Carriers are set to 0 ft altitude. However, we were aware of the discrepancy
caused by a flat sea on a roundish world. The wake of the Nimitz is angled
down to form a skirt that conceals the error from most, if not all, normal
viewing angles. We deliberately do not seek the local sea level as this
would both be expensive in frame rate terms, and the vertical movement would
tend to unlatch aircraft on deck from the carrier.
Vivian
-----Original Message-----
From: Curtis Olson [mailto:[email protected]]
Sent: 25 January 2011 18:13
To: FlightGear developers discussions
Subject: Re: [Flightgear-devel] Carrier Altitude
Quick explanation: the world is curved (oblate spheroid) so if in order to
have an ocean that measures zero MSL at all points, it would have to be
curved. To do this perfectly requires a *lot* of polygons. We have been
using large polygons for the ocean so that leads to some errors depending on
where you are within the polygon. Near the verticies will be pretty
accurate, near the middle could be off by a few meters.
Regards,
Curt.
On Tue, Jan 25, 2011 at 11:57 AM, Peter Brown <[email protected]>
wrote:
In attempting to place an item on the ocean surface, I came to realize that
it's not the Nimitz that is "hovering" above MSL, it's that the "ocean
surface" is about 7 meters below MSL. I was going to suggest simply
dropping the carriers to match, but then looking around I discovered that it
was not constant, as the ocean surface is different from front to back of
the Nimitz.
So the ocean surface is not flat. Where it meets the terrain north of the
Golden Gate Bridge the water is at zero MSL. It then slopes down as it you
head out to sea, to -8.72 meters below sea level, before starting to come
back up again. I did not continue out to see if it continues to rise and
fall, or if it's purely a dip in this area. This is different from the
ocean surface being curved to match the earth, as it actually has a dip, at
least in this spot.
See screenshots -
Terrain intersection north of Golden Gate
[URL=http://s512.photobucket.com/albums/t325/barefootr/?action=view
<http://s512.photobucket.com/albums/t325/barefootr/?action=view¤t=Scre
enshot2011-01-24at102804PM.png%5d%5bIMG%5dhttp://i512.photobucket.com/albums
/t325/barefootr/th_Screenshot2011-01-24at102804PM.png%5b/IMG%5d%5b/URL>
¤t=Screenshot2011-01-24at102804PM.png][IMG]http://i512.photobucket.com
/albums/t325/barefootr/th_Screenshot2011-01-24at102804PM.png[/IMG][/URL]
At the Nimtiz
[URL=http://s512.photobucket.com/albums/t325/barefootr/?action=view
<http://s512.photobucket.com/albums/t325/barefootr/?action=view¤t=Scre
enshot2011-01-24at100253PM.png%5d%5bIMG%5dhttp://i512.photobucket.com/albums
/t325/barefootr/th_Screenshot2011-01-24at100253PM.png%5b/IMG%5d%5b/URL>
¤t=Screenshot2011-01-24at100253PM.png][IMG]http://i512.photobucket.com
/albums/t325/barefootr/th_Screenshot2011-01-24at100253PM.png[/IMG][/URL]
West of Nimitz
[URL=http://s512.photobucket.com/albums/t325/barefootr/?action=view
<http://s512.photobucket.com/albums/t325/barefootr/?action=view¤t=Scre
enshot2011-01-24at103120PM.png%5d%5bIMG%5dhttp://i512.photobucket.com/albums
/t325/barefootr/th_Screenshot2011-01-24at103120PM.png%5b/IMG%5d%5b/URL>
¤t=Screenshot2011-01-24at103120PM.png][IMG]http://i512.photobucket.com
/albums/t325/barefootr/th_Screenshot2011-01-24at103120PM.png[/IMG][/URL]
Anyone know why? Or, more importantly, can we set the carriers at an
altitude appropriate for their default location, so they are no longer
"hovering"? I'd prefer to do it globally so everyone was at the same
altitude.
Thanks,
Peter
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--
Curtis Olson:
http://www.atiak.com - http://aem.umn.edu/~uav/
http://www.flightgear.org - http://www.flightgear.org/blogs/category/curt/
<http://www.flightgear.org/blogs/category/personal/curt/>
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