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Mesh Landscapes: Quirks & Oddities


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I've been experimenting lately with the idea of creating an entire sim in a CAD program (3DS Max in my case) and importing it into SL. However my tinkering has turned up a couple of weird issues that I was hoping to get clarification on.

 

Firstly: Mesh size restrictions.

http://puu.sh/mQj0u/f2488ede03.jpg

The image above shows my landscape as it is in 3DS Max. It's seperated into 16, 64m^2 segments, with varying height. Each segment has 2048 tris, for a total of 32,780 tris for the entire thing. However, when attempting to upload to SL, it seems to hard-cap it at 240m^2 (which I cannot change), as seen here.

http://puu.sh/mQjqz/2aa3dcff19.jpg

All the segments are definitely no larger than 64m^2 in size, so it's not an issue of my creation. Is anyone else aware of this limit? If so, why is it there and is it possible to bypass? As you can see in the image below, taking off the outer segments (to reduce the max size to 192m^2) allows me to upload it at full size.

http://puu.sh/mQjvL/2512644511.png

 

Secondly: Land Impact

Let's take a look at the Land Impact of my landscape (a single segment of 64m^2 for this). I've set the Physics to follow the "High" mesh, so that avatars can accurately walk on the mesh's surface. The image below shows the mesh's LI at full-size (64m^2), with two different physics settings.

http://puu.sh/mQkja/8d06e9f4a5.png Convex Hull, 67 LI.

http://puu.sh/mQkkj/74e53d6281.png Prim, 118 LI.

And here it is, shrunken to x0.25 (16m^2) original.

http://puu.sh/mQkme/4de296085e.png Convex Hull, 25 LI.

http://puu.sh/mQknh/e0af0f1953.png Prim, 494 LI. (!!!)

The smaller I shrink the mesh from the original size, the more LI is impacted when set to Prim physical type. Here it is at x0.15 size.

http://puu.sh/mQkro/5eff9412aa.png Eight hundred and FIFTY Land Impact.

So what exactly is going on here? How come, when Prim physics is enabled, the LI is reasonable when scaled to maximum size, but gets ridiculous when shrunk?

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"How come, when Prim physics is enabled, the LI is reasonable when scaled to maximum size, but gets ridiculous when shrunk?"

This is expected behaviour for mesh with triangle-based physics where the LI is the physics weight (i.e. when that is higher than the download weight). The physics engine has to do much more work if it has to consider collisions with many small triangles within the collision range of the potentially colliding object, than it does with a few large triangles in the case of the unshrunken mesh. So the physics weight calculation takes account of the size of triangles accordingly.

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That´s interesting. I'm planning to do a sim-size mesh landscape and cityscape in blender, if I can find enough time, but thought probably the size and LI would be troubling.

For a reference - I have a bought mesh landscape, which exists in 3 size versions, comes in parts/with a rezzer, the listed prims are:

256x256 : 106 prims

128x128  : 77 prims

     64x64 : 61 prims

 

(The listings say prims, not LI, I don´t remember if the LI was the same, but I think at least it was similar, don´t have the place to rez that kind of stuff anymore)

 

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The size clamped at 240 meters is definitely a bug introduced with the recent Importer code changes. I have uploaded 256x256 terrain meshes before. Those also did not have the maximum size of 256m x 256m, but they were something like 255.4 or something like that.

I have seen the 240 meters number before, a year ago with multi mesh collada files, when the importer code was under development, where the objects have been set 240 meters apart, when they were positioned very close together actually. My issue has been fixed though, but obviously they left in that 240 meters limit somehow.

You should file a BUG jira about this!

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The key to getting low LI for walkable landscapes is to use larger triangles where you can. You can see the effect in simple 64x64m planes with squares of 1, 2, 4 and 8m sides. Their download/physics weights are 189/232, 47/29, 11,4, 2,0.5. For comparison, The SL land has squares of 1m, like the first of these. That would use 232 of the 937 prims available from the 64x64 area it occupies, about 25%. The picture here shows a 64x64 riverbed mesh. The smallest squares are 2x2m, in the river channel. The flat areas have much larger triangles. It has download weight 23.5 and physics weight 18.2; LI=23.



Mesh this size are always seen as the high LOD (except with perverse viewer settings) and you get no savings of LI at all by using lower detail LOD meshes. It's worth noting that it is possible to accidentally penetrate a triangle-based mesh landscape and get stuck underneath. So either provide a way out from underneath, or make sure your visitors know how to sit on something above ground to get out.

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Thanks. I have added a comment and a simple test file to it.

You should enter a Linden Lab viewer in the Environment field, because the Lab does not fix anything that isn't reproducable on their own viewer. Hence, if you enter a third party viewer, they may not care to try to repro it.

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I made a rough test mesh terrain in blender and uploaded it to a 2x2 sim sized open sim region I share with a friend no problem, see above, and it shows 265x256x80 size and 1 LI lol so I guessed that doesn´t tell me much.

 



Logged into Aditi then and the numbers the uploader told me looked very different. 5202 triangles, 2.240 physics, LI of 229.937 -_- and upload fee of 65 L$, textures and physics included. Is the triangle count the bigger problem or the physics? I´d like the terrain to be exactly walkable.

Unfortunately I couldn´t test-upload it at all, as it told me on two accounts, and I´m sure I did upload mesh on Aditi before with at least one of them, I don´t have the right to upload mesh. The link given to the Aditi mesh quiz takes me to this: I ignored the warning and clicked go, but the page never loaded. From reading on the forum, that seems a common problem.



I´ll keep trying though. Is there a sandbox in Agni, where it would be possible and not rude to uplad a full-size sim landscape, would be maximum 64x64 anyhow I guess, but anyway?

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To make the landscape accurately walkable, you need to use a triangle-based shape (i.e. Not analysed) using the high LOD mesh on the physics tab. Then you have to set the physics shape type to "Prim" inworld. The physics weight reported by the uploader is irrelevant. It's for the default convex hull shape which will not be walkable. Unfortunately you can't see the Prim type physics weight until you have rezzed it inworld. For a 64x64 mesh, only the high LOD counts, so there is no point in making lower LODs. Your mesh appears to have 5000+ triangles,and that accounts for the high download weight, which will be equal to or less than the LI. With that many, consequently small triangles, you are bound to have a high physics weight too, most likely higher than the download weight, which may increase the LI further. The example I showed above, LI=23, has only 504 triangles.

Just to emphasize what Arton said, you can't upload a mesh with any dimension greater than (just under) 64m. If you do, any such domensions will be squashed down to (just under) 64m. If you want to upload something larger, you have to break it into a set of meshes each within that size limit. Although the uploader will annoyingly squash any 64x64 mesh a tiny bit, you can readjust it to exactly 64x64 inworld (I think).

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Thanks for your replies, Drongle and Arton. 

I thought the Analyze was imperative, good to know.

From knowing I can´t build larger than 64 structures without using megaprims, and the opening post I´d assumed I´d have to upload the terrain in pieces already, but as it worked full size in open sim I briefly had the hope that might be a new thing that works in SL too and I just had missed the good news. 256 seems to be the 64 of open sim, I tried and I can stretch a prim to 256x256 there too.

The landscape on my pic is based on a heightmap of a RL existing terrain, so I´ll see how far I can get now with limiting the triangle count. I think 100 LI would be acceptable for my purposes, so based on your example I´ll try to get it down to ~2000 triangles with an estimated LI of ~100 before uploading it to SL.

One of the things I want to make in the end is a comparably detailed volcanic landscape for a friend, and that will have to be in SL, so I´ll have to worry about uploading in chunks and LI, either way.

 

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