On 11/29/2016 5:04 PM, Mike Horvath wrote:
> On 11/29/2016 3:26 PM, clipka wrote:
>> Luminance gets a bit more complicated: You have to use an atan-based
>> formula to get an angle, but you must plug in the y coordinate and the
>> distance between the y axis; the latter is equal to sqrt(x*x+z*z), so
>> this gives you:
>>
>>     #declare fL = function(x,y,z) { atan2(sqrt(x*x+z*z),y)*CONST }
>>
>> Choose CONST values as needed; atan2()*CONST may happen to be replacable
>> by atan2d() again.
>>
>
> Wikipedia says it should be more like
>
>     #declare fL = function(x,y,z) { atan2(sqrt(x*x+y*y+z*z),y)*CONST }
>
> Do you agree?
>
> Mike

Wait! I scanned your response too quickly. Wikipedia gives this:

	acos(y/r)

which is totally different from what you suggest. Are they equivalent?

Mike

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