[Sidefx-houdini-list] Shading artifact when really close to surface

Ivan DeWolf ivan at martian-labs.com
Wed Oct 21 19:24:35 EDT 2009


source this CMD into an empty session

render to IP, you gett a smooth surface.
zero out the translations on the null, you get floating point errors  
in the render.



Quoting "Andrew D Lyons" <tstexture at gmail.com>:

> Internally Houdini still uses floats (real) instead of doubles in many
> places - so I wouldn't think so.
>
> Doesn't putting big transforms in /obj nodes instead of transform SOPs
> improve/ remove certain distance related precision errors with certain
> renderers? For packages that flatten transforms, and don't feed
> seperate local and object space co-ordinates into the scene
> description (ifd/rib etc) precision errors like what Ivan is talking
> about can be a real problem, but I think Houdini gets around it if you
> use the obj node for your big transforms. Not sure if that wopks for
> the viewport though. OpenGL supports hierarchical transforms - so I'd
> hope so.
>
> Cheers
>
>
> 2009/10/21  <craigleehoffman at aol.com>:
>>
>>
>>
>>  Ivan,
>>
>> Do any of the precision problems improve if you move from 32 bit to  
>> 64 bit Houdini?
>>
>> Thanks,
>> Craig
>>
>>
>>
>> -----Original Message-----
>> From: Ivan DeWolf <ivan at martian-labs.com>
>> To: sidefx-houdini-list at sidefx.com; Francois Duchesneau <sidefx at trinix.ca>
>> Sent: Wed, Oct 21, 2009 11:19 am
>> Subject: Re: [Sidefx-houdini-list] Shading artifact when really  
>> close to surface
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> another problem you seem to have is floating point error.
>> Your are a couple of meters above sea level, but the center of your
>> geometry is at the center of the earth, thousands of kilometers away.
>> If you move your scene closer to the centroid, you will have fewer
>> issues.
>>
>>
>> To understand a bit about floating point error, put down a"box" sop
>> (in an empty scene) and hit space-g and tumble it. Nice and happy.
>> Now set it's X center to 1000000 and hit space-g
>> tumble and its all jumpy... and one more zero and tumble and it
>> doesn't even look like a cube.....
>>
>> in a computer, if you a really far from the origin and moving small
>> distances, you get floating point errors.
>>
>> The difference betweeen 1000000.036 and 1000000.037 is very different
>> from .036 and .037 in the computer....
>>
>>
>>
>>
>> _______________________________________________________
>> Perfection is achieved when nothing else can be removed
>> -Yvon Chouinard
>>
>> ----------------------------------------------------------------
>> This message was sent using IMP, the Internet Messaging Program.
>> _______________________________________________
>> Sidefx-houdini-list mailing list
>> Sidefx-houdini-list at sidefx.com
>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>
>>
>>
>>
>>
>> _______________________________________________
>> Sidefx-houdini-list mailing list
>> Sidefx-houdini-list at sidefx.com
>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>
>
>
>
> --
> =======================================
> Andrew D Lyons | Digital Artist | http://www.tstex.com
> =======================================
> _______________________________________________
> Sidefx-houdini-list mailing list
> Sidefx-houdini-list at sidefx.com
> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>



_______________________________________________________
Perfection is achieved when nothing else can be removed
-Yvon Chouinard

----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.


More information about the Sidefx-houdini-list mailing list