>>> And increase X until the sphere disappears, on my system X=2e7 doesn't
>>> render.
>>
>>  AFAIK that's not because of precision, but because of an explicit limit
>> in the source code for such things.
> 
> Is the purpose of the explicit limit to hide precision errors becoming 
> visible?
> 
> Why is the limit so low, 2e7 is absolutely tiny compared to the 64-bit 
> floating point range of 1e300 or whatever it is (which presumably POV 
> uses).
> 
> 
If you have a value of about 1e100, then, the last digit presision would 
be about 1e90 to 1e93. This is a serious loss of precision.


Alain

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