luck.

Ok, first of all are we assuming that everything is happening parallel to the ground?

If so, it looks like you first need to find a unit vector (ie one with length = 1) that is at right angles to your original vector, then multiply it by 5m, then add the result to your original point.

However, there's one complication. There are 2 points that match that description - you also have one 5m away on the other side of the inbound vector. Do have any way of knowing which you want?

Hi Stephen

I posted the above in the middle of some fiddling.... to my suprise the calculation actually worked when I added a smal tweak...

I forgot to add the calculated length to the vector! DOH!!

vector.x = vector.x + length * llCos( (DEG_TO_RAD * 45) );
vector.y = vector.y + length * llSin( (DEG_TO_RAD * 45) );

I did that - added a known angle and bingo!

I flicked around the resources posted by you both as well - and my head is still spinning

Cheers for the help

Erwin