Uploading mesh: does the calculated physics weight even mean anything?

[Vulpinus]

I've noticed before that when I set my uploaded mesh to prim physics, the physics weight goes up to more than the uploader said it was, but it's not been a problem until now.

My latest object went from 4 LI to 13 LI when set to Prim. The uploader calculated the physics for the carefully minimised physics model I made at 0.8.

I knew not to believe that from previous experience, but how on Earth can I know what it really is without uploading the object?

What's the point of that seemingly fictitious and useless number?

For what it's worth: the 13 was with an un-analysed model; it's mostly because of a concave staircase. If I analysed the model in the uploader then it dropped to only 9 when set to prim, but the physics was too far off. Mine was perfect. And it's still too high when the prim linkset I'm replacing is only 8 LI.

 

[Drongle McMahon]

The physics weight shown by the uploader is only for the default convex hull, which is used when the physics shape type is Convex Hull. It is indeed most frustrating that the Prim physics weight can only be obtained after uploading the mesh. There doesn't seem to be any good reason, as the weights are (now) all calculated by the server anyway. So the mesh has to be sent for that anyway. There has been at least one jira sking for inclusion of the Prim physics weight, that has been ignored for years. I am afraid there is no way round this. It is especially frustrating because of the idiosyncracies of the physics weight calculations, which do not operate in the manner described in the wiki, and which, in the case of triangle-based (not analyzed) shapes, are bizzare and unpredicatble. The only way to test Prim physics weights without paying the upload fee is to upload on the beta test grid, Aditi.

 

[Vulpinus]

Hmm... that's about what I guessed. If I thought it would do any good I would go and add my name to the Jira. At least it's free on Aditi, although I'm watching my free money quickly dwindling.

Yeah, I've found the physics particularly unpredictable. Sometimes analysing +/- simplifying produces a better result all round, sometimes it messes up the physics compared to my model, and sometimes my model works out best for LI and physics.

I've just simplified my physics model even more (as much as I can tolerate on the steps - it's not 'good') and got it down to 6 LI. I can live with that, although I might link it to prims like I did with the original linkset for the physics which will keep it at 4 LI I think. I don't so much mind the physics LI itself, it is what it is, just the uncertainty and time it takes to test the unpredicatable options.

[Drongle McMahon]

"watching my free money quickly dwindling"

You used to be able to get more just by asking for it, but I don't know which Linden is there to ask any more.

[Aquila Kytori]

Hi

Here is a link to an old thread where I did some experiments to reduce the Physics cost of stairs and still have accurate physics.

https://community.secondlife.com/t5/Mesh/Problem-with-home-mesh/m-p/1788825#M18558

 

but the more usual way is to use "ramps", and generally ramps and side panels for the handrails are good enough for most stairways

 

[Vulpinus]

That looks interesting, thank you. I'll certainly try those ideas out in my experiments. I have my main staircase replacement on the to-do list. I had figured out that small triangles were not good.

The steps I did are quite wide (6m) and concave. Trying to keep 'true' physics gave silly-high numbers (no surprise) so I went to a concave ramp (inside of a hollow cone section, like I used as a hidden prim originally so I could set the steps no-physics in the convex hull linkset). I ended up with just three segments though to get the 6 LI. Just about liveable with on both counts.

Anyway, so far the meshification of my DIY prim house has saved me about 150 LI, so it's going well.

[ChinRey]

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Vulpinus wrote:

I knew not to believe that from previous experience, but how on Earth can I know what it really is without uploading the object?

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With triangle based physics you can't really. That's what we have the beta grid for.

My personal record is more than 30 test uploads before I managed to find a usable phsyics shape. Somewhere on this forum there is a a picture of them all...