Re: [Flightgear-devel] Carrier Altitude

Tue, 25 Jan 2011 11:01:13 -0800 

On Jan 25, 2011, at 1:13 PM, Curtis Olson wrote:

> 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.
> 
> 

Curt,
        Does it not seem a bit odd to have a divot like this?  I expected if 
flat then the polys would only go down until the mid-span of the ocean surface 
and then it would rise back up to meet the terrain again. 

Either way, can I suggest we lower the carriers to a closer approximation of 
altitude, at least at their default AI locations?

Thanks,
Peter


> 
> 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&current=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&current=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&current=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/
> 
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