On 12/22/06, Dene <[EMAIL PROTECTED]> wrote:
Having been involved with this project I think that part of Arnt's
original post is fuelled by the difficulty in turning TaxiDraw output
into something that can be used by FGFS. While open to the idea of
associated data regarding periods of validity for various layouts, maybe
the underlying issue can be addressed more effectively by an easier way
to convert modified apt data to the required btg data...
This is a difficult issue.
this I gather is
currently done by TerraGear.
Yes, terragear turns the apt.dat information into a 3d model and cuts it
into the surrounding terrain.
Then it is up to the user to decide which
layout they want to encounter. This of course raises issues with
Muliplayer.... as each player should be looking at the same version of
the scenery....
This is an issue in any multiplayer system, and there are tons of pitfalls.
Different players could be looking at different versions of the scenery
database. With LOD, one player could think they are hiding behind a big
rock, but other players might have that rock culled out because it is too
far away, letting them easily see something that should be hiding. And then
if we ever want to start mixing it up with other simulations (X-Plane, MSFS,
etc.) then things get orders of magnitude more difficult because they
probably don't put their runways at exactly the same places, terrain and
surface elevations could vary wildly, etc.
An honest question here though... can TerraGear be
limited to a single tile? IE point it to a tile or ICAO and it will
regenerate just that area...
Yes ... sort of ...
I suspect the answer might be NO for a
number of reasons... if the airport crosses tile boundaries problems
could arise... and ... how would it process tile edges without examining
adjacent tiles....but then I suppose the question is; how will a
different/alternative/appended data format solve these issues?
Any time you touch a tile, you have to take into consideration the cascading
effects of that change. An airport could touch up to 4 tiles (if it
straddles a corner.) Each edge and corner point is owned by one and only
one tile. This is "first come, first serve" when creating tiles for the
first time. So if a new tile is being generated, it must honor and mesh
with any existing edges or corners it matches up with.
It would be interesting to create something like "make" for tile
regeneration ... which would rebuild any tile and regenerate any thing that
depends on it down stream, but I haven't gotten that far.
X-Plane generates the airports on the fly from the apt.dat file, but it's
airport surfaces aren't nearly as sophisticated as flightgear's, and with
our irregular triangle soup approach to modeling the terrain surface, it's
not trivial to cut an airport in on the fly ...
How can code be written when an approach is yet to be decided?
Well here is the current approach.
You can just regenerate your airport and be done, if you don't mind living
with any edge matching problems that might arise from changing the outline
of the airport area.
But to do it right, you have to regenerate the entire tile and any other
tiles that might have edge/corner dependencies (with possible cascading
effects.)
Regards,
Curt.
--
Curtis Olson - University of Minnesota - FlightGear Project
http://baron.flightgear.org/~curt/ http://www.humanfirst.umn.edu/
http://www.flightgear.org
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