Linking columns

[Umaeril]

Is it the norm that linking columns leads to huge land impacts? 

Thank you! 

[arton Rotaru]

Simple question deserves a simple answer.

No!

 

Seriously, if you link a mesh to a regular prim build, the whole linkset will be subject to mesh accounting. And the land impact can be very high, denpending on the physics shapes of the prims.

There may be ways to reduce the land impact, by changing the Physics Shape Type of the prims and meshes. But it all depends on of what you have there actually. 

There are also a couple of other factors which will make a prim object opt-in to mesh accounting. "Linking columns" is rather vague information to deal with.

 

[Madelaine McMasters]

Hi Umaeril,

I don't think there is a "norm" when linking things these days. If your linkset is prim only (no mesh), then every prim should have a land impact of one, unless you set the physics shape of any prim to "none" or "convex hull". The moment that happens, all prims are evaluated according to LI rules, not the old prim rules. Curved shapes will jump in land impact when that happens. The same will happen if you link in any mesh objects. Torturing a prim makes things even worse.

So, check your linkset for anything with a non "prim" physics type, or a mesh object. Change the physics shape to "prim" and remove any mesh things.

 

[Umaeril]

These are prim cylinders made into colums, 8 of them. They are quite simple. But when I try to link to another cylinder which I wish to make my root prim, which has been path cut, the LI is over 600. So what am I doing wrong please, if anyone knows. Or if you can  IM me inworld, the name is Umaeril Resident. Thanks, I will check back here though either way. 

[arton Rotaru]

If it's prims only, make sure there is no texture set to Alpha Mode "Masking", or "Emissive" under the texture tab.

Then Select the linkset, go to the Features tab in the Build floater, and select "Prim" under the Physics Shape Type drop down menu.

[Umaeril]

Thank you all for your replies so far. There is no alpha mode or masking on or anything else that alters the physics shape. I went and made myself another set at a sand box albeit a smaller quick version and the LI is 9 just like it should be. Perhaps there is something wrong with the prims that I did make though, I think one of them may have been a sphere originally. 

I will next try to make a large set and see how that goes (it's not huge, just making a gazebo).

In theory, I should be able to link together colums and half-spheres and (non-tortured) prims and get the same LI as I have prims being linked, is that correct? Are there some shapes, non-tortured, when added to a linked set of prims makes the LI go way up? A torus perhaps? I am speaking strickly about prims. 

[arton Rotaru]

Regardless of the prim type, it will always count any prim as 1 under the legacy accounting.

What I forgot to mention, the mesh accounting is also triggered when a face has a non default setting for the material maps. If you have a normal, or specular map added to one, or more faces.

[Pamela Galli]

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Umaeril wrote:

Thank you all for your replies so far. There is no alpha mode or masking on or anything else that alters the physics shape. I went and made myself another set at a sand box albeit a smaller quick version and the LI is 9 just like it should be. Perhaps there is something wrong with the prims that I did make though, I think one of them may have been a sphere originally. 

I will next try to make a large set and see how that goes (it's not huge, just making a gazebo).

In theory, I should be able to link together colums and half-spheres and (non-tortured) prims and get the same LI as I have prims being linked, is that correct? Are there some shapes, non-tortured, when added to a linked set of prims makes the LI go way up? A torus perhaps? I am speaking strickly about prims. 

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Yes Uma (waves!) a torus is notorious for driving up LI, esp when cut. I believe that cutting spheres will do so as well. Nine plain cube columns should come out to no more than 6 LI.

 

[Umaeril]

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arton Rotaru wrote:

Regardless of the prim type, it will always count any prim as 1 under the legacy accounting.

What I forgot to mention, the mesh accounting is also triggered when a face has a non default setting for the material maps. If you have a normal, or specular map added to one, or more faces.

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Hi, thanks for your suggestions, I did not have any materials enable. That is good to know though, I did not know that it could do that, thank you. 

 

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Pamela Galli wrote:

Yes Uma (waves!) a torus is notorious for driving up LI, esp when cut. I believe that cutting spheres will do so as well. Nine plain cube columns should come out to no more than 6 LI.

 

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Hi Pam (waves back! ^^) I suspected that about toruses, oh that is too bad about the spheres though. Noit sure how you got 9 prims down to 6LI, but also mine are cylinders if that makes a difference. 

 

[arton Rotaru]

Like you can increase the LI of prim linksets with mesh accounting, there is also the possibility to bring the LI down.

Select the linkset and set the Physics Shape Type to Convex Hull, and see what happens. Select the sphere and set it to physics shape type: None. Type None only works on child prims though.

[ChinRey]

Quick(-ish) explanation first:

• Land Impact is an attempt to estimate how much load an item gives Linden Lab's servers and internet connection. Originally the calculation was very simple: one prim equals one land impact. This turned out to be to inexact in the long run though so LL introduced a new and slightly less inexact way to calculate LI.
• LL decided to keep the old prim count system as an alternative for old style builds. The reason for that was that some (although very few) old builds have so high actual land impact they would go over their sim's LI limit and be autoreturned if they were suddenly to be calculated the new way. It is important to realize that preservation of old builds is the only reason why the old system is still in use. That means that any function or feature introduced after the new LI system, will switch the entire linkset to the new LI system. Arton has already mentioned the most common causes but there are more, far more, and the list is still growing. So the question is: what feature does the linkset contain that didn't exist in Second Life five years ago? (Not just visual features btw, scripts with some recently introduced functions will also cause a LI system switch.)
• Most prims actually have a much lower land impact with the new than the old system so usually you want your build calculated the new way. This is why Pamela is talking about 6 LI for nine prims. Judging by your description, you should actually be able to get it down to five.
• Huge jumps in prim LI between the two systems are always caused by physics weight and that can be manipulated with the three different physics shape types. If you know how to use those, you will nearly always get a result at least as low with the new LI system as with the old.

 

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 Slightly longer explanation:

I wrote a notecard about the LI jump problem a while ago  (Wow, nearly two years ago actually! Time runs fast!)

If anybody wants a copy of the notecard to share with their friends and fellow builders, just contact me in-world and I'll give you a copy. It's supposed to be freely distributed.

If you just want to read it for yourself, here is the complete text - my sneaky promotional links and all. ==

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LAND IMPACT MYSTERY SOLVED

(OPQ Guide Cards to Second Life: Builder)

v. 1.1, 2014-04-21

by Rey (ChinRey Resident)

Just a very short explanation to one of the problems most builders run into every now and then: Why does the land impact (or "LI" or "prim count") suddenly raise or drop when objects are linked together?

Index:

1. The History of LI

2. The Jumping LI Problem

3. The Solutions

4. About OPQ

5. Copyright Notice

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1. The History of LI

Originally the land impact of a linkset (that is a set of objects linked together) was calculated very simply: 1 LI for each prim.

That didn't work in the long run though. LI is supposed to indicate how much load an object puts on the servers and the network and different types of prims can be very different there. The problem became even more critical with the introduction of mesh - there simply is no sensible way to handle meshes with that old system.

The only solution was to introduce a brand new model for calculating LI, based on three of the four "weights" an object has. This modern calculation is far from exact but it gives a much closer estimate of the actual load the objects causes.

There was still a problem though: Quite a few older builds would break under that new calculation method, that is their LI would increase beyond the limit allowed.

The solution to that was to use both calculation methods in parallel: anything that could have been built before the new LI formula was introduced still has its LI calculated the old way, anything that includes features that didn't exist back then, is calculated the new way. Quite confusing and hardly an ideal solution but there really was no alternative.

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2. The Jumping LI Problem

One problem this dual model causes, is that the LI of a linkset can suddenly jump up or down when objects are added or modified. It only takes a single object with a single modern feature to switch the whole linkset between the two formulas and the difference in LI can be huge. Usually the modern formula gives the best (that is lowest) result but there are exceptions and it's not that uncommon for LI to increase by several hundreds - or even thousands - if the modern LI formula is triggered.

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3. The Solutions

a) To trigger modern LI calculation

This is what you usually want to do and the solution is simple: just introduce one modern feature. Usually what you do is "convex" the linkset, that is change the Physics Shape Type to convex hull. One minor warning though, some prims may act a little bit funny when convexed. If that is a problem, just keep the physics shape type of those prims as "Prim". You only need to convex a single prim in the linkset to trigger modern LI calculation.

b) To fix LI jumps

The reason why the old method of LI calculation is kept is that some older builds have very high actual LI - in extreme cases several hundred or even thousand times the number of prims they contain. There aren't that many of them but it can be a rather nasty surprise if the one you're working on is one and you do something that triggers modern LI calculation.

The simplest and most obvious solution is of course to revert the build back to its original state. But maybe you'd want to fix the problem instead?

As far as I know, huge LI jumps are always caused by physics weight. (In theory it can also be caused by download weight but I can't think of many realistic scenarios where that will actually happen.)

So the first thing we should try do is to reduce the physics weight. No, the very first thing we should do is take a backup copy of the linkset into our inventory, *then* we take a look at the physics weight!

An object in SL can have three different physics shape types:

• Prim: more or less the same as the shape you see.

• Convex Hull: A simple rectangular or triangular box around the object. Can give a much lower physical weight than prim.

• None: No physical shape at all. More or less the same as phantom - except it works for individual objects within a linkset. Removes physical weight completely.

The physics shape type determines the object's interaction with an avatar. It's the shape you crash into or walk upon. Usually it has no other function than that.

To minimize physics weight, keep all objects that actually need a detailed physics shape (the ones with walkable surfaces, hollow prims you're supposed to walk inside or through etc.) as "Prim", change all objects you're not supposed to interact physically with to "none" and change everything else to "Convex Hull".

Smaller LI jumps can be caused by download weight or physics weight. If it's physics weight, you can use the method above but usually there's no simple way to reduce download weight so if that is the problem, the only easy solution is to revert the build. That is, unless you're desperately short on LI, you can just leave it as it is. After all, the two different calculation methods don't affect the actual lag/load the object generates - the modern LI calculation is just a more accurate estimate of it. So unless you're running out of LI, the jump doesn't really have any practical significance.

c) When the LI count doesn't revert

Sometimes when you revert a linkset to use the old formula, the LI figure you get in the Build window stays high. It might be that there is some minor detail you missed when reverting the build but most likely it's just that the data isn't updated. If so, you can unlink and relink to force another recalculation but there's no real need to worry. The LI count you read in the Build window is calculated by your viewer and not the server and it shouldn't take long for it to be updated anyway.

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4. About OPQ

• OPQ Main Store

Marketplace stores:

OPQ Builders' Supplies:

https://marketplace.secondlife.com/stores/167633

Bel's Scripts:

https://marketplace.secondlife.com/stores/165683

OPQ Gardens and Landscaping:

https://marketplace.secondlife.com/stores/167694

OPQ Interior:

https://marketplace.secondlife.com/stores/167689

Chin Rey Houses:

https://marketplace.secondlife.com/stores/154697

OPQ Estates:

https://marketplace.secondlife.com/stores/167695

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5. Copyright Notice

This notecard was written 25.03.2014 and updated 12.04.2015 by Rey (ChinRey Resident). Please feel free to distribute it any way you like as long as you don't change the text or charge any money for it.

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[Pamela Galli]

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Umaeril wrote:

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arton Rotaru wrote:

Regardless of the prim type, it will always count any prim as 1 under the legacy accounting.

What I forgot to mention, the mesh accounting is also triggered when a face has a non default setting for the material maps. If you have a normal, or specular map added to one, or more faces.

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Hi, thanks for your suggestions, I did not have any materials enable. That is good to know though, I did not know that it could do that, thank you. 

 

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Pamela Galli wrote:

Yes Uma (waves!) a torus is notorious for driving up LI, esp when cut. I believe that cutting spheres will do so as well. Nine plain cube columns should come out to no more than 6 LI.

 

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Hi Pam (waves back! ^^) I suspected that about toruses, oh that is too bad about the spheres though. Noit sure how you got 9 prims down to 6LI, but also mine are cylinders if that makes a difference. 

 

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If you can send me a mod trans copy I would like to see them, Uma.

[Umaeril]

Hello ChinRey, thank you very much for the explanation, very helpful. I will keep this in mind going forward.

 

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Pamela Galli wrote:

If you can send me a mod trans copy I would like to see them, Uma.

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Hi Pam, I would love to send you a copy but I unlinked it and all I had anyhow was a base and 8 columns. I am trying to do a gazebo like this: 

https://marketplace.secondlife.com/p/Small-Furnished-Gazebo-Mini-Skybox/3463728

 

I did buy the above gazebo when I first arrived in SL, not understanding it was 90 prims. That is why I want to build my own instead with less prims. The sample gazebo is not modify.  

I know that convex hull may prevent entry to areas, is that so with a gazebo like this?

 

 

[Pamela Galli]

If those are regular prims, it will not be 90 LI for just the Gazebo, but 12.  When you set it to convex hull then that cut and hollowed prim could give you some ridiculous LI. I will never forget my simple arched wall with 8000 LI, when set to prim.

[arton Rotaru]

You could bring it down to 7 instead of 12, with working collision shapes, when you keep the hollowed, pathcut cylinder unlinked, and as type Prim, and set the rest to Convex Hull.

That might be appropriate if you just want to keep this for your own use.