Terrain changes with distance

[ahinterl 1]

After installing the 38m Alps mesh and doing some low-and-slow flying around LOWI, I experienced something which wasn't so apparent to me until then, maybe I had this always and never really realized:Though I have most parameters in fs9.cfg maxed out (esp. the terrain_default and _extended radii ones are set to the max value of 10.0) and the max_vertex level is 21, I can see the terrain change while I'm moving along. I.e. during flying, parts of the terrain are re-drawn as closer as I get, it's like mipmaps are exchanged with the distance, in my case the terrain is re-drawn with more precision.Same goes for the ground texture, but that's something I could explain because of the terrain_default and _extended radius settings and the way FS handles the depiction of textures.This way, I'm moving along some kind of "living" landscape, a very strange effect.Something I should worry about ;-) (guess it's normal...) ?Andreas

[Holger 0]

Hi Andreas,interesting observation.In fact, it is your high TMVL setting that is at least partially responsible for what I call terrain "morphing". The FS terrain engine displays terrain mesh data in concentric circles around your aircraft (actually, it's not circles but rather cross-shaped arrangements of rectangular sections), with each circle using less detail. This is similar to mip-mapping in that it avoids using highly detailed data in the mid- or far distance that can't be seen anyway; probably conserves system resources too.Increasing TMVL forces the terrain engine to use a finer resolution in the inner circle, regardless of the resolution of your default or add-on mesh. With TMVL at its default 19 the inner circle uses LOD9 or a 76-m grid spacing, whose display distance ("ring" diameter) is quite far, about 20-25 miles. However, increasing TMVL to 20 reduces that distance to about 15 miles and switching to 21 to only 6-7 miles. Thus, at TMVL=21 you now have three circles of data - LOD11, LOD10, LOD9 - when at TMVL=19 there was only one. Those additional circles require more or leass independent terrain calculations and may actually read from different mesh files (that's a whole other story). Since flying means you're actually moving those rings with you there are constant adjustments at the boundaries between those rings as welll as within the ring areas. Depending on your system's raw power and various parameter settings that "morphing" will be more or less pronounced.For our Alps mesh there's no need to set TMVL to 21 because the mesh itself is compiled at 38-m resolution (=LOD10 or TMVL20) and will also look almost identical at TMVL=19. In fact, TMVL=21 value is known to create problems with the terrain shadows: you're more likely to see straight edges of mountain shadows when they should be jagged.Hope that helps. Cheers,Holger

[John_Cillis 2,406]

Thanks for this Holger--I didn't really know myself what impact the TMVL had on this type of behavior. I am puzzled how your scenery can appear so detailed, yet have zero impact on my fps especially given that I'm crunching it with a P3/800. If anything, my flying through the Alps now seems smoother than any other part of the planet. I spent the entire weekend exploring the Alps. How good is your scenery?During my teens and 20's, I crisscrossed the Alps during many trips to Germany, Switzerland and Austria. I can "fly" through your mesh and fly treetop level, and recognize canyons and mountain passes I've traveled through and navigate anywhere I want just by memory alone. It's absolutely amazing the amount of beauty you've added to this region of the world! Thanks aren

[Guest UlfB]

Yeah, :-)Thanks Holger for a very straight forward explanation.Ulf B

[Guest stevehow]

excellent explanation...at last someone i can understand.. thanks steve

[Mace 1,927]

HolgerI don't know exactly what Jonathan di Ferranti's data was, but your Alpenmesh is great. It also brings back memories for me of flying in the Bernese Oberland. I probably don't know as many valleys as John, but I do know the Interlaken area and yours is the best rendition I've seen yet. I know those peaks there and they are as impressive in that mesh as they are in real life. At any rate you should thank again Mr. J. di Ferranti.I always kept my TMVL at 21, because I wanted to be ready for any hi-res mesh that I might have (such as 19m etc.). I have never heard before that TMVL=21 might be somehow bad. I will keep it on 20 unless and until I need 21, which I don't think is needed for say, the FS default Grand Canyon mesh.Now if I can just add in some of cable cars to the Schilthorn I'll be in like flynn...Rhett