> I found a neat approximation for an arctangent in radians of a value of X
> in [-1,1]:
>
> atan(X) = X / { 1 + 0.28 X*X }     error < 0.005, |X| < 1
>
> If I use 8-bit fixed point, then the denominator will require 9 bits,
> which
> creates an annoying problem with the division.

Hi Robert,

If the implementation of the arctan is for a PIC, then you may wish to
consider:

http://www.dattalo.com/technical/software/pic/arctan.asm

This also has a similar error (~1/200) and doesn't involve any annoying
division. On the other hand, the returned result is in normalized radians
and thus may require an addition multiplication to convert to what ever
units you're using. (However, it should be pointed out that the lookup
table can be converted into other units).


Scott
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