Artifacts when using very large objects

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Artifacts when using very large objects

Hi,

I'm looking to create a scene where the earth is to scale (1 luxrender unit to 1km) and the sun is approximately to scale as well (in this case its proportionally closer and smaller than it should be). I had a fairly complex scene with high resolution textures for the surface of the earth, specularity, clouds and a scattering atmosphere etc working very nicely except that there were artifacts on the surface of the earth. I slowly removed textures and materials to see what was causing it and I couldn't find the culprit. Below are three renders, the first two done with different 0.9 weekly builds and the third with the stable 0.8 GUI version. I've included the code below.

Any help getting rid of these artifacts would be really appreciated.

Stuart

Lux version 0.9 (dev) of Mar 4 2012 at 16:48:22

Lux version 0.9 (dev) of Feb 4 2012 at 18:51:40

LuxRender GUI 0.8 May 29th 2011

Code: Select all
# Main Scene FileRenderer "sampler"LookAt -5374 5374 0 -5374 0 0 0 0 1Camera "perspective"   "float fov" [49.134342077604479]   "float shutteropen" [0.000000000000000]   "float shutterclose" [0.041666666666667]   "bool autofocus" ["true"]WorldBeginTexture "SolidColor" "color" "constant" "color value" [0.0 1.0 0.0]MakeNamedMaterial "SolidMaterial"   "texture Kd" ["SolidColor"]   "string type" ["matte"]AttributeBegin  #  "Earth"   NamedMaterial "SolidMaterial"   Shape "sphere" "float radius" [6378.0]AttributeEndAttributeBegin #  "Sun"Translate -1500000 0 0AreaLightSource "area"   "float gain" [30000000]   "color L" [1.0 1.0 1.0]Shape "sphere" "float radius" [3189]AttributeEnd # ""WorldEnd
stugrey

Posts: 4
Joined: Mon Mar 12, 2012 4:56 am

Re: Artifacts when using very large objects

You're using a sphere shape. Have you tried a triangle mesh instead?
Linux builds packager

SATtva

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Re: Artifacts when using very large objects

Hi,

There was an issue in the latest build regarding one method of the sphere shape. The issue has since been fixed, but no new build has been issued yet.

Jeanphi
jeanphi

Posts: 6570
Joined: Mon Jan 14, 2008 7:21 am

Re: Artifacts when using very large objects

Here are the results with the triangle mesh, it seems to be showing exactly the same sort of artifacts. Any other ideas?

Lux version 0.9 (dev) of Mar 4 2012 at 16:48:22
stugrey

Posts: 4
Joined: Mon Mar 12, 2012 4:56 am

Re: Artifacts when using very large objects

stugrey wrote:Any help getting rid of these artifacts would be really appreciated.

It is probably better to set the Epsilon value by hand (i.e. the heuristic used for choosing the epsilon value is probably fooled by the scale of you scene).

P.S. the epsilon value can be set with command line options, for instance: http://www.luxrender.net/wiki/Luxconsole

Posts: 4795
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Location: Italy

Re: Artifacts when using very large objects

Thank you very much for your response, i've tried playing around with the epsilon values and it does make a difference

Lux version 0.9 (dev) of Feb 4 2012 at 18:51:40 - minepsilon = 100

I really didn't know where to start so I used trial error and picked a minimum epsilon value of 100 and it seemed to work. The problem is this value of 100 produces other weird effects in my full earth render. Does any one have any rules of thumb for epsilon values for a given size of scene and minimum level of detail required? What should I set the maximum epsilon value to?

Thanks,

Stuart
stugrey

Posts: 4
Joined: Mon Mar 12, 2012 4:56 am

Re: Artifacts when using very large objects

stugrey wrote:I really didn't know where to start so I used trial error and picked a minimum epsilon value of 100 and it seemed to work. The problem is this value of 100 produces other weird effects in my full earth render. Does any one have any rules of thumb for epsilon values for a given size of scene and minimum level of detail required? What should I set the maximum epsilon value to?

For a scene of a 1 meter, using an epsilon of 0.0001 usually works fine. Given the scale of your scene, you have probably to use a larger epsilon, have you tried to use 1000 and 10000 ?

P.S. keep in mind that the larger resolution of floating point numbers is between 0.0 and 1.0. Instead of changing Epsilon , you could just scale down all your scene (i.e. by 1,000,000 factor).

Posts: 4795
Joined: Sat Apr 19, 2008 6:04 pm
Location: Italy

Re: Artifacts when using very large objects

My scene was originally scaled down by a large factor but I thought i'd see how it worked at its true scale. I didn't even consider the floating point precision issue. I've now scaled everything back down and the only errors remaining are hopefully down to the sphere method error which is hopefully fixed in the next build.

I'd like to thank everyone for their help.

Stuart
stugrey

Posts: 4
Joined: Mon Mar 12, 2012 4:56 am