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Understanding: LOD | The Metaverse Tribune
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Editorial: Understanding: LOD

by Mister Acacia
Published December 13, 2012

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This is third in a multipart series I think might help Second Life users, indeed all metaverse citizens, better understand some of the inner workings and underpinnings of their viewers, the connection to the servers and the servers themselves. In this part, I will talk about LOD, or Level Of Details, and what it really means.

LOD, as shown in the viewer is actually a factor in a complex algorithm that determines how to render complex objects, namely sculpted prims and mesh. In real life, moving close to an object reveals details, and moving away reveals a lesser-defined but still properly formed object. In the virtual world, rendering of objects is mathematical, and there is finite precision. Moving too far away from a scuplted object can make it appear malformed. Unfortunately, this is usually the result of a poorly designed sculpt.

If you take a ping pong ball and just look at it, what do you see? A sphere with a virtually infinite number of surface points. And to recreate that sphere in SL would require a massively powerful computer and lots of time. So as a compromise, sculpts use up to 1024 points to describe the shape of the object, making a sort-of mesh, and the texture “skins” that mesh. And as you move your camera away from the object, the viewer removes a little of the detail, just as you would moving away from an object in real life.

The problem with sculpts that malform at a distance is with how it was initially made. With LOD set to 1, moving your camera away causes the the viewer to use only one in four points. If the creator made sure that every fourth point was used to describe the basic shape, then the object would not change much, or even at all. But not every creator does, as you can see in the image just above. It’s the same sphere as the first one, just rendered with a lower LOD.

To try to offset malformation the viewers include an adjustable value for the formula called Level Of Detail (LOD) factor. Properly crafted sculpts should look about the same at any distance with LOD set to 1. Setting LOD higher causes the viewer to look for additional points. For example, if the LOD is set to 1 and the camera is moved, as soon as it malforms, you could adjust your LOD to 2, effectively telling the viewer to use two of every four points. LOD of 3 and 4 do the same thing, asking for three or four points out of every four. Of course, this also means the viewer is processing more information, so it could present fewer frames per second.

Something that some creators have advised is to set LOD to 5, 8, even 20. But since the maximum number of points you can use, out of four, is four, higher LOD settings cause additional lag as the viewer tries to pull data that isn’t there.

In most V3-based viewers, LOD is in Preferences on the Graphics tab.

Click the Advance button at the bottom and then look for the Objects slider in the Mesh Section. As you raise the slider, the relative size will show on the right side – Low, Med, High.

The Firestorm viewer has this slider in its Quick Preferences, accessible from a button on the toolbar.

In the next part of this series I’ll talk about the care and feeding of the viewer cache, including how often it should be cleared.

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  • http://modemworld.wordpress.com/2014/02/17/feb-15th-firestorm-qa-video-and-transcript-next-release-and-news/ Feb 15th Firestorm Q&A video and transcript: next release and news | Living in the Modem World

    [...] An editorial  on understanding LOD – from the Metaverse Tribune [...]

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