Celestia Forums

Hello, I made a short test.
In some guide for virtual textures I found that the "tile-size" in .ctx files should be set to half of the real tiles so 1024x1024 -> tile-size=512

This has the advantage, that aproaching the surface very slowly the higher level tiles are loaded so early, that the lower level tiles still look sharp.

Now I found that in 16k Mars ( m46shaded jpg from jestr) the tiles are 1024x1024 and in .ctx: tile size = 1024
So I wondered why that ? I think I know now.

I use a 21" Monitor with FOV about 43?° and tried two settings for this VT.
1. tile size = 1024
2. tile size = 512

I tested during a slow (very slow!) centered aproach on mars.
No cloud maps or bump maps.
With "alt Gr ~" I checked which files are loaded during the aproach.

Result:
1. with original setting the higher levels are loaded quite late so that the lower levels already start to unsharpen. In the nearest position there have been loaded 22 files of the highest level (level 3). Works quite fast.

2. with tile size set to half of the tiles no unsharp levels can be seen cause the higher levels are loaded earlier. Looks good but there is one big problem:
In the nearest aproach above the surface there have been loaded 88 tiles of level3 . In this level are only 128 tiles so more then half of all level 3 tiles have been loaded, in fact parts of the back side are among them.

Can anyone explain this to me ? The level3 tiles are definitely loaded when only parts of frontside are viewable so why are so many tiles loaded ?
Does this part of the engine have to be reworked ?

BTW: For handling VT??s it is very uncomfortable that during the loading the keyboard locks the last key so that you almost zoom out of the galaxy when you want to increase distance a bit. I wonder if it would be possible to show place holders for example till the tiles are loaded. (see http://niedersachsen-karte.de )

J?¶rg

guest jo wrote:This has the advantage, that aproaching the surface very slowly the higher level tiles are loaded so early, that the lower level tiles still look sharp.

And the disadvantage of higher memory consumption, eh?

Can anyone explain this to me ? The level3 tiles are definitely loaded when only parts of frontside are viewable so why are so many tiles loaded ?

I can't explain, but I can certainly confirm that it's so. I've been working on a 64K VT frrom the BMNG data, and I tried setting the tilesize to 256 (they're 512x512 in reality), and got the same sort of behavior you describe. I didn't actually count the tiles that were listed in the "console" output, but obviously many more tiles than I was looking at were loaded.

In fact, starting Celestia from my default vantage poing 7000 Km above my home in North Carolina, USA, and zooming to the surface, I found that Celestia was using 541 MB of memory when I got to the surface, if the "TileSize" for each of the loaded textures was set to "256." However, if I set the "TileSize" to "512" the memory usage when I reach the surface is only 377MB. (When Celestia first loads, it takes 109MB.)

Does this part of the engine have to be reworked?

I couldn't say... but it certainly seems to be loading a lot of tiles unnecesarily. I wonder if the idea of setting tilesize to half the real value was intentional on the part of the Celestia devs, or a hack someone came up with along the way. I imagine it was probably the latter, in which case this side effect could not have really been forseen.

you almost zoom out of the galaxy when you want to increase distance a bit.

LOL. I just noticed that for the first time today. I guess because I usually use my mouse wheel for zooming. I was zoonimg in and found my nose was suddenly in the dirt!

Ok, I also in the meantime found out that the mouse works smoother and responds better.
Thanks for confirmation.