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Problem With Land Impact Of Mesh Creation


Elinah Iredell
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Hi I have some full perm mesh forms I wanted to merge to create something new . I also want my name as creator so that means rezzing a prim cube that I add on as the root prim. Before I add  the prim cube the land impact of the linked mesh creation is 2  and that is fine . The problem is the land impact increases  to 3 whenever I try to add the prim cube . I had thought that when you add the cube to a mesh creation to be able to have your name show up as creator it was not supposed to affect the land impact at all, but for some reason this time it is. What do I do ?

Edited by Elinah Iredell
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8 hours ago, Pamela Galli said:

I don't think there is much to do if three is what you get when you add and round the LI of all the pieces as they are. Cube LI counts like anything else. 

Thank you for your reply. Why is it that sometimes when you add the cube prim to become the creator it does not seem to add any land impact,but  then other times like now the land impact does increase?

Edited by Elinah Iredell
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A more detailed explanation - sorry but this actually is a little bit complicated. But read it carefully and it should make sense ... or just ignore it if you like. ;)

 

An object in Second Life is asigned four weights:

  • Server weight is how much work it is for the assets server (that's the one that stores all our items) to find the item. It is always 0.5 for each mesh, sculpt and prim - plus a little bit if there are any scripts.
  • Physics weight is a wild guesstimate of how much load the item puts on the sim server.
  • Download weight is an estimate how much bandwidth it takes to transfer the item from the assets server to our computers, that is, how much data needs to be transferred.
  • Render weight (or render cost or draw weight or God-only-knows-how-many-different-names-LL-has-given-that-fourth-weight-over-the-years) is an estimate of how much lag the item generates, that is how much work it is for our computers to render the item on our computer screens.

Now, Linden Lab couldn't care less about our computers or how much lag we get so that last weight is just ignored. It's the first three weights that determines the land impact. More specifically:

  • Land Impact is the highest of the three values server weight, physics weight and download weight rounded off to the nearest whole number

There are two factors there that can sometimes give unexpected results for people not familiar with the system, the rounding off part (as Rolig already mentioned) and the fact that it's only the highest of the three weights that count. You can play around with the numbers in all kinds of itneresting (at least if you happen to like math) or frustrating (if you don't) ways but let me give you a few examples.

Let's say your linkset has four meshes, each mesh has server weight 0.5, physics weight 0.4 and download weight 0.2.

If you add that up, you get server weight 2, physics weight 1.6 and download weight 0.8. Server weight is the highest, so that is what becomes the land impact.

Add a prim cube to the linkset, it has server weight 0.5, physics weight 0.06 and download weight 0.06

That will increase the server weight to 2.5, physics weight to 1,66 and download weight to 0.86. Server weight is still the highest and it is just barely high enough to be rounded up to 3 rather than down to 2. That is what probably happened in your case.

Another example:

Say you have three meshes with the same weights as the ones in the first example. That'll give you server weight 1.5, physics weight 1.2, download weight 0.6. Server weight is still the biggest and at 1.5 it is just big enough to be rounded up to 2.

Ad a cube prim to that and you get server weight 2, physics weight 1.26, download weight 0.66. In this example you could add a prim without increasing the land impact.

 

There is a third factor that can ad to the confusion btw.: the weights we can read in our viewers are with one decimal, the ones actually used for the calculations are with at least three. In otehr words, if your viewer says a weight is 2.5, it can be anything from 2.45 to 2.549. If it's 2.499 or less, it's rounded down to 2, if not it's rounded up to 3. That is never an issue with server weight for unscripted linksets since the server weight for each mesh, prim and sculpt int he set always is exactly 0.5 but it can sometiems be significant if ther are scripts adding to the server weight or if one of the other two weights is the highest one.

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1 hour ago, arton Rotaru said:

Come on, land impact is super easy. It's Longitude Of The Sun^2 * Velocity Of Hale Bopp * Pi / √(Pluto Orbit * NumberOfPrims).:SwingingFriends:

That formula would probably have worked just as well but no, it's not the one LL chose to use. I've been doing a couple of tests to determine actual load of various objects and other assets recently and it's amazing how poorly the calculated land impacts match reality.

1 hour ago, Love Zhaoying said:

Didn't this equation get updated after Pluto was decided as not-a-planet?

http://www.wired.co.uk/article/is-pluto-a-planet

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Just a visual as without one I am pretty sure I would be lost if I were new - LOL.  Depending on the item -- and IF it is the download that is dictating the land impact cost -- then making the item slightly smaller could take the LI down to 2 again. In this example for instance the mesh is all one piece (0.5 server cost), the physics is minimal (typical on small objects - I use a cube as a physics model) and the actual land impact is determined by the download (this example has high LODs at a far distance and decreases easily as it gets smaller).  

To get the information window to the left, you click on the MORE INFO link (underlined) in the building tab. 

 

 

landimpactinfo.JPG

Edited by Chic Aeon
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