Tesselation factor

Any issues, problems or troubleshooting topics related to the Prepar3D client application.
pilotter
Posts: 22
Joined: Tue Nov 26, 2013 2:39 pm

Postby pilotter » Sun Nov 02, 2014 8:00 am

Good day, by reductiegetal the tesselation factor to medium, I have reduced the stutters. Could you tell me what this setting does?

Using gpu for scenery mesh , why we still have the mesh slider then?

Or for something else?

Or à other wat to ask; does a higher setting for scenery mesh has influence on the tesselation factor load to the gpu?

I have à 780gtx classified, and fsglobal ultimate mesh.

Saul
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Location: Manchester, UK

Postby Saul » Sun Nov 02, 2014 8:47 am

There are 2 sliders effecting meshs.
The Mesh slider adjusts the fidelity of your installed mesh.
Tessellation add extra fidelity to meshes.

Hope that helps you figure things out.

pilotter
Posts: 22
Joined: Tue Nov 26, 2013 2:39 pm

Postby pilotter » Sun Nov 02, 2014 9:05 am

Thanks Saul, not really sure what you mean by fidelity?

But what would iT do when you already have à 5m mesh? Also does it use the gpu?

Saul
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Joined: Mon Mar 04, 2013 1:02 pm
Location: Manchester, UK

Postby Saul » Sun Nov 02, 2014 9:31 am

Tessellation will make a 5m mesh setting appear to be 4m or 3m or 2 m.. depending on the setting.
Yes it is handled buy the GPU

pilotter
Posts: 22
Joined: Tue Nov 26, 2013 2:39 pm

Postby pilotter » Sun Nov 02, 2014 3:06 pm

So basically with mesh settings at 5 m I can switch of tesselation factor, and use it for other sources in p3d served by gpu? Or Will I Miss something?

filippo1974
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Location: North east of Italy

Postby filippo1974 » Tue Nov 04, 2014 9:01 am

The tessellation is a feature that basically adds polygons to a mesh, and is managed by the GPU. Using the tessellation, a mesh appears having more polygons than it had originally, thus giving the feeling of more "fidelity". It is basically the same method that You may apply to a picture to make it larger, by adding extra pixels via interpolation.
Adding more polygons to a mesh does not add detail to that mesh, since details that are not there originally can not be created from nothing; anyway, the tessellation helps make the mesh smoother.
If you have a highly detailed mesh, you might spare some GPU power by turning off the tessellation.

Regards,
Filippo
ATPL frozen - CPL/IR ME
P3D v4

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Beau Hollis
Lockheed Martin
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Postby Beau Hollis » Thu Nov 06, 2014 12:48 pm

Actually, your mesh resolution is still the max you will see. If you select 5m, 5m is the highest resolution you will get. The tessellation factor at max would basically force your mesh to be at the highest resolution. If you have a lower tess factor, you may get 10m or 20m points even though you're settings loaded a 5m mesh. This would only happen though if they 5m mesh tiles was far enough away. The GPU terrain does dynamic LOD calculations to determine how much of the mesh you need for a given scene. The threshold it uses to do the LOD calculation is the tess factor. You still get the basic LOD enforced by your LOD radius which determines how many tiles of each mesh LOD to load. The main difference is that even at 40,000 ft you are still loading those high-res 5m tiles directly below you even though you'd never be able to tell without looking down and zooming way in. That's where the dynamic down-res of the mesh can help out.
Beau Hollis
Prepar3D Software Architect

pilotter
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Joined: Tue Nov 26, 2013 2:39 pm

Postby pilotter » Thu Nov 06, 2014 1:50 pm

Thanks Bholis,

so If I am correct ( this is not so easy ) If I put my mesh slider at 5 meter but the tesselation factor at medium nearby I will get 5mtr but further away I will get 10 or 20 mtr.

If this is the case, could you tell a little more about this radius and what kind of factor this tess slider is using?

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Beau Hollis
Lockheed Martin
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Postby Beau Hollis » Thu Nov 06, 2014 5:26 pm

The LOD radius is a bit complicated, but there have been lots of forum posts and blogs about how it works, so I won't go into too much detail. Basically it just sets a radius in tiles ranging from 2.5-6.5. Terrain tiles are loaded in within that radius at a given LOD and then tiles 2x as big are also loaded in at that radius. The distance is taken without factoring altitude. The tessellation shader has more info to work with because it knows how big a tile is on screen based on its distance and the camera zoom. Thus if a tile is further away it can be drawn at lower detail. This done in the non-tessellated terrain and in FSX as well, but its done on the CPU and meshes have to be reloaded when the mesh LOD changes. Explaining the exact effects with match is a bit complex. I'd say just tweak the sliders to until you get a good performance/quality trade off. The tessellation factor is more noticeable in mountain scenery. Setting it too low will make mountains more jaggy and cause a bit more LOD popping.

Thanks
Beau
Beau Hollis
Prepar3D Software Architect

pilotter
Posts: 22
Joined: Tue Nov 26, 2013 2:39 pm

Postby pilotter » Fri Nov 07, 2014 6:09 am

Thanks Beau,

I will try different settings.

Rick


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