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I use:
Ang = angle in radians
Fnc=function(x,y,z,Ang){Fna((x-.50)*cos(Ang)+(y-.433)*sin(Ang)+.50,
-(x-.50)*sin(Ang)+(y-.433)*cos(Ang),1)+.433};
to rotate a egualaterial triangle in place whose base is at <0,0,0> to
<1,0,0> and peak is at <.5,.866,0>.
It works when Ang=0.
But doesn't when Ang=radians(120) or Ang=radians(120).
Any Ideas?
I've even try translating another corner of triangle to <0,0,0>
rotating then translating back. Close but there's a noticable gap
from the true triangle.
Post a reply to this message
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Leroy Whetstone <lrw### [at] joplin com> wrote:
> I use:
> Ang = angle in radians
> Fnc=function(x,y,z,Ang){Fna((x-.50)*cos(Ang)+(y-.433)*sin(Ang)+.50,
> -(x-.50)*sin(Ang)+(y-.433)*cos(Ang),1)+.433};
> to rotate a egualaterial triangle in place whose base is at <0,0,0> to
> <1,0,0> and peak is at <.5,.866,0>.
> It works when Ang=0.
> But doesn't when Ang=radians(120) or Ang=radians(120).
>
> Any Ideas?
>
> I've even try translating another corner of triangle to <0,0,0>
> rotating then translating back. Close but there's a noticable gap
> from the true triangle.
Maybe because you're not perfectly sure what point you should be rotating it
about?
From your formula I gather that you are rotating about <1/2,.866/2,0>. However,
the described equilateral triangle's centroid (i.e. the "center of mass" so to
speak) is at <1/2,.866/3,0>.
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clipka wrote:
> Maybe because you're not perfectly sure what point you should be rotating it
> about?
>
> From your formula I gather that you are rotating about <1/2,.866/2,0>. However,
> the described equilateral triangle's centroid (i.e. the "center of mass" so to
> speak) is at <1/2,.866/3,0>.
>
>
>
Your right! Thanks for the help. I was trying to rotate from the center
of the box contanting the triangle.
I now use the more percise .5*tan(radian(30)) for the y adjust.
Also I had the y componet added to the whole function:
Fnc=function(x,y,z,Ang){Fna((x-.50)*cos(Ang)+(y-.433)*sin(Ang)+.50,
-(x-.50)*sin(Ang)+(y-.433)*cos(Ang),1)+.433};
^ ^^^^^
| This
Should be here
But now that's taken care of, I get a nice little cracks. (picture attached)
Have fun!
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Attachments:
Download 'colors001.gif' (3 KB)
Preview of image 'colors001.gif'
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Found the Fix!
#local H30=.5*tan(radians(30));
#local H60=sin(radians(60));
#local
Fnc=function(x,y,z,Ang){Fna((x-.50)*cos(Ang)+(y*H60-H30)*sin(Ang)+.50,
-(x-.50)*sin(Ang)+(y*H60-H30)*cos(Ang)+H30,0)};
Don't know Why it works but it does!!
Have Fun!
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