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A thought about LOD

D

Damien Moriarty

Messages
24
G'day all,

This has bugged me for a long time.

With LOD in gmax, if I recall correctly, the value used in the name of your part in gmax eg. model_LOD_100 relates to the size in pixels on the screen. So if you have model_LOD_1000, that model will show when it almost fills full screen in 1024x768 and model_LOD_100 will display until the model fills 100 pixels in the screen.

I have noticed for obvious reasons that different resolutions have sometimes unwanted consequences for which LOD models display. I sometimes wonder why the LOD system values were not based on percentages of the screen resolution being used instead of pixel sizes because you will see you have very different results in 1024x768 and higher resolutions like 1600x1200.

For example, I am using an ultra high detailed apron texture I have just built and I am using LOD to prevent the high resolution texture appearing until after you touchdown and start taxiing (I would rather have a pause taxiing than on finals :) ). So my LOD_1000 apron poly uses the high res texture, LOD_800 uses a Gmax material at present but will have a low res version of my high res texture eventually. It works really well so far.

In 1024x768, it switches models when I intend but in 1600x1200, my high detail apron appears too early on finals. As a result, I am going to include an LOD for each resolution so users can set things up to suit their preferred resolution.

I can live with other models not displaying exactly when I want but for really important things like my apron, it is a bit annoying.
 
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Hi Damien,

First the name does not directly relate to the resolution. You have ten LOD models (between LOD_010 and LOD_100, as far as I now LOD_800 or LOD_1000 will not work).

The way the switch between the LOD models is calculated is rather logical. The switch is determined by the amount of pixels a certain distance needs. So let's say the detailed object is shown when 1 meter of that object needs 10 pixels are more to show.

With a higher resolution it is logical that the higher detail model is shown first, as it will use that amount of pixels earlier. And because it uses more pixels you want to see the detail earlier.

If you want to switch the models independant of the resolution I think you should use a simple distance check, not LOD models.
 
That is interesting, that LOD_800 and LOD_1000 also work. I guess I will have to do some tests and study their code. Maybe we can extend the list made by Rhumbaflappy some time ago with the resolutions of the different LOD models.
 
Hi Damien.

You may be onto something. Perhaps the LOD number does simply refer to the number of pixels required to draw the MDL within the viewport ( horizontally? ). If so, then not only the size of the Window display, but also the zoom level of the viewport will determine which LOD is used.

I seem to remember the SDK for FS9 would allow LOD_200, but I also found it can go much higher.

Distance of the viewer to the object seems to make no difference... but tweaking the ASM code can force distance display.

Dick
 
I could not find anything in the SDK that was over LOD_100 for scenery. Aircraft was expanded from LOD_200 to LOD_400, but then that is a completely different type of model. I used 6 levels up to LOD_100 for an aircraft carrier and it works beautifully but then I first experimented with diffetent colored boxes first to get some idea for where the changes took place and since it is at sea, I set my max distance to as close to 27 miles as possible. Now if your flying down on the deck the ship appears on the horizon very close to the way it would in real life.

Lou
 
Hi Dick,

Interesting idea that the number defines the amount of pixels. The LODs are checked with the vsize command btw, so it would be the amount of pixels in the vertical direction. It is indeed true that the LOD models also depend on the zoom level, but that is logical.

Once I find some time I will do some tests to verify this.
 
Hi!
I find this finding interesting and maybe a little bit dissapointing. If I understand correctly, then if I have a small house with size let's say 10x10m and I use LOD_1000, then I should see the fence on the balcony of the house when I almost hit the house? And if I have a large terminal, let's say 150m x 80m, I can see the fence, when I am let's say 300m away? If this is true, then I can assume LOD_100 for one object is not the same for another object of different size?

Best regards,
 
Hi Goran,

Yes, that is a good observation. I don't think it works like this. There is another thread where Dick posted the values at which the different LOD models change (a certain amount of pixels used by a certain amount of meters) and with my model I tested with these values were the same. As my model will certainly be different from the one Dick used I am rather sure that the switches are made at a certain resolution (pixels used to cover x meters).
 
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