1. rotateing
I'm looking for formulars to rotate 2d and 3d points arround an objects centre
(x,y) (x,y,z) respectively.
I've tried:
deg/=100
new_x=(cos(deg)*x)-(sin(deg)*y)
new_y=(sin(deg)*x)+(cos(deg)*y)
seems to rotate O.K. but it's not what I'm looking for.
ie: the origen here is assumed to be at 0:0.
could some please point me in the right direction.
2. Re: rotateing
Ooh, matrices time.
Know anything about matrices and matrix math?
If not, I suggest you look for tutorials about them on the net.
This one is good: http://chortle.ccsu.edu/VectorLessons/vectorIndex.html
On Tue, 01 Mar 2005 20:27:48 -0800, Hayden McKay
<guest at rapideuphoria.com> wrote:
>
> posted by: Hayden McKay <hmck1 at dodo.com.au>
>
> I'm looking for formulars to rotate 2d and 3d points arround an objects centre
> (x,y) (x,y,z) respectively.
>
> I've tried:
> deg/=100
> new_x=(cos(deg)*x)-(sin(deg)*y)
> new_y=(sin(deg)*x)+(cos(deg)*y)
>
> seems to rotate O.K. but it's not what I'm looking for.
> ie: the origen here is assumed to be at 0:0.
>
> could some please point me in the right direction.
>
>
>
>
--
MrTrick
3. Re: rotateing
Hayden McKay wrote:
> I'm looking for formulars to rotate 2d and 3d points arround an objects centre
> (x,y) (x,y,z) respectively.
>
> I've tried:
> deg/=100
> new_x=(cos(deg)*x)-(sin(deg)*y)
> new_y=(sin(deg)*x)+(cos(deg)*y)
>
> seems to rotate O.K. but it's not what I'm looking for.
> ie: the origen here is assumed to be at 0:0.
>
> could some please point me in the right direction.
To rotate around a point, just subtract the coordinates from {x, y}
before rotating, and add it again after rotating.
integer origin_x, origin_y, x, y, new_x, new_y
atom deg
...
deg /= 100
new_x = cos(deg) * (x - origin_x) - sin(deg) * (y - origin_y) + origin_x
new_y = sin(deg) * (x - origin_x) + cos(deg) * (y - origin_y) + origin_y
--
The Internet combines the excitement of typing
with the reliability of anonymous hearsay.
tommy online: http://users.telenet.be/tommycarlier
tommy.blog: http://tommycarlier.blogspot.com
4. Re: rotateing
Ahh yes! thanks guys. Also there was another problem
deg/=100 needed to be "deg*PI/180" ie: radans even though all the info I
found on the internet used the word degrees.
so I coded this
function make_cos() sequence s s=tabletype() for i=0 to 360 do
s[i+1]=cos(i*PI/180) end for end function
function make_sin() sequence s s=tabletype() for i=0 to 360 do
s[i+1]=sin(i*PI/180) end for end function
constant lookup_cos=make_cos()
constant lookup_sin=make_sin()
I stress again thanks..
It should'nt be hard for me now to rotate a 3d coord arround an arbituary axis!
5. Re: rotateing
On Tue, 01 Mar 2005 22:51:14 -0800, Hayden McKay
<guest at rapideuphoria.com> wrote:
> I stress again thanks..
> It should'nt be hard for me now to rotate a 3d coord arround an arbituary
> axis!
Wait...
3d coords are much more difficult. With a 2d system, you just have a
single number, 'angle'.
With a 3d system, you either need to use a quarternion or a 3x3
rotation/scaling matrix.
Sounds horrible, but I would recommend the 3x3 matrix as it's a lot
faster, and you can set things up so it rotates and scales in the same
step.
--
MrTrick
