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<br><div><div>On 22 Oct 2008, at 10:04, jeando wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"> <font size="3">Hi,<br> <br> We are building an artificial sky for an architecture school where we teach, and before starting we prepare a Radiance model, to simulate the interior of the artificial sky. The idea is to help us to choose the right bulbs, the ceiling, etc.</font></blockquote><div><br></div><div>Interesting approach. I would have used physical mock ups to decide on</div><div>materials (diffusers, layout and spacing) and measurements on a number</div><div>of lamps of the same type to check for manufacturing inconsistencies.</div><div><br></div><div>With Radiance you introduce the new complexity of modelling the</div><div>physical materials _correctly_ in a virtual world and in some cases</div><div>you have to deal with the optimisation of the algorithms. </div><br><blockquote type="cite"><font size="3">To simulate the overcast sky (Moon and Spencer) distribution in Radiance we made walls of mirror material and ceiling is filled with fluorescent tubes (very close to one another) and covered with translucent material. Then we tried to render few images of interior, with several sets of rendering parameters, but final images still aren't good enough with a lot of spots.<br> <br> Please see our results on <a href="http://docs.google.com/Doc?id=dfvbdbg3_13f66n99kx">http://docs.google.com/Doc?id=dfvbdbg3_13f66n99kx</a></font></blockquote><div><br></div><div>At a first look I'd say your spotty images are the result of "-av 0 0 0" and a rather low</div><div>"-ab 4". Note that the trans material will swallow one bounce just to let light pass. That</div><div>leaves you 3 bounces to hit a light source which is not a lot.</div><div><br></div><div>As a first step I'd set "-av" to something realistic. You should be able to calculate a</div><div>reasonably good approximation of the ambient value from your physical set up.</div><div><br></div><div>Next: Your rendering times might benefit from an 'illum' calculation. Replace the</div><div>"trans" material ceiling with an "illum" to make it a direct light source. This will affect</div><div>the appearance of the ceiling but not the accuracy of the rendering. However, this</div><div>may go against your idea of simulating the physical set up.</div><div><br></div><div>In your last image you're disabling the ambient cache with "-aa 0". Now every</div><div>ray is calculated with your high settings. You can probably reduce "-ad" and "-as"</div><div>a lot in your uniform environment. I'd also set "-lr" back to 8 again. There is a</div><div>difference but it has not such a big visual impact.</div><div><br></div><div><br></div><div>Regards,</div><div>Thomas </div><div><br></div><div> </div></div></body></html>