Math wizardry

[Roger.E.Eller at sealedair.com]

On Tue, 29 Mar 2005 05:13:44 -0800, Jim Hurley wrote to Jim MaConnell:
>
> Jim,
> Perhaps even easier would be to define a function which determines
> the *geometrical* angle associated with a line in Run Rev. Any
> geometrical line rotated 180 degrees is the same geometrical line.
> Therefore the function below eliminates the signs associated with
> Run Rev angle.
> 
> 
> function theGeometrialAngle p1,p2
>   --Geometrical angle of line defined by the two points p1 and p2
>   get the paramcount
>   if it is 1 then
>     put line 2 of p1 into p2
>     put line 1 of p1 into p1
>   end if
>   put item 1 of p2 - item 1 of p1 into dx
>   put item 2 of p2 - item 2 of p1 into dy
>   put atan2(dy,dx) into tAngle
>   --Add or subtract pi as needed.
>   switch
>   case  tAngle < 0
>     return tAngle + pi
>     break
>   case  tAngle > pi
>     return tAngle - pi
>     break
>   default
>     return tAngle
>   end switch
> end theGeometrialAngle
> 
> function tAngleBetween a1,a2
>   return abs(a1 - a2)
> end tAngleBetween
> And so the geometrical angle between two Run Rev lines is just the 
absolute value of the difference.
> 
> 
> Jim

Hello Jim(s),

I was trying to use this function with a real-world problem and it isn't 
giving me the result (an angle between 1 and 360) that I expected. I have 
an image object (a scan of some text). The image wasn't scanned straight, 
so I thought I would draw a grc line in parallel with the text in the 
scan. I am trying to use the functions above to determine the angle of the 
grc line object so that I can rotate the image to make it straight. The 
function always returns a number that is less than 3. Can someone explain 
why this is or offer another way to determine the angle of a line? Math is 
NOT my strength.

TIA,
Roger Eller <roger.e.eller at sealedair.com>