Le 15/09/2018 à 19:07, Mike Horvath a écrit :
> I'm trying to adapt the following PDF to POV-Ray code for my
> planetarium/orrery.
> 
> https://ssd.jpl.nasa.gov/txt/aprx_pos_planets.pdf
> 
> How do I calculate the modulus -180 <= M <= +180?
> 

180 degrees, really ?
Can't they use a decent measure of angle, in Grades !

> Is it equal to this?
> 
>     mod(number+180,360)-180

Probably, as long as number is above -180 at start.

I never understood mod of negative value, and there might be divergent
definitions.

They seem to be using a referential for M to describe a full "circle",
so yes, they want to reduce the range of M to be between -180 and +180.

> 
> 
> Mike

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