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# What is the maximum number of poly to stay under 1 prim?

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hello , is there a specific maximum number of poligons to be able to stay under one prim when expoerting a mesh ?So to know how to model something and be sure to have 0.5 prim impact

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LI depends on three things.

Download, Physics and SIZE so "just" knmowing the poly count doesn't really give you an answer. SMALL will almost always give you a low land impact number even if the poly count is fairly high.

After awhile you get a "feel" for what the LI "should" be with reasonable LOD and good physics. But as far as I know there is no MAGIC poly number *wink*.

Best to make your items as simple as they can be and go from there. Good luck.

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Chic Aeon wrote:

After awhile you get a "feel" for what the LI "should" be with reasonable LOD and good physics. But as far as I know there is no MAGIC poly number *wink*.

Most important thing is the LOD models you use. If the object is large, make sure the highest LOD doesn't have a high number of polygons. If the object is small, make sure the lower LOD is fairly simple in geometry.

Drongle made an analysis on this a few years back. I'm not sure if anything has changed since then, since that was written in the early days of mesh, but the principle still stands either way. It IS a bit technical.

My advice would also be to build something very basic, upload it and then see what LOD model needs adjustments. The graphs Drongle made could behelpful to see where you can win the most.

I understand this answer isn't very fulfilling, but consider the answer to the question: the highest possible number of polygons in your mesh is as many as will fit in a mesh, which is 100's of 1000's. (There's a specific number for that, can't find it right away), as long as you make the object very small, the physics simple and keep all LOD models lower than the highest at a single triangle. Well, I'm pretty sure that will still generate a LI of 0.5.

If you want to do some investigation on your own, you can have a look at how others did it. Find a model inworld, open the development menu, show info, show render info. This will give you a white console at the right of your screen. Select the object. On one of the lower lines it will showyou the amount of KTris (1000 triangles). Now zoom out and cycle through the 4 LODs.

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As Chic said, size can be quite significant here and there is no absolute answer to how many polys you can have.

But perhaps a short explanation how LI is calculated will help.

The way you ask, I'm sure you know this but just in case: LI is based on three of the four "weights" that are estimates how much lag the object causes.

• Server weight is how much work it is for the servers to retrieve the object info from the assets database
• Physics weight is how much work it is for the sim server to calculate the physics shape of the object
• Download weight is how much data needs to be transferred

The land impact is the highest of these three weights, rounded off to the nearest whole number. In a linkset, each weight is summed up separately before the LI for the linkset as a whole is determined

(There is a fourth weight too, render weight  (aka display weight or display cost) but that's about how much work it is for our computers to handle the object and Linden Lab couldn't care less about that so it's not taken into account for the LI even though that is where the lag actually happens nowadays.)

Server weight is easy to calculate. It is always 0.5 for each part of a linkset plus somehwere between 0.2 and 0.3 for each active script.

Physics weight depends on the physics model and it can be a bit of a black art to get that as low as possible. Usually that's not the limiting factor though.

Download weight is the sum of the file sizes for each LOD model weighed towards how often it is estimated that LOD model will be needed. The reason a larger mesh usually has higher download weight is that it needs the higher, more detailed, LOD models more often sicne they're used for longer view distances. The file sizes for the lower LOD models count for more than the higher ones, since they will always be downloaded more frequently.
Size and poly count are not the only factors here though because the files transferred are not raw data, they are compressed. How "compressable" the files are, can have a huge impact on the download weight. It is not unusual for barely noticeable tweaks to a model to more than double or halve the download weight. Even the exact syntax of the dae file matters here. Drongle once made some test where he could alter the LI simply by changing the order the polys were listed in the dae file. And since all mesh creation programs use different dae syntaxes, which application you use will affect the downlaod weight. Optimizing a model for compressability is again a bit of black art but there are some obvious techniques such as aligning vertices and polys along the axises whenever possible (on the UV map too btw - that's jsut as important).

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As an example I did an object that has :

Download :1.1

Physics 0.2    ( its just a triangle, not sure how can I go further down here )

Server 0.5 ( also is this the minimum and what is affecting that ?

If I remove all lods and just type 2 poligons in the generator it creates a mesh with 0.5 prim

Is the 0.5 prim the minimum possible?

I also noticed that its ifluenced by the fact that I have two or one ID material , one for lods and one for main ,if I reduce that to just one then I shoudl get a better count , but problem is I have to renounce to a HD texture , Is there a way to load a highrerres one?

Could I go further down under 1.1?

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Also another question is :

is better to export lod and Hd version as one single mesh with different IDs or as two separate objects , that so in viewer can even be delinked?

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"Drongle made an analysis on this a few years back."

A more complete analysis followed in this thread. Still very technical. As far as I know, nothing has changed.

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Ah yes, that's the one I had in mind I looked at your pictures and apparantly found the older one.

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Assuming HD is the high detail visible mesh, and lod are the lower detail meshes, they have to be in different files. So they can't be in one mesh. They are never rendered at the same time. They are alternatives. Which is rendered depends on how far away the object is from the camera, its size, and the setting of the RenderVolumeLODFactor setting (eg via Object Detail ... or via graphics quality). If this is a new project, you probably need to read this KB article so that you can use the new naming convention for objects in LOD files*, especially if you have multiple mesh objects. Multiple objects become a linkset inworld, which can be unlinked just like linksets made there. The naming convention is to ensure that each high-detail object gets associated  with the correct object in the lower LODs. Note also that you need one object in the lower LOD file for each in the high LOD file, and that the lower LOD objects will be squashed or stretched to fit the bounding box of the corresponding high detail object. Both of those apply to the physics model objects too, in the physics file.

*See my comment there - Although the main text suggest it, it is not the filenames that have to use the convention, it's the names of the objects inside them.

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Naiman Broome wrote:

Is the 0.5 prim the minimum possible?

Yes. As mentioned, the LI is the highest of the download, server and physics weight. The server weight has a minimum of 0.5. If the download and physics weight are a lot lower than 0.5 you could consider combining several objects.

I also noticed that its ifluenced by the fact that I have two or one ID material , one for lods and one for main ,if I reduce that to just one then I shoudl get a better count , but problem is I have to renounce to a HD texture , Is there a way to load a highrerres one?

The largest texture you can upload is 1024x1024. No way around that. You could set up your lower LODs in such a way they use the texture for the highest LOD. That's not always possible of course. Also take in mind the lower LODs don't need a very large texture, so let's say 10% (just throwing out a number) of your 1024x1024 should probably be plenty.

Could I go further down under 1.1?

Only one way to find out

I suspect that if you reduce the texture IDs to one you would.

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Naiman Broome wrote:

Also another question is :

is better to export lod and Hd version as one single mesh with different IDs or as two separate objects , that so in viewer can even be delinked?

You should upload as a single model. Simple reason, you can't set your highest LOD lower than your lower LODs. I don't see any benefits to allow them to be unlinked anyway.

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Thanks. I  don't have any issues as I learned from some good folks (thank you all).  Most everything I make in the decor and furniture line (even fairly large things) are 1 or 2LI. Houses 35ish (47 for a BIG one with lots of french doors that I just uploaded). I really HAVE paid attention. I am far from perfect, but I definitely know what NOT to do (and rarely do that these days LOL).

I guess what I maybe should have said as more of an explanation is that after awhile when you see a -- let's say "chair" -- it is easy to decide what the LI "should" be if  the person uploading did some testing and LOD models as needed.  So when I see a "chair" that is 15, I know that something wasn't optimal. It could have been a heavy finger on the subsurf modifier; it could have been LODs to see the chair from across the sim (not really all that necessary in my book).

So IF your item uploads too heavy, then something needs to be fixed. You can tell that even before you upload and test the LODs in world.  I use 2 LOD factor for testing which is Firestorm's default, but some viewers are 1 or 1.25.  I have a feeling some of those folks are seeing a fairly different world than those with LODs on 4.

For ME, the most important part of the process is testing inworld. I have a few very nice things (not mine) that when viewed at 2.0 fall apart from within a small room. Now that aint good.   So especially if you are just starting out, be sure that you make that testing inworld (with whatever LOD you decide to design for -- and there have been many threads on that over the years and just as many opinions) part of the process.

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Just wanted to note that there have been many discussions on this forum about using different textures for the different LODs and the general consensus was that it wasn't the best idea. I am sure someone that did the tests and has an opinion can pipe in here OR you might be able to find one of the threads on this in the archives.

I read them all but don't remember specifics, just that "for me" the single texture was going to be the choice .

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I only replied to your post because you mentioned the LOD models. Everything I said was really addressed to the OP.

Sorry for the confusion:)

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Chic Aeon wrote:

Just wanted to note that there have been many discussions on this forum about using different textures for the different LODs and the general consensus was that it wasn't the best idea.

It is generally not a good idea. But there are exceptions when it makes sense to use an impostor texture for the lower res models. An imposter texture is a separate face with an picture of the item - or a particularly detailed part of it. It is hidden in the high resolution LOD model and brought forth in all or some of the lwoer ones.

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Drongle McMahon wrote:

Assuming HD is the high detail visible mesh, and lod are the lower detail meshes, they have to be in different files. So they can't be in one mesh.

To avoid a possible misunderstanding here, the different LOD models are created as separate mesh files but they are uplaoded as a single mesh. In the uplaoder, select "from file" for each LOD model and then select the apropriate file from your harddisk. The uploader will then combine them all into a single SL mesh.

Speaking of LOD models - I know I'm repeating myself here but it's rather important: One of the cheats unskilled mesh makers use to reduce the land impact, is to butcher the LOD models. You can save a lot of LI that way but the item will look horrible even at moderate viewing distances. So be very careful which details you include in each LOD model and never ever let the uploader generate them!

The benchmark for good mesh is that it looks ok with default mid quality graphics settings (that is RenderVolLODFactor 1.25 and draw distance128 m) at any distance until it's so small you won't see it or it's cut off by the draw distance. For items specifically made for indoors use or in other restricted spaces, you can lower the requirement a bit but with the room sizes you sometimes get in SL, it should still be perfectly good looking at - say 30 m distance. Any mesh that doesn't meet these requirements is sub standard and no builder who takes pride in their work want that of course. (Except, this applis to "public" mesh - items you sell or give away or palce in public view. What you make and upload for your own private use in your own private place is niobody's busniess but yours.)

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Naiman Broome wrote:

Physics 0.2    ( its just a triangle, not sure how can I go further down here )

0.2 is the lowest possible phsyics weight for an upload but you can get it all the way down to 0 afterwards by settign the physics shape to "none" and you want to do that if possible since a mesh with a single triangle physics model won't have a physics shape that makes any sense anyway.

Naiman Broome wrote:

Could I go further down under 1.1?

Depends on the complexity of the object. The lowest possible download weight is 0.06

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ChinRey wrote:

The benchmark for good mesh is that it looks ok with default mid quality graphics settings (that is RenderVolLODFactor 1.25 and draw distance128 m) at any distance until it's so small you won't see it or it's cut off by the draw distance. For items specifically made for indoors use or in other restricted spaces, you can lower the requirement a bit but with the room sizes you sometimes get in SL, it should still be perfectly good looking at - say 30 m distance. Any mesh that doesn't meet these requirements is sub standard and no builder who takes pride in their work want that of course. (Except, this applis to "public" mesh - items you sell or give away or palce in public view. What you make and upload for your own private use in your own private place is niobody's busniess but yours.)

I just wanted to add a bit of a pragmatic comment here.  In the best of all possible world's and platforms I agree with you  -- but of course there is a "but" (a big one).

Our platform is based on a system where prims (LI) are directly tied to money -- money that needs to be spent EACH MONTH in order to support the items we rez on our land. If you are a creator that expects to sell things, you really NEED to keep items under a certain land impact count. If you don't (and you are trying to sell) you might as well stop as no one will buy your items. So there are choices to be made and each content creator makes them.

My personal choices are somewhere in the middle. I try to make the mesh simple enough to start out with (well I have a megaphone that I made long ago still floating around which is heavier than hell -- but in general and TODAY for sure ). I let the cycles textures do much of the work of presentation. For ME, that works. I use biggish textures because FOR ME and the people I sell to -- details are very important.  I want most folks (the ones that buy and use  high end decor items for example) to be able to see the items well. I want the houses to be seen part way across the sim but I am willing to make a few exceptions rather than compromise the design so folks using LOD 1 will not see things at their best far away.  I try and balance the needs of the mesh and the needs of the people.

There have been threads about "the best" way to design -- some here I think, some on the merchant forum. Different folks have different opinions AND different CUSTOMERS.  Heavy mesh hurst everyone on the server,  so that is a problem for us all. But choices in LODs ARE choices made by the individual creator.  In many cases they are designing for "their customers" who in most cases see (or have the opportunity if they take the time) the objects in world.

I don't agree with the choices of some creators but they are THEIR choices and some are made purposefully, so while your statement above is certainly your truth -- I personally do not believe it is THE truth .   Everyone has a right to make their own choices. Some don't understand the variables, I agree. But others definitely do (they have spoken their mind on other threads) and while that may make them a substandard creator in YOUR mind, I am guessing it doesn't in theirs.

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Chic Aeon wrote:

Our platform is based on a system where prims (LI) are directly tied to money -- money that needs to be spent EACH MONTH in order to support the items we rez on our land. If you are a creator that expects to sell things, you really NEED to keep items under a certain land impact count. If you don't (and you are trying to sell) you might as well stop as no one will buy your items. So there are choices to be made and each content creator makes them.

Yes but even with those quality level requirements, if the mesh is well made, you'll run out of land to build on long before you run out of prims even on a homestead sim.

The fact is, there are so many more efficient and less destructive ways than LOD butchery to reduce a mesh' land impact. It just takes a little bit of thinking, a little bit of studying, a little bit of understanding. So no, LOD butchery is not a way to save LI, it's just an excuse for lazy and/or incompetent builders not to do a proper job.

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