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Thread: Question re LOD (Level of Detail)

  1. #1
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    Default Question re LOD (Level of Detail)

    What I find annoying is to have some trees that have different LODs than other trees. Also, I have had to remove trees from my route that I downloaded from the DLS which were just what I wanted, except the 2nd level of LOD was unacceptably close in.

    Question - at the current state of computer hardware, are we not yet at (or close to) the point where LOD is just not necessary to have good performance of our routes?

  2. #2
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    LOD is required due to the computer's ability to process the amount of data. This has nothing to do with Trainz; it's just a lot of unnecessary data using up resources that are best used by other things. If you have your tree, for example, with 14,000 polygons on its mesh, why would you want to still load up all 14,000 polygons when the asset is located 10 miles away when you only see something about the size of a pixel? The resources needed by any computer or any program, for that matter, will cause a slide show. In the example of your single tree, try multiplying this by several 1,000s and your computer will stutter and stall.

    The problem you are seeing with this particular tree is a poor implementation of LOD. There's a recommended breakpoint and asset size where the next target is supposed to replace the current asset. If the content creator did not follow those rules, you'll end up with the issue you are having.

    Anyway, LOD is used in other graphics intensive programs including Cities Skylines, Arma3 and others just thinking off the top of my head. How the LOD is implemented and how well the content creators follow the rules determines not only the quality of the breakpoints, but also the performance of the assets in game.
    John
    Trainz User Since: 12-2003
    Trainz User ID: 124863
    TS12 Build: 61388
    T:ANE Build: 90955

  3. #3
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    Quote Originally Posted by schweitzerdude View Post
    What I find annoying is to have some trees that have different LODs than other trees. Also, I have had to remove trees from my route that I downloaded from the DLS which were just what I wanted, except the 2nd level of LOD was unacceptably close in.

    Question - at the current state of computer hardware, are we not yet at (or close to) the point where LOD is just not necessary to have good performance of our routes?
    Take a closer look at the LOD you maybe able to configure it to change when you want to. It should be in the config.txt file. If you're lucky it will have an lm.txt file just drop the numbers at which each LOD kicks in.

    Cheerio John

  4. #4
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    Thanks to both Johns.

    I will try to find those trees again and play with the settings in the config.txt file.

    So let me ask this question: Is it accurate to say that if you can easily detect the change in LOD for a given asset, then LOD was not correctly implemented for that asset?
    Last edited by schweitzerdude; October 22nd, 2018 at 03:49 PM.

  5. #5

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    Quote Originally Posted by schweitzerdude View Post
    So let me ask this question: Is it accurate to say that if you can easily detect the change in LOD for a given asset, then LOD was not correctly implemented for that asset?
    Yes, with some conditions. LOD can be made undetectable by making the change at a large enough distance, but that defeats the purpose. The trick is to keep the distance as small as possible while also concealing the change. But there are some things that work against concealing the change. For instance, if the surface is reflective (like many traincars) then the apparent angle of that surface affects the image. If that angle changes the image will change. Simplifying the mesh necessarily requires changing the angle of at least part of the surface. So it might be very difficult to simplify the mesh and keep the image the same, even when detail is minimal. This is an effect you often see on track, where the mesh for the sleepers is flattened, removing the vertical surfaces and significantly changing the appearance even when the same textures are used (and viewing at a low angle exaggerates the effect). It's a compromise, and can be very difficult to tweak effectively or in all viewing conditions.

  6. #6
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    TRS19 introduces some new LOD control options that can be used for scenery objects that provide better control over LOD change distances. Previously, only the LM.TXT method and the spline hi/lo path options gave the creator any control. The older mesh table LOD gave the creator no control whatsoever and it was very evident on very large objects such as buildings.

    Some creators are starting to use better methods to fabricate textures that look more realistic on lower poly meshes. These include very high poly meshes that are not used in game but are used to bake normal and AO maps for the lower poly models.

    Paul


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