Re: Ada / Boeing 777

[Alan Brain <aebrain@dynamite.com.au>]

mbk@caffeine.engr.utk.edu (Matt Kennel) wrote:

>The representation (aka implementation) of angle is wrong.  
>
>It should be a complex number of unit magnitude.  Rotations in any
>direction can be implemented as complex multiplication without any
>discontinuities, wrap around errors or problems at 0 or 180 or 360
>degrees.   
>
>This is an easy 2-d representation of the rotation group.  3-d is 
>trickier: either Euler angles or quaternions. 
>
>Don't just hack on the problem: transcend it. 
>
>See, sometimes physicists *can* be useful.  ;-) 


Us Engineers come across this problem often. IMHO the best, in fact the 
ONLY solution is to have something like RADIANS_TYPE, a real, and then 
use subtypes and I/O converters appropriately. So if you're communicating 
with a piece of kit that likes to give you BAMS, you just multiply by the 
constant FROM_BAMS and convert from fixed point to real accordingly. 
Similarly, for some applications, a human-readable readout of 0-359 is 
good; for others, 1-360. Mils, Revs, Radians and Degrees are all useful 
at one time or another: but keep your arithmetic operations in a common 
format, else that way lies madness.