Jump to content

Why the drastic difference in land impact numbers in mesh objects?


Elinah Iredell
 Share

You are about to reply to a thread that has been inactive for 3364 days.

Please take a moment to consider if this thread is worth bumping.

Recommended Posts

Hi. I have been tryng to decorate my land and I need to be very conscious of the land impact numbers. I have noticed that those selling mesh home and garden creations have land impact numbers that vary drastically for items that look  a lot alike. Can someone explain why a mesh  garden pergola for instance  can very in land impact depending on the creator from 1 - 50 ?

Why are some mesh creators able to turn out items with very low land impact and others are not?  I feel frustrated because there are many pretty things out there I want to buy but the land impacts are just too high for me. Are some mesh creators just better at it than others ? Do some just not care about low land impact? I wish I understood why.

Link to comment
Share on other sites


Elinah Iredell wrote:

Hi. I have been tryng to decorate my land and I need to be very conscious of the land impact numbers. I have noticed that those selling mesh home and garden creations have land impact numbers that vary drastically for items that look  a lot alike. Can someone explain why a mesh  garden pergola for instance  can very in land impact depending on the creator from 1 - 50 ?

Why are some mesh creators able to turn out items with very low land impact and others are not?  I feel frustrated because there are many pretty things out there I want to buy but the land impacts are just too high for me. Are some mesh creators just better at it than others ? Do some just not care about low land impact? I wish I understood why.

All of the above.

Link to comment
Share on other sites

A mesh "object" is actually 4 (or so) models in one - a "full detail" version and then three (?) additional versions with lower levels of detail meant to be seen at greater distances. The land impact score takes into account all four of these versions.

Ideally, the mesh maker will carefully take into account how much detail can be dropped at each distance and hand-adjust the models so the object will look as good as possible at all distances while keeping the detail level reasonable. However, some mesh makers just re-use the full-detail model for all distances (increasing land impact) while others dramatically drop the amount of detail for all levels other than the "full-detail" one (which will give a comparatively low land impact but will run the risk of the object being ugly or unviewable from a distance.)

Many people don't notice how bad some "low-prim" meshes look from a distance because they increase the Level of Detail (LOD) factor in the viewer to a higher-than-standard level. However this means that more memory will be used to display everything and can cause performance issues.

Link to comment
Share on other sites

Thank you that is very interesting. I didnt know mesh has 4 levels and it never really occured to me to step back and observe the mesh item from a distance.  Does each level require a separate texture ? Do the resolutions on the textures make a difference on the land impact ? And does texture resolution affect lag as well?

Link to comment
Share on other sites


Elinah Iredell wrote:

Thank you that is very interesting. I didnt know mesh has 4 levels and it never really occured to me to step back and observe the mesh item from a distance.  Does each level require a separate texture ? Do the resolutions on the textures make a difference on the land impact ? And does texture resolution affect lag as well?

Textures work in a similar way but not exactly the same:

All textures are square/rectangular files with resolutions divisible by powers of two and the viewer automatically changes the resolution by doubling/having pixels as you get closer/farther from it. For example, a texture that's 256 x 256 when you place it on an object automatically gets displayed as 128 x 128 when the object's a certain distance away, then 64 x 64, and so on. (It'll never become HIGHER than 256 x 256 though.) Basically it mashes pixels together - that's why sometimes textures look blurry at first because it can take a while for them to be loaded at their full resolution.

Texture sizes aren't reflected in land impact but it can affect lag because if a texture is inappropriately large (say, a 1024 x 1024 texture on a doorknob) it will still scale down at a distance but it will always take up more memory than it probably should at any given distance.

Link to comment
Share on other sites

Without seeing the 2 objects in question it's hard to tell. But there are a couple of factors why a mesh is low, or rather high in land impact.

First of all I can't imagine that any creator doesn't care about land impact for environmental objects. (They might do not care for attachments)

As Theresa pointed out, each object in SL, be it prims, scuplted prims, or mesh have 4 level of detail models. With mesh these can be made entirely by the creator, as opposed to prims, which have the LODs set automatically. So a common practice is to reduce the mesh complexity of the 3 lower LOD models drastically, to get as little land impact numbers as possible. Some creators just don't care about how their creations look on the lower LODs, they just want to have them report an ultimate low land impact number. Which makes them look good on the marketplace listings.

In return you'll have to increase your viewer settings, namely the RenderVolumeLODFactor, to make these objects viewable without showing there uglyness at lower LODs while caming around.

This way they are also able to make the High LOD mesh even more complex than it could be with reasonable LOD meshes, and still having lower land impact numbers.

The problem here is, you are able to place alot of highpoly mesh objects on your land which wouldn't be possible with mesh models designed as the system intended them to be designed. The intention of the land impact system is to make sure that you can't place to many complex objects on your land, or you'll get bad performance.

Now with "cheating" on the LOD models, and setting the viewers LOD factor to higher numbers than the default, you circumvent the balancing system, but it has it's price as well. Even if you have the hardware to render all these objects at a higher LODFactor setting, your friend on his avarage Laptop who struggles at medium graphics settings already, might see your fancy place way different than you do. Because he is seeing alot of spikey triangles instead of the model it intended to be.

Also, every new resident in Second Life will probably start with the official viewer, on default settings. If every creator just makes garbage LOD models, with just a pretty High LOD model, these newcomers will see just alot of triangle crap.

Talking about textures: Textures aren't reflected in the land impact calculation. Though they have a huge impact on performance for sure. Depending on how many unique textures there are, the resolution of those, the alpha modes they have.

Here comes the super low land impact mesh into play again as well. The more objects you can cram on your space, the more unique textures you will likely have there as well. So performance is at an even higher risk, than just from the geometry alone.

However, again, without seeing the objects in question, it's hard to tell. But it's most likely as with everything in life. If it's too good to be true, there will be a downside to it, one way or the other. So I wouldn't say that a mesh that is only very low in land impact, compared to another which is higher, is the better mesh. In many cases it's just not. It's just designed to be very low at the cost of being ugly at lower LODs, and the requirement of higher viewer settings which can impact performance even more.

Anyhow, if you can see the objects in question in-world, you are free to choose the low land impact model, over the higher one. Though I get the feeling you rather want the model with the higher land impact, because it is more pretty, but you would like to have it at the land impact of the other. Though, it's most likely prettier because it has a more complex mesh, which comes at a higher cost. That's life. :matte-motes-tongue:

As always, there are exceptions in either direction of course.

 

Link to comment
Share on other sites

I didnt know the texture gets weaker as you move further back but I guess in sl it really has to or you would be inundated with textures coming at you from everywhere all the time.. What types of textures work best for mesh .png. .tga or . jpg?   I know textures work differently in sl then on an internet websit where jpg seems to be prefered. . I am still wondering what will happen if and when  linden rolls out their knew second life creation type world this year. I do not know if I will switch but I wonder if there will be  mesh improvements .

 

.

Link to comment
Share on other sites

It sounds like I should check a mesh item in different viewer settings before buying it to see how it looks each way. Are you saying it is better for lag and performance on your land to have a few  view highly detailed mesh items with higher land impact than a lot of lower detailed mesh items with lower land impact?

Link to comment
Share on other sites

TEXTURE SIZES.png

I don't know who made this chart or I would certainly credit them.

I'm posting it for the benefit of anyone who may read this thread.

It's amazing how fast oversized textures can chew up your memory.

This chart gives a very clear idea why using the smallest texture appropriate is so important.

 

Link to comment
Share on other sites

No, you should have low detail mesh with higher land impacts, than the ones with high detail but low land impacts.

To view the high detail, low land impact meshes, you will have to increase the RenderVolumeLODFactor, to prevent them from popping to lower LODs at too short distances already. Which forces the viewer to render even more objects at it's highest LOD, even at a distance. Also, you force the viewer to download more meshes at it's highest LOD, when entering new spaces. Instead of loading the smaller file sizes of the lower LODs first.

Rendering lowpoly meshes with even lower detail, but still reconizable as what they are in LOD models, with a default LOD factor setting, is at least the way I prefer to design my meshes. And if these low detail meshes have a little higher land impact numbers, but prettier LOD models, it's even better, because you can't put too many of them into little spaces. :matte-motes-tongue:

I know that's not the most popular opinion, but it's what I do. :matte-motes-smile:

Indeed, if you keep the LOD factor at the default, and take into account that certain meshes will pop into triangle junk, you'll have still good performance, because you render just a few triangles on them anyway. But imagine any other video game would handle it this way. I don't think anybody would want to walk through GTA V with a ton of objects popping in and out, showing just a bunch of weird triangles.

But again, there are still exceptions in either way. And without seeing the mesh....

I recently began to show  pictures of the LOD models on my marketplace listings. To give people the oportunity to see what it will look like at any distance, if it's not viewable in-world.

Like this:PillarBox_LoD_03.jpg

This Post Box has a land impact of 2. Could I make it counting just 1? Well easy! Just skipping the lower LODs and done. But it wouldn't lodding down as nicely as it does now. And I think 2 is still a low enough number for such an object, with 2 materials, and a 512 and a 256 texture applied.

As for the texture format. It doesn't matter. Any image will be converted to JPEG2000 format on upload. Just make sure you don't upload images with an alpha channel when you don't need an alpha channel. Happens alot by accident with PNGs.

Link to comment
Share on other sites


Elinah Iredell wrote:

Under which circumstances should you use a 1024 ? When should you use a 512? And for what  can you get away with a 256?

I don't know if anyone has ever made a chart, use this size texture on this size prim.

The rule of thumb is this:

"As with anything it is a balance you're aiming to achieve, as you need to use small texture sizes on small surfaces, but you don't want to go overboard and end up with a pixelated result. For example if you use a 256 x 256 sized texture on object of a certain size the result can end up looking pixelated. In this case you would need to up the texture size to 512 x 512."

http://wiki.secondlife.com/wiki/Texture_Usage

There are other people here much better versed on this topic than I am so hopefully they may have more input.

 

Link to comment
Share on other sites

The general prinicpal of having level of detail models, is to reduce the amount of polygons the hardware has to render in a scene. When objects are far away from the camera, they usually take just a few pixels on screen. Since you can't see much detail on just a few screen pixels anyway, these models can be reduced in geometry significantly, to safe in memory and geometry to render. Keeping the framerate up, while the objects are still visible in the scene though.

The distances at which objects switch between these LOD models is calculated from the distance camera to object in conjunction with the RenderVolumeLODFactor and the size of the objects. Smaller objects will switch earlier to lower LODs than larger objects. With the RenderVolumeLODfactor setting you can push the switch distances farther out, by increasing the value. Hence, rendering more objects at higher levels.

The official Second Life viewer has this factor set between 0.0 and 2.0 with the Mesh detail > Objects slider. The default for most graphis presets is 1.125.

Third party viewers may have different values set by default though, and my guess is, you are running Firestorm for example, which has set this value higher by default.

The still common advice to set the value higher, is from the time when sculpted prims got popular and people made all kind of objects out of them, which sculpted prims weren't intended for. Like having a whole table/chair set out of a single sculpted prim. They got abused badly that way, and to prevent them from popping into junk shapes on their lower LODs as well, people had to set the RenderVolumeLODFactor to higher numbers like 4.0.

Now with mesh a lot of people just cruising along that road, and don't bother to make all the LOD meshes and just give the advice to increase the LOD factor to make the items usable.

 

As for the alpha channel. Yes, alpha channels are mainly used for transparancy with Diffuse maps. But since we have Materials, you can also use the alpha channel as an emissive mask (Diffuse map), Gloss mask (Normal map), or Environment reflection mask (Specular map) as well.

Texture sizes is hard to tell. As with most things, it depends alot on the purpose of the object. One common problem in SL is, that pretty much everything you want to sell on the marketplace, is more or less a so called "Hero Object". Which means it's a main character object which will be close to the camera in video games. These have usually higher texture resolutions, than environment objects which are barely seen close up. But since we cam up close on every banana peel in SL, alot of things are textured with too high res textures, or you'll get bad reviews on the marketplace, because of "low texture quality". :matte-motes-impatient:

I recently have build me a new promenade on our sim, where I restrictively established a texel density of 64 pixel per foot, on each object. That is a  512px x 512px on 2.43 x 2.43 meters. That worked pretty well for such environmental pieces. On the larger pieces I had to create tileable textures indeed, to maintain that density with a single material.

Though, the main purpose of establishing a more or less fixed texel density, is to make sure everything has pretty much the same texture resolution, to maintain a consistent look.

However, working with a desired texel density in mind makes it easier as well, to determine which resolution would be best suited.

Another aspect is combining multiple small textures into one texture sheet. If you have an object with 4 materials, and four 512 textures, you would be better of combining them into one 1024, and having them all on the same material if possible. To reduce draw calls.

Ok, I guess that was a bit much for just one day. :matte-motes-bashful-cute-2:

Link to comment
Share on other sites

The LOD steps also apply to old fashined prims. Here is a picture of the geometries standard prims as they are rendered at different LODs in SL.

llprimlods.jpg

Here are the numbers of triangles the gpu has to render for these.

llprimlodtris.png

With Mesh. the creator has complete control over the geometry at each LOD. If used carefully, that makes for gentle reduction in detail as you get further away. If it's used badly, it can produce very sudgen and ugly effects from too much reduction, or very high LI from too little reduction.

Link to comment
Share on other sites


arton Rotaru wrote:

 

Texture sizes is hard to tell. As with most things, it depends alot on the purpose of the object. One common problem in SL is, that pretty much everything you want to sell on the marketplace, is more or less a so called "Hero Object". Which means it's a main character object which will be close to the camera in video games. These have usually higher texture resolutions, than environment objects which are barely seen close up. But since we cam up close on every banana peel in SL, alot of things are textured with too high res textures, or you'll get bad reviews on the marketplace, because of "low texture quality". :matte-motes-impatient:


Interesting perspective on the "hero object."

But as you point out, in a sense it's a judgement call, how crisp and detailed ypu want something to look when someone zooms in on it.  Some things can look fine from a distance but like mush up close.  And no, I don't like things that look like mush.

But still, really you can only zoom in (enlarge) so far.  So it would be doubtful you'd need a 512 on a micro prim link on a necklace.  Or on a door knob.

I'd guess with experience you'd get a feel for what you are going to need.  I know the $L's can start to add up when you upload textures,  but given the rarity that large textures are need, people should start smaller and on the rare occasion you find you need that massive 1024 it won't break your bank.

Link to comment
Share on other sites


Perrie Juran wrote:


arton Rotaru wrote:

 

Texture sizes is hard to tell. As with most things, it depends alot on the purpose of the object. One common problem in SL is, that pretty much everything you want to sell on the marketplace, is more or less a so called "Hero Object". Which means it's a main character object which will be close to the camera in video games. These have usually higher texture resolutions, than environment objects which are barely seen close up. But since we cam up close on every banana peel in SL, alot of things are textured with too high res textures, or you'll get bad reviews on the marketplace, because of "low texture quality". :matte-motes-impatient:


Interesting perspective on the "hero object."

But as you point out, in a sense it's a judgement call, how crisp and detailed ypu want something to look when someone zooms in on it.  Some things can look fine from a distance but like mush up close.  And no, I don't like things that look like mush.

But still, really you can only zoom in (enlarge) so far.  So it would be doubtful you'd need a 512 on a micro prim link on a necklace.  Or on a door knob.

I'd guess with experience you'd get a feel for what you are going to need.  I know the $L's can start to add up when you upload textures,  but given the rarity that large textures are need, people should start smaller and on the rare occasion you find you need that massive 1024 it won't break your bank.

Hehe, just in case...

with Draw Calls I wasn't referring to draw  L$ by combining multiple textures into one larger texture sheet. It's when the render state changes to load another material/texture into the GPU, which is done by the CPU. The fewer commands the CPU has to talk to the GPU, the more efficient the GPU can do it's work.

As I mentioned, establishing a texel density on a pixel per foot/meter basis tells you quickly what would be a good texture size for the item. Of course, you shouldn't set that density at 500 pixels per foot. :matte-motes-smitten:

Link to comment
Share on other sites

Its true then that smaller things do not need high resolution images it makes sense I never though of that . What about skins? Some use 1024 textures while some use 512? And the same for mesh textures on clothes  ? Is that why some people look invisible when wearing mesh and others do not?

Link to comment
Share on other sites

You are about to reply to a thread that has been inactive for 3364 days.

Please take a moment to consider if this thread is worth bumping.

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
 Share

×
×
  • Create New...