Hi Thorsten,
I think you are on the right track by looking at the tile cache. The
original design used a distance based metric for removing the tiles that are
the furthest away, but somewhere along the way we got talked into switching
this to a time stamp based approach.
Along the way we added some code that could query the ground height at
arbitrary locations, not just the current aircraft location, so this
complicates the whole tile caching scheme because a variety of locations and
tiles could be referenced. I wonder if we somehow get into a situation
where the cache isn't big enough for all the tiles we are trying to
reference? Or some combination with how we reference tiles as stopped
playing nice with the tile cache management scheme?
But I'm pretty sure the tile caching system is the proper place to be
hunting.
Regards,
Curt.
On Sat, Sep 18, 2010 at 5:11 PM, ThorstenB <bre...@gmail.com> wrote:
> On Saturday, September 18, 2010 18:32 Durk Talsma wrote:
> > Given, my observation that cycling through all the viewpoints, will
> restore
> > the visibility of tiles that have gone lost, and flag tiles that were
> visible
> > during the previous view cycle invisible, makes me suspect that something
> in
> > the code that determines tile visibility may go astray after a prolonged
> > number of tile crossings.
>
> Thanks Durk, in fact your observations are very helpful!
> I also noticed that tiles sometimes reappeared - i.e. when I paused
> the sim. But it's not the pausing that helped, but indeed the view
> cycling - specifically cycling through the tower view helps. The tower
> of the home airport is far away when the problems start. The tile
> cache isn't big enough to hold all tiles of two different locations -
> so switching to the home airport and then back causes a reload of
> all/most tiles.
>
> And it's indeed connected to the number of scenery tiles covered by
> the flight as you mentioned - not the distance in the first place. I
> found that I'm not seeing any problems unless the tile cache is filled
> to its maximum. And when I circle in my regular home airport area, the
> cache is not completly filled - and I have no issues.
>
> I'm currently monitoring what's going on in the FG Tile Manager and SG
> tile cache module. The tile cache makes its decision to kick a tile
> from the cache purely based on a timestamp (oldest tile get's kicked).
> This strategy works nicely when flying in a straight line (oldest
> timestamp => tile is furthest away). But not so great when you fly
> sharp turns (oldest tile may still/again be right in front). I suspect
> there is some kind of connection to the problem, e.g bad strategy
> kicks tile in front of plane from the cache, and then this tile does
> not get reloaded. It would explain why I often see issues with a
> disappearing destination airport: you fly (almost) straight from A to
> B - and then, at some VOR, you make a sharp left or right turn to
> line-up for the approach - and soon afterwards I start seeing most
> issues (on short final :-(...).
> Well, just a theory so far. I'll do a bit more digging. Any hints still
> welcome.
>
> cheers,
> Thorsten
>
>
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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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