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Prims, Prim Equivalent, Land Impact... a too-long guide

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Drongle McMahon wrote:

So, Phil, when will you be opening the first half-prim furniture shop? :matte-motes-smile:

Now there's an idea :)

Unfortunately, the LI system rounds floats to integers, and the minimum is 1 :(

I changed plenty of 4 prim seats to 2 prims LI though, so it's pretty good. And my 9 prim kitchen assemblies went down to 5 prims worth of LI, and that's even better.

Now I'm wondering how to present this change to customers - or even whether to present it at all, since I've been in the process of closing for the last 2 years.

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Qie Niangao wrote:

One thing devoutly to be wished is a way of displaying text on prims that is both reasonably prim-count-efficient and not subject to the security risks of Shared (or Parcel) Media.  Mesh seemed to hold such promise for this, and indeed one of my very first Meshes was a super-simple eight-material model, with all sides facing the same way, for use with a modified XYZZYtext script that I planned to write.  That would give up to 16 characters per Mesh, and as much as 32 characters per "prim equivalent" land impact.  This might make a big improvement in content efficiency on the grid, where so many prims are now used for just this application.  Except -- yep, it has to be scripted, so that means the land impact is doubled for components with such simple geometry.

Just for giggles I did that... because it's indeed a good example. I replicated a regular-prim event board as faithfully as possible. The original board had 9 rows of 40 characters (4 prims per row), plus a text clock and a "picture" frame of sorts.

4(prims per row) x9(rows) = 36 prims, plus clock, picture frame and background prim = 39 prims.

I used a flat 8-face mesh I got off the marketplace with a LI of 0.5. With otherwise identical build and 8 additional characters per row I got a total (scripted) LI of 30. So even with scripting it has a lower LI than the regular prim board. Not to mention it was one heck of a lot easier to program. :smileyhappy:

Breaking the linkset and re-linking it on demand would of course have still cut that almost in half. Probably tolerable to do for rarely-changing boards, but otherwise it'd be nasty to a sim.

And that's where it gets iffy. I'd say if it was a rapidly changing board, maybe even with text effects and whatnot, the penalty would be justified in my opinion. On the other hand, for largely static boards it's ludicrous. I wouldn't even attempt to write any logic to detect such differences in script use.

With that in mind I wonder if it might have been an intentional nudge to separate out scripted and unscripted parts of any build. It would certainly make sense.

Oh and I wholeheartedly second your suggestion of some text surface render function. llSetTextureText(string Text, integer Face) maybe?

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Jenni Darkwatch wrote:

Perrie Juran wrote:

Thank you for posting this.  It's almost scary to think you will need a slide rule to figure out best building practices. 

What still befuddles me is this.  My basic understanding of the purpose of introducing MESH was two fold.  Higher quality builds/objects.  And that building something out of MESH would have less impact than building it out of PRIMS.  Maybe if done correctly that could be true.  But so far most of what I have seen is the opposite.

You're right, that is indeed the purpose of mesh. Maybe it helps to emphasize a few important points. Mesh is far and beyond more efficient and less ressource hungry than either prim or sculpts - if built properly. This early in deployment, many mesh objects are not very efficient. As creators learn to use the tools to create mesh, efficiency will improve.

The misunderstanding that mesh is less efficient arises largely from the two independent accounting systems. The old accounting system tolerates atrocious building practices, with ostensibly less impact on our land ressources. In reality, if you examine just about
build out there, halfway properly constructed mesh would beat the pants off prim/sculpt based builds.

Client side render performance isn't necessarily related to mesh. As you noted yourself v3 performs worse even if no mesh is present. I don't know what the cause for this is, but I'd bet it has little to do with mesh per se. After all, every 3D game out there uses mesh. SL was about the last holdout on implementing direct mesh support.

That the current implementation of mesh is sub-optimal is pretty obvious. On the other hand, it's impossible to roll out a flawless feature. It'll have to evolve over time. The main concern with such new features is the introduction of "sticky bugs". SL has a few of those. What that means is that bugs get adopted as "features" and therefore become unfixable lest they break existing content.

I am with you on the sticky bugs!  Probably the biggest sticky bug out there is the default avatar height, all the so called 7' tall giants. 

And maybe this accounts for the perceived  lack of interest by LL in Avatar 2.0.  There may be too much potential to break too much content.  For example, Skins.  How will old skins looked stretched on a new bottle.  (Is there a metaphor mixed in there some where?)

My initial assumption regarding V3 was that coding was introduced to the viewer so MESH could be rendered, and that this coding was causing the problems that some of us are having.  The final vote is not in on that yet.  Regardless it has been a pain in the butt and I have wound up spending a lot of time where I should have been just enjoying SL dealing with the problem.

We can only hope that the Lab does not allow early problems to become sticky bugs.

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Great thread here!  It's great to see everyone sharing their practical knowledge and examples of how Land Impact works.


There is also a short article in the Second Life Knowledge Base that covers the basics of Land Impact.  If you think it could use any changes or additions, I'd love to see your feedback and suggestions in the comments section!

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I see that the lab kiddies have been active again in silently removing posts from the end of this thread. Maybe they want it all to finish with the Jeremy post. Maybe jeremy is the kiddie doing it. After all, when a Linden say something, it really mustn't be allowed to lose the focus, and adding posts after a Linden has said something causes it to lose the focus.

I was going to add to this thread, but the lab kiddies would throw it out of their cot.

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  • 4 months later...
  • 3 months later...

I read thru this with great interest but it doesn't explain an issue I have now experienced with turning things to the convex. I modded my store to convex hull, and SOME people can walk thru the doorway, (which is not cut out, it's made out of individual prims and framed properly) but others can't. We're all on the same viewer, but for some, it's like they're walking into a solid wall. I have no idea why this is, but I'm hoping someone can explain for me.

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  • 1 month later...

An excellent article - I only found it after I'd experimented a lot myself! A lot of experienced builders seem even now to be unaware of the possible savings here.

Server Weight is 0.5 per prim plus 0.25 per script. I can't find anything else that affects it.

Download Weight varies according to complexity but is capped at 1 per normal prim and 2 per sculpt. It is thus the sculpt limiting parameter.


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  • 2 months later...

Excellent article Jenni.

I'd been experimenting with this for a while, balancing land impact and especially trying out different ways to link solid and phantom objects without increasing land impact hugely. Finding myself using rezzer boxes a lot more to optimise land impact.

Your article put what I'd been guessing at clearly and provided me with explanations too.

I appreciate the work you put ino this very much - thank you Jenni :)

Emma :)

(And I was surprised at what I achieved in my tiny store going round optimising prims!! Wow - well worth my while!)

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  • 1 month later...

Thanks for this public service, Jenni.

It seems to me, however, that what *politically* is really happening here -- once you get through all the technicalities -- is that readings of "how much prim space remains" on a leased server, i.e. "what the land impact is" -- can very likely change for the *higher* or the *lower* -- but quite often *the higher*.

Phil thinks that if an object goes from 2 prims to 4 LI while remaining the same object, or 16 prims or 18 LI while remaining the same object, merely "opted-in" or "linked differently," that "it doesn't matter". He likely doesn't want any one to stop buying primmy furniture for fear it will use up land.

But it is using up more land. The Lindens have basically just raised tier by making the existing offer of server space in fact less. They obviously want to work very hard at hiding that news And so does the creator/scripter class -- they want to book it to FUD and "misinformation" if people see the new LI as basically halving the product and keeping the same price. But that *is* the news. And it's bad news -- a torus isn't 1 prim; it's a whopping *37* LI; 2 prims become 4, etc. This isn't trivial; it's not anecdotal; it's system wide; it has repercussions.

This explains while an old legacy build from 2005, which has been obviously there mainly unchanged in its main components since then -- for more than 7 years -- and which had never been over its parcel limits could suddenly show nearly twice the number of prims and thereby use up a buffer and make it impossible for boats to pass.

A chair that was 22 prims was now showing as 28; overall, a viewer that highlighted and showed the number of objects as 400 plus and 1800 something LI on the viewer, in fact inworld was showing 2200 on the actual land viewer, using the latest v3.

If you suddenly have to get rid of half your prims or 1000 prims, you end up having to cut the build in half, and figuring out how to fake-link prims to get them to force the "favourable reading" and all the rest described here. What a racket! What a pain! How awful!

This is exactly what I'm going through now.


Most people on a smaller parcel in a rental somewhere aren't going to notice much. Perhaps they'll not be able to put out as much stuff. Or maybe some stuff will actually book as lower now, so they cancel each other out. I've already had some tenants on the mainland get exasperated at "new readings" of their formerly prim-compliant lots. I come, and I'm perplexed, too. You count the prims in the objects by looking at edit -- but the land impact is higher, sometimes by hundreds, forcing prim overrage in a group that wrecks havocs on group rentals on mainland.

The Lindens and their chief apologists keep telling people the Party line: that the new reading system only affects mesh; that old legacy prims are essentially grandfathered; but wait, scripts might cause some different readings...and then they begin to mumble (which is why Jeremy Linden's article is so unclear -- it's deliberate -- ANYTHING but tell the customer that the product is now diminished but sold at the same price).

Everyone knows what happened to cereal boxes in the recession. The price of cereal went way up, especially after some droughts. So instead of putting higher and higher prices on the boxes of cereal so that they would become ridiculous, like US $8.00 or $10.00, to keep them at $5.82 or $6.89 or something that looked plausible, they just reduced the size of the box, and also put less cereal in it but fluffed it up with air.

When you get home and put your "new-sized" cereal box to a "legacy cereal box" in the cupboard, you see how you've been robbed -- when you open up the box and find half of it is air and there's about two bowls of cereal inside, you realize just how badly.

The same thing has happened to Second Life.


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I haven't seen or experienced a thing you describe.

Legacy builds that cost a certain amount of prims in 2005, still cost exactly the same. That is in the edit menu and in the actual LI they have (land options, available prims). Only if you click the "more info" you will see a different number, depending on the build it will be higher or lower. This number is a potential number and will only count if you set one or more of the prims in the linkset to anything but "prim" or when you link it to a mesh object. If you use a V1 based viewer the numbers don't add up, since it will only show the amount of objects in the linkset, but didn't LL stop supporting those? I have never seen any bugs in the V3 viewer regarding this. If there are, they are just bugs, showing you the wrong numbers. The only important number is actual use, visible in available prims.

I never made any working vehicles, but I think that's the only place where the new system has a negative impact. An old vehicle with a physics weight over 32 (?), no matter how much the LI is, won't work. There are some more physics glitches on older builds, but I have never seen an object gaining LI all by itself, just because LL changed the calculations.


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Prokofy Neva wrote:


This explains while an old legacy build from 2005, which has been obviously there mainly unchanged in its main components since then -- for more than 7 years -- and which had never been over its parcel limits could suddenly show nearly twice the number of prims and thereby use up a buffer and make it impossible for boats to pass.


This should not happen if the build has remained unedited during this time. However if the buildings physics type have been changed or the build has been linked to a mesh object then this could cause the issue you mentioned.

I have prefabs in my inv dating back to 2004 and none of them have acted in the way you described. In fact with some changes to the physics type and some adaption to the linksets I can generally reduce the LI of an old legacy build by 25 to 50% if I choose to.

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Did someone change the physics shape of your build, that would cause the land impact size to change, if it was changed from prim to convex hull then you'll be on the new accounting system, which can reduce the size in some cases (two linked prim cubes would have a land impact score of 1 rather than 2) or greatly increase the score if you're using curved objects or a torus.

If that didn't happen then it's a very nasty bug that needs addressing.

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There is no mesh in this build. There is no linked mesh in this build. It's an old build of 7 years, and the objects inside the building are all prims based, with a few sculpties, and no mesh objects. There are no mesh objects even on this sim to my knowledge, although there could be in the stores in a separate land group.

Viewer1 is still supported, but being phased out. But I'm on v3 so that is not the issue.

Nothing was changed in the physics. The builds were all unlinked in fact. I started to link up some of them merely to copy and save them for fear that the build would all return due to this issue.

Yeah, I get it that this "shouldn't" happen. That the reading "should" book prims in the same way if mesh/physics/scripts blah blah are not involved.

But it did. And when that happens, instead of rushing to justify LL or justify furniture and prefab makes who don't want any customer to get the idea that suddenly all their objects "weigh more" or "take up more land," you have to keep an open and curious mind, which is what I do. I don't "need" the readings to be different. But...they are.

There is the mystery of the 145 prims that returned but yet don't realy seem to be there. There is the mystery of the Phoenix viewer photo that Jadeclaw made that captured every prim, and showed right on the viewer in the highlight what the land impact should be -- 1800 something -- and then the reality of what it shows actually on the land menu inworld: 2200 something.

Each and every prim in the build will have to be examined. In each every object inside the buildings will have to be taken back to inventory and also looked at to see how it is impacting. Given that the build itself doesn't have so many prims, and the objects with the high prim counts were already removed, it seems a mystery at this point. But those who need fervently for the new Land Impact never, ever to read wrong because then it would mean there were bugs in their software or impacts on their business are not the people to get the story from on this. In needs an independent and objective investigation. I don't have the time to undo the entire build now, as I'm busy and traveling, but in about 3-4 weeks, I will get to it and take it all apart. At this point, my working hypothesis is that there is a bug in the software as played on that channel and that it is giving the overrages suddenly in the reading and that when I remove everything, and the land will appear empty, and it will not have a build in the sky, then it will show 200 or 400 or whatever non existence prims, just as the other parcel did. Now, this might "go away" if some other channel was put on it (which is why I asked for but didn't get that); it might resolve for other reasons. Meanwhile, I see the exact same thing happening on another sim now. Fortunately that sim has a big buffer.

No one is required to believe me about this but the minute it impacts one of you directly, then you'll get it. I suspect if it *is* a bug, that you will see many, many more people experience it and we will start to hear more cries. But given that the oldbies and their legacy builds don't log on, something like the return of the Ivory Tower of Prims could occur and the tree could fall in the forest without anyone hearing it...

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No one changed it.


But if a torus now reads as 37 and not 1, although the set of circumstances that make that happen do not appear to have occured, that might be an explanation.

There is one object that enables insertion of other objects into it. SO that might have been griefed.

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Dragging a box around all your prims and looking at the numbers in any viewer will likely result in a lower number than your actual use. Dragging a box ignores very small objects, dragging a box ignores everything outside the box, that is objects in the sky etc.

Look at the dates of birth of the forum users, plenty are "legacy residents", including me. I'm not saying what you describe is impossible, it is just very very unlikely. You state it as the absolute truth. I can imagine a Linden not responding well to an attitude like that.

I haven't done a complete survey of course, but I did have a quick look at the sim and on the 900 something (or was it 1400?..the one with the bazaar) parcel there are around 2000 prims according to the land menu, all of them accounted for. The other parcels are so small I can't see what's what in a reasonable time. All in all the last I would call this build is low prim.

Anyway...did you look for odd duplicates on your sim, a couple of server hiccups ago I found myself with no prims left on my land. Some objects were duplicated and I wasn't online and am sure I didn't touch any. I got the odd message about returned prims as well and found nothing in my inventory. By the names of the objects I could identify them and they weren't returned to me, they were still on the sim. Possibly they were duplicated, sent back then ignored. Luckily all duplicates (or at least I think I got them all) were near ground level so they were easy to find. There are tools out there to find prims at any height, you might want to scan your region.

The occurrance of a bug? That would be nothing new in SL. Legacy builds taking more room than they should? I still am not convinced, not even close.

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I build allot and I have to say since the rollout of mesh I have encountered allot more wierd and unexplainable problems in the course of my activities, especially in sudden changes in the LI that should not have happened. Some of these problems I have found explanations for by ripping builds apart and troubleshooting them or by scouring SL forums for similar instances and found that I inadvertently caused the problem, but in some instances I have no explanation and have to put it down to (and report it as) a bug. 

Certainly the process of rezzing and hosting content on ones land is a much riskier business than before the days of mesh, This must be particularly hazardous for land owners who rent houses, old legacy prim/sculpt houses that are editable by their tenants. There is now allot more scope for the tenant to "edit" their house and screw up the LI badly in the process.

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Oh, I totally get it about the box-dragging. Especially because this was done by someone else, not me, with Phoenix viewer, which I refuse to use, so they couldn't do "select only my objects" and they may indeed have missed some. But it was off by like 400, so that seemed odd.

What I object to is others speaking as if they have "the absolute truth" about mesh and its readings. I don't claim the truth. I don't speak as if it were an absolute truth. I say that in fact there are questions to have, you have to keep an open mind, and the last place to get an accurate and unbiased answer will be Lindens, who have a stake in this not being true, and certain builders/merchants, who also have a stake in this.

I don't see in fact that all the 2000 prims on the 4096 *are* accounted for. Since the *other* now empty parcel turned up 145 prims that just didn't exist inworld but seemed to return, I think it's possible on the other one. These two lots never showed overrages. They never overaged into a third parcel that was supposed to be kept empty for the river and boats to pass. This build has hardly changed, especially in recent months. So for this to be happening *now* means some even occurred, or the software changed.

I will go on looking at each object and the build and figure it out eventually. Odd duplicates are always an issue, I've seen that before. That happens when you rez a lot on a build tho, and this hasn't had hardly any changes. The only thing I found underneath the ground before on the other lot was an invisible copy of something that had once been rezed and deleted. That was odd. It didn't rez invisible, so it made a second invisible copy.

You can't look at lists of names of objects on the mainland. That's the frustration.


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