Poly Counts

[fsbrown]

Ok, I'm relatively new to Trainz can someone explain poly counts to me at a simple level? How does it effect images? How does it affect computer performance and the display? Are there rules of thumb on how much a route handle or does it depend on the computer hardware? How can you tell how many poly counts or whatever you call them each item has? How can you tell which items have higher poly counts than others?

Admittedly, I just don't understand.

 

[Dinorius_Redundicus]

Can someone explain poly counts to me at a simple level?

'Polygons' refers to the triangles that every 3D mesh is made from. 'Poly count' is just the total number of triangles. In professional circles, they call them tris, but everyone around Trainz still calls them polygons. Polygon of course just means 'many sides', whereas a tri is more specifically a 3-sided polygon.


How does it affect images?

Poly count doesn't affect images, if by images you mean the textures on the 3D mesh. It can affect the appearance/realism of the object - too few polys and the object will look blocky.


How does it affect computer performance and the display? Are there rules of thumb on how much a route handle or does it depend on the computer hardware?

For every computer there will be a maximum number of polys in a scene that it can draw and keep track of without the frame rates slowing down. I don't know what that number is, but it will vary with the quality of the video card and maybe with the speed of the hard drive read/writes etc. So, the less polys the better for fast, smooth rendering of scenes. Performance can suffer if too many separate texture images are used on a model - one texture is worth about 200 polys in terms of the computer 'resources' needed to handle it. Good modellers strive to stick all their textures into just one image, but sometimes you have to use 2 or 3 due to the technical requirements of the texture mapping. More textures than that is a sign of a slack/ignorant modeller. I think the record is 50 textures on one model - really bad.


How can you tell how many poly counts or whatever you call them each item has? How can you tell which items have higher poly counts than others?

There's no way to tell just by looking at it. However, in Content Mangler, select an asset and I think a right-click will show a menu which has an item called something like 'mesh technical properties'. This will list various parameters including poly count. Or, if you can open the asset's folder and see the mesh file itself (it will be either a .im or .pm file) you can use PEV's "Mesh Viewer" utility (a freeware program) to open the mesh, right-click and view 'mesh data' to see the poly count. I think both methods can also tell you how many different textures are used on the mesh.

 

[Wessex_Electric_Nutter]

I think the record is 50 textures on one model - really bad.

FIFTY textures? What model was that?

 

[Azervich]

FIFTY textures? What model was that?

There's lots of models with that amount, I was one of those people who created models using simple texturing and with help from others I've been able to map on single textures.

Anyways

I've become one of those people who won't use an asset if it's more than 7 single textures as there's also a limit on how many trainz can render

I think N3V should add a tag in cmp to help modellers with building models with high polys, something like

Warning: The model is over 1,000 polys and Level-Of-Detail meshes is recommended

Something like that, would help improve trainz because of the 5km draw distance the new ones have.

Once your at the 900m range you don't need any details and you can pretty much get it as low as 100-300 polys on something that might be 10,000 polys when your 1m away

Just my thoughts and opinions.
Cheers.

 

[johnwhelan]

In simple terms before TS2009 Trainz would use the cpu to draw each triangle or poly. TS2009 pushed a lot more work on to the GPU (graphics card) so in native mode the Frames per second went up and poly counts became less critical.

Each mesh has an overhead of 300 poly equivalents, each texture has an overhead of 200 poly equivalents.

TS2009 was the first to use DXT compression which effectively cuts the texture size down to 25%. It also made more effective use of GPU for normal mapping which is a way of 'faking' detail without using polys.

There are some performance sliders which control things such as how far you can see things in the distance. Setting them to the left reduces the distance and hence the number of objects to be drawn.

Stations and towns with lots of assets are more challenging for Trainz often the overhead for an asset is more than the poly count so some creators will put more than one house in an asset. An example would be KUID: 86627:100035 which probably isn't suitable for your layout.

Different computers do differ in their ability to handle high poly items but the content makes the biggest difference. For example using an object made of triangles and cubes such as a house. How often do you look at the underside? If the content creator doesn't delete the unseen faces Trainz knows no better than to draw them each time. It adds nothing to the image but does add to the overhead.

When you are close to a steam loco its nice to be able to see the individual pipes etc. when its a mile away you can't see the pipes. That's where lod (level of detail) comes in, you use a simpler model that shows all the detail you can see but with a much lower poly count.

At a simple level avoid scenery objects with poly counts in excess of a thousand. This is a very rough rule of thumb, I have a block of 48 houses that have a higher poly count than this. Sketchup is particularly bad at adding unseen faces and splitting faces up into smaller faces than necessary so typically avoid the newer Sketchup models.

Professional game designers get a poly budget per scene, within this budget they will sometimes include one or two higher poly objects as long as the total of all the objects is below their budget.

Desktops in general can handle higher poly counts, Laptops and smartphones you need to be a lot more choosey about content and how it is placed.

Finally some content does not run well in TS2009 and above, splines can be a problem. Under Options there is a developer tab, show performance whatever in surveyor. Use this to identify poorly performing assets, sometimes just changing one or two assets can make a large difference.

Cheerio John

 

[fsbrown]

Poly Count

Thanks everyone, those replies cleared up a lot of questions.