Hi,
My question has to do with the Back-to-Front clip plane distance ratio
which is
recommened as being 3000 (although it can be more but with degredation).
Take the case of a Solar System simulation where we have an Earth centered
system
containing an orbiting vehicle and the Moon.
Earth Radius = ~ 6,400,000 m
Vehicle altitude above earth = ~ 400,000 m
Moon, Distance to Earth = ~ 380,000,000 m
Say I have a vehicle which is orbiting around the earth and I am using a
camera to
follow this vehicle. Say the altitude is 400,000 m (400km...low earth
orbit)
...IF I want to be able to have a 1 m resolution (1 m front clip distance)
and still
be able to see the earth below then I have to have a back clip distance of
at least
400,000 ... which means the ratio is 400,000!!!!! This is 100+ times what
the recommended
ratio of 3000.
Even worse, if I am following this vehicle as it orbits the moon and want to
keep the
1 m distance from the vehicle and still see the earth (maybe see an Earth
Rise) then the ratio
is 380,000,000 to 1 .... WAY ABOVE the 3000 recommended.
SO, my problem is that I want to be able to have the ability to zoom close
to a vehicle
and still be able to see earth below it....and more importantly be able to
see other vehicles
that are going to rendezvous with mine but are far away...more than 3000 m
away.
For the most part, going higher than 3000 is ok for some things, but in
other cases that
I've come across, if I go above a ratio of 50,000 I get merging of
geometries...ie, I see
things behind the earth that should not be visible.
Please give me suggestions to overcome this problem? ... should I be using a
different
"policy" for the back/front clip planes? Oh, and, explain it to me as if I
was a 3 year old
so I can easily implement it.
Thank you for your help,
Mario
Mariusz Zaczek
NASA - Johnson Space Center
Automated Vehicles and Orbit Analysis / DM35
Flight Design and Dynamics Division
Mission Operations Directorate
Bldg: 30A Room: 3040A
Disclaimer: "The opinions, observations and comments expressed in my email
are strictly my own and do not necessarily reflect those of
NASA."
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