Land Impact frustration

[KeistasZmogelis]

Hey there.
I've modelled a Gazebo.
Because of all the details, the triangle count is ~47k.
When importing to SL, the land impact is HUGE, like 300+.
In fact, I have trouble getting the land impact to a reasonable number for any object I've ever made... From a tiny jar, to a gazebo...

I've seen plenty of objects in SL that are far more detailed than any of my models (I try to keep the polycount as low as possible without looking ugly), but their land impact is 1-5... How did they achieve this?
What's the secret here?

What I've tried so far:
1) Make LOD generate with less triangles. So that lets me lower the Land impact to about 100.
2) Simplify the physics mesh by importing simple blocks for collision. That barely helps.
What else is there to try?

One thing i've tested: If i import a simple sphere that is ~45k polygons, it's easy to get the land impact to "1". The only conclusion I can draw from that is that the polygons have to be connected to one another to reduce the land impact. That is, have no separate model parts for the object. How does that make any sense? If I connected all the loose parts, the polycount will jump up significantly. Also, I've seen plenty of objects in SL that are not only hightly detailed, but their loose parts are not connected either, yet, their land impact is still 1-5.

What am I missing? Any suggestions?


[Drongle McMahon]

First: If you have any material with more than 21844 triangles, you are likely to run into texturing problems because the uploader secretly adds new materials. You will save yourself trouble by using multiple materials each with less than 21844 triangles.

Second: There are limits to what the automatic LOD generator can achieve, especially with complex meshes like this. It will often fail to reach the levels of decimation you set with the triangle counts. You will always do much better and have LODs that look better if you make your own LOD meshes.

Third: For this kind of object, the only technique that will get you a low LI is to use a "billboard" method at the lowest LOD(s). This means using a simple very mesh with am alpha texture that's a picture of the ironwork (see below). If you use this for the lowest two ODs, you can get very low LI.

Fourth: You can see when it's the download weight and when it's the physics weight that's keeping your LI high by clicking the "More Info" link in the edit dialog. Whichever is higher will become the LI. For this gazebo to be one you can walk into, you will need to provide a very simple physics shape. See this recent thread for discussion of a similar case.

 

 

[KeistasZmogelis]

First: Different materials with the same data, is it?
Wow, SL is ridiculously backwards in memory saving...

Second: I've tried uploading Simple blocky shapes (That I would have used for physics) as a test for lower LOD levels. 
The impact sky rocketed to 3910+. 
Also, the triangle counts on the importer show "N/A" either on the lower details or the highest model, depending on which I loaded last. What the hell is going on?
I do get a green tick on everything and "Ship it!" though.

Third: Will do, when I find out what the problem is with Second point.

Fourth: I explained that I tried that. I upload a physics model, that is a simple blocky shape, but that doesn't help. The physics are ~10 though. That's better than 3000

[Drongle McMahon]

"Different materials with the same data, is it?"

Don't think I understand what you are saying here. The materials define the "faces" in SL, That is, the surfaces that you can apply different textures to. The reason for this (and some other) limits is the nature of the internal data format which uses 16-bit values (apparently) for some indices. If you want to see more detail about this one, you can look at jira BUG-1001.

"The impact sky rocketed to 3910+."

Again. I can't comment usefully without more information. Have you gone on and uploaded?* Some errors only get detected then. There is a problem if your high LOD has > 21844 triangles and the lower ones then don't have the extra material the uploader generates, but that usually gives an error message and blocks the upload.

*if not, can I assume you aren't getting confused by non-european number format : 3.456,00 vs 3,456.00.

 

 

[Pamela Galli]

See this current thread re impact of joining before uploading: https://community.secondlife.com/t5/Mesh/Land-Impact-individual-vs-linked-upload/m-p/2964183#U2964183

 

I don't know any way to make that gazebo reasonable LI and LOD, without changing the design.  

[Jenni Darkwatch]

I'd split it into smaller meshes: The railings are repeats of each other anyway. Roof part another. Upload them separately. For the railing parts you can get away with simple box physics, for the roof part you could possibly too, or a pyramid even.

Beyond that... yes, use distant impostors for the lower LODs (textures with the ironwork on a flat surface). IMO it should only have this model on highest LOD, everything below almost HAS to be an impostor.

Depending on size, the LI for this might end up still relatively high. But well below 50, IMO.

[ChinRey]

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KeistasZmogelis wrote:

Hey there.

I've modelled a Gazebo.

Because of all the details, the triangle count is ~47k.

When importing to SL, the land impact is HUGE, like 300+.

In fact, I have trouble getting the land impact to a reasonable number for any object I've ever made... From a tiny jar, to a gazebo...

 

 

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Oh, there are sooo many tricks and techniques!

Drongle already mentioned the most important one: don't even think about using LOD models generated by the uploader if you want both decent LOD and low LI. Here are a few others:

1. Balance the weights. Land impact is the highest of three weights: download, physics and server. To reduce LI you need to do something about the highest of them. More specifically: splitting a complex mesh into separate parts will increase server weight but usually reduce download weight. So if download weight is considerably higher than server weight (I'm willing to bet good Lindens it is in this case), try to split it up into several meshes, if it's the other way round, try combining into fewer parts. (Btw, since you mentioned changing the physics model - that's the one that determines the physics weight so it's easy to see if that's the problem - I can't imagine it is in this case though.)
2. Do not mix big and small triangles in the same mesh. Unless you know what' you're doing that is. The two most important factor for determining a mesh' download weight is its overall size and its number of triangles. A mesh with a few large ones will have a large overall size while several smaller ones add to the poly count so you end up with the worst of both.
3. Use smooth normals for all they're worth. It's amazing how many polys you can save that way without ruining the look of your build.
4. Browse through the old posts in this forum. Lots and lots of more hints and tips to be found here.

[Drongle McMahon]

"I'd split it into smaller meshes"

I would have thought this not such a good idea, because of un-coordinated LOD switching. However, I had a go at making a similar pergola in one piece. It turned out that the wrought squiggles were small enough that they degraded quite badly before the first LOD switch, simply because there weren't enough pixels. So it would have been better for them to switch earlier (eg to alpha panels). That would only happen if they were smaller sub-models. So I end up agreeing with you.

"everything below (highest LOD) almost HAS to be an impostor"

Again I agree. That does seem to be the only way to overcome ugly effects because of detail too small to render. I ended up with 102,000 triangles in the highest LOD (lots of exta geometry to get rounded corner highlights but flat sides), then "impostors" at all the remainig LODs. The LI of that was 33. The same high LOD with autoLODs had LI 472, and it looked worse. I have mode some pictures that I might add below. I should go back and split it into smaller meshes as you prescribe above. Not sure I have the time though. I think the best thig would be to have the squiggles replaced by impostors at the first switch, on smaller mesh parts, then to have the main framework all one piece and not becoming alpha until the second switch.

 

[ChinRey]

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Drongle McMahon wrote:

I would have thought this not such a good idea, because of un-coordinated LOD switching.

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Un-coordinated LOD switching can actually be an advantage if you get it right since it can smooth out the transitions between the LOD levels. Although I haven't checked this, it is also likely that spreding out the LOD switches will reduce the item's actual load both on server and client considerably.

And of course, making something like this as a single mesh will increase the land impact. I'm impressed you managed to get it as low as 33 but with some well chosen splits, it should go down to 20 - possibly as low as 10