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Land Impact and Physics model issue

iFirstLife Newey
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Hi, I'm relatively new to creating meshes, and this might b asked before, so sorry to trouble u :(

The first problem is the land impact my plant model has, its LI is about 11

Screen Shot 2014-05-25 at 5.06.27 pm.png

Yes, I have used "Use LoD above" for medium and below LoDs, as I am unsure on how to create a less detailed model for my creation, which consists of a vase and 6 seperate crooked rectangular stems. I have tried resizing the object to become smaller, but it seemed to make the LI go even higher. Could I have some suggestions on how to decrease this LI at the same time retaining its details even at lower LoDs? (I want my customers to have a product with the least LI ^^)

The second problem is the physics model not attaching properly to the model as can be seen above, when uploading it.

Screen Shot 2014-05-25 at 4.44.17 pm.png

The model on the right is the actual size of the physics model and on the left, the actual model. The physics model seem to only cover the vase (which is a seperate object, not part of the stems) when uploading it. Is there any way to make the physics model cover the whole actual model either in SL or in the 3D modeling software (I use blender 2.70)?

Thank u so much ! :D

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  1. Join everything in Blender so it's one object.
  2. Make a model for the lowest and (possibly) next lowest LOD that is nothing but elongated cubes. No need for that much detail at further distances.
  3. Use the physics model as you have it, it'll work correctly for a single object. Otherwise you'll need a physics model for each separate mesh.

This should reduce your Server weight from 3.50 to 0.50 (each mesh object requires 0.50) and both Physics weight (which is currently driving your LI) and Download weight (which is being driven by the lowest LODs) to less than 1.0.

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On more thing ... your physics shape is presently triangle-based. That means you didn't click "Analyse". Triangle based shapes are bad for small objects. Their physics weight increases the smaller they are. If you click "Analyze" (afyer you have joined the meshes!) that should give you a physics weight of 0.36.

As it stands, each separate blender object is getting its own physics shape. For the stems, those will be expensive hulls, and they all add up. Each is then stretched/dqueezed to fit the bounding box of the corresponding visible object. That's why your provided shape is being squeezed to fit the vase object, and why joining them solves that problem.


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A couple more comments to what has been said (and thank you for the clear and large photos which really helps).


There ARE times when you will need to have an object as a linkset (where you have two or more mesh objects as one mesh - you have a linkset of seven in your example). The most obvious one is when you need to script part of an object. MOST of the time joining things together is one of the last steps as you work. Be sure and save the file BEFORE joining for later LD. Sometimes you will want to upload the parts of a mesh separately.

Oftentimes you can use a plain cube for your physics model -- small items like decor you have here. Physics get more complex when you need to walk through a doorway but for many items they don't matter all that much.

The BIG thing I see in your screenshots is that your are using the same LOD setting for all levels -- a VERY bad plan. This item should easily be .5 land impact when uploaded -- the lowest you can have as the server weight will always be .5 per object.

TESTING is important here to get a feel of what works and doesn't work. The beta grid is the best place as uploads are free. So -- even though this is a low poly mesh -- your high and medium LODS might be the full 244 mesh, but as you move away from the object the count can go down. The lowest LOD is normally the one that entails the highest land impact cost so watch it carefully.


It is also good to test your build using LOD 2 in the viewer as well as LOD 4 which most of us have as standard. The viewer default is LOD 2 so if it looks bad at that setting, then it will look bad for the new folks :D.

BTW when joined, and with that lowest LOD cranked down, your upload fee will be 11 -- a bonus!

Go forth. Have fun. Come back with more questions


 EDIT:  There was a mention of MATERIALS above -- a definition of an area of a mesh that can be changed inworld using SELECT TEXTURE in the buils menu (so like one face of a cube).That would let you put one texture on the twigs and another on the vase -- using regular inworld textures.


You can ALSO easily put all texture areas (islands) on one png - mapping a piece at a time. That of course is a whole nother skill set to work on if you haven't mapped yet.  Just keep that in mind. Mapping lets you use one texture (with ambient shadows which give more depth to the object) for the whole object -- a better use of texture resource download than having to download say four 512 textures for as single build.

I went into my inventory and dug out MY vase with twigs and smiled. One of my first items, it had two materials that took regular SL textures :D.  I was SO very proud of that! 

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LOD 2 in the VIEWER.

We have a choice of how we view items inworld. You know those notecards when sculpties came out?

"how to see your scuplts better" etc?  That was about changing the LOD setting in the viewer to 4. Now (in Firestorm anyway) it is easy to do on a slider bar in quick preferences. The point was that while many folks KNOW to change their LOD viewer level to 4, the default is 2 and so those that do not know (or cannot change because their machine isn't hefty) will be viewing your item at LOD2.

Hope that is clearer.

I also just added some stuff to my previous comment. :D.


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It's RenderVolumeLODFactor which is 1.125 by default for most graphics presets. Not 2. It's only 2.0 by defaullt when graphics is set to Ultra. It is usually controlled via the "Objects" slider in Prefs > Graphics > Mesh Detail. from 0.0 to 2.0.

Third party viewers may have different default settings, for whatever reason.

I always build my meshes so that they will work fine with the default setting of 1.125. Why? Because with mesh I can. And I like to take advantage of the viewers dynamic LOD rendering. Second Life is always overloaded with too many polygons, and too many, too large textures. So it's good advice to keep the RenderVolumeLODFactor as low as possible, no matter how "hefty" your machine is.

About the Analyze button. Clicking it will break up the physics mesh into a set off convex shaped hulls. Which the physics engine reads as hulls, instead of calculating each triangle in the physics mesh against possible collisions. Which makes the calculations much easier on the engine.

Here is a more detailed explanation about collision shapes and the Havok Physics engine.



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Oh ic. Thx! Well I have applied all the tips I've received, but still, I'm unable to get a LI value of 1 D:

Screen Shot 2014-05-25 at 11.51.15 pm.png

I've made different models for each LOD (highest displayed in the img above):

Screen Shot 2014-05-25 at 11.51.19 pm.pngScreen Shot 2014-05-25 at 11.51.23 pm.pngScreen Shot 2014-05-25 at 11.51.27 pm.png

I've also noticed that the size/shape of the vase differs from each of the LODs (especially Medium), even if they are the same in blender. I created totally new stems for each of the LODs, could that be the cause of this problem? What is recommended for me to do from here on? o.O!

Oh and yea I'm trying to get into the habit of testing my meshes with rendervolumeLODfactor of 1.125 now, so that I can better create products which looks great for everyone viewing it ! :D thx for that tip!!

EDIT: Could resizing the object down in blender, help getting a lower LI? thx!

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The lowest LOD level has very strong effect on LI. Your example is very lowpoly, whitch is very good. But the LOD0 triangle count is still 84, whitch is quite a lot in SL (would not be lot somewhere else maybe).


I do not know the exact formula, but maybe you should try to lower the lowest polycount to something like ...20..30. It should bring the LI down even more.

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The different sizes is usually a result from a different size of the objects bounding box, compared to the size in the High LoD meshes. Make sure you have kept the bounding box size of the High LoD, and apply rotation/scale to each of the meshes before exporting.

As a rule of thump (at least my rule), if you want to achieve a LI of 1 (for rather small meshes), you have to bring down the triangle count in your lowest LoD to around 20, or less. Otherwise it's hard to get that  LI of 1.

With your object you could make the lowest LOD out of 4 planes, crossed like a classic tree, with a projected image of your plant vase, on each side of the planes. Pretty easy to do with such an object. You only have to make that on a seperate material, which only shows on the lowest LoD. This will give you 8 triangles in your lowest LoD, plus 1 triangle for each of the other materials you have on that model. You have to carry all the materials through all the LODs. That means, you will have to add one more triangle to the higher LoDs as well, to carry that material from the lowest LoD.

That image on the lowest LoD can be pretty small actually, 128x128 or even 64x64 will look pretty enough. At least that's what I would try.

On the other hand, not everything in SL hast to be1 prim/LI. If such a thing is 2, or 3 LI, it's still fine. People don't do themself any favor if they are cramming thounsands of objects onto tiny spaces, and complaining that SL is such a laggy place.

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You haven't said anything about the size of your object. The download weight, which is dertermining your LI, is very dependent on the size of the rezzed object. If it's very big, then the lowest LOD becomes irrelevant, and so on*. If it isn't scaled properly in Blender, you can scale it on the options tab, where it will tell you the final dimensions.

*There is more detail, possibly too much, about this in this old thread.

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For the least (“lowest”) LOD model, you could delete the the ends of the 6 branches (6 faces on top, and 6 on the bottom; a total of 24 triangles) and the bottom face of the plant, therefore reducing its cost by 26 triangles. The bottom ends of the branches, which are hidden, may be deleted from all the models regardless, including the highest, since they're not visible.


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