Le 2010-10-14 15:57, Le_Forgeron a écrit :
> Le 14/10/2010 21:12, Florin Andrei nous fit lire :
>> Darren New<dne### [at] sanrrcom>  wrote:
>
>> I think my message was misleading - when I said "zoom in" I wasn't thinking of
>> doing an animation. I'm only interested in the final static view, standing on
>> the surface of the ring.
>>
>> It does seem to be some sort of precision limit or error, indeed.

It is a floating point precision limit. To render that corectly, you'd 
need quad- or higher precision, but your FPU is limited to double.
Others have used a plane to replace the missing fore ground part.

>
> I should try... but I noticed that you used a single cylinder in your
> scene. Does it change anything if you use instead a CSG of 2 cylinders,
> so that the actual ring is more than a foil ?
> (in fact, you would need more to make the walls)
>
> Given the usual range&  precision, I wonder if one unit = 100km would
> not be better ?
> (that make the view point about 0.00002 away)
> Also a caveat: if the<0,0,0>  is the sun, you gonna have problem to
> stand on the ring.
> You might better enjoy having your feet as<0,0,0>, translating your
> ring to match.

The problem is not the absolute value given to an unit, it's de range 
between the largest values and the smaller ones used.

>
> And I never get the "artificial gravity" by rotating: centrifugal force
> does not exist (it's a pseudo force), and I believe the gravity
> direction might not be fully centrifugal: the coriolis effect would
> slant it a bit away from the center

The effective gravity of the Ring world on the surface is exactly zero, 
but the sun's gravity is not and tend to pull everything UP. The 
perceived gravity comes from it's rotation and the "centrifugal" force 
must overcome the sun's gravity.
Now, centrifugal force in a perceived force relative to an object moving 
on a circular path.

The coriolis effect is minuscule here on earth and only works at large 
scale over periods of many hours and days, it is not effective under the 
tropics, and is maximum at the poles.
On the ring world, given the dimentions and the relative thickness of 
the athmosphere, it would be absolutely negligeable, and would only 
cause cylindrical systems parallel to the ground. It would have 
absolutely NO effect on gravity.
What CAN affect the direction of gravity is Relativity and the time 
gravity take to come from the sun compared to the ring's rotation. That 
exact same effect will also slightly shift the apparent sun's position 
away from perfectly over you.

Given the scale and proportions, it's very acurate to represent the Ring 
world as the surface of an open cylinder. At less than a Km thickness 
compared to over 100 000 000Km radius, there is practicaly no diference.



Alain

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