Vray 1.5 SP3 - Volume caustics tutorial

by Francesco Legrenzi @ copyright 2009
www.francescolegrenzi.com




INTRODUCTION

VRay 1.5 SP3

In previous tutorial we explained how generating clouds with VRayEnvironmentFog, simply using atmosphere gizmo and procedural map. Creating volume caustics is easier. It's just necessary adding atmosphere effect and checking caustics, and VRaywill make the job.




Fig. 01-02 - Examples of volume caustics.

TUTORIAL


This short tutorial shows steps to obtain green shpere rendering.
Run 3ds max and set scene in cm, that will help us in understanding caustics setting units.


Fig. 03 - File units.


Now create scene elements: Plane, Standard camera, Geosphere and Spotlight.


Fig. 04 - Four elements in our test. Look at large plane size.


The "rock" is a dense geosphere with Noise modifier on.


Fig. 05 - Deformed Geosphere params.

Camera is a simple 3ds max Standard, while light is a slight modified Spot.


Fig. 06 - Changed Spot light params.


We won't use Global Illumination in this test, because we just need to understand how getting volume caustics. Adding GI will waste time. though not strictely necessary, set LWF here too.


Fig. 07 - Setting panels.

As we can see, many setting has been left as default. Main stands in caustics. Following settings in study scene.


Fig. 08 - Photon Map settings.

A quick explanation to simple params. You can find a caustics videotutorial here.

Multiplier: as standard light multiplier, increases or decreases caustics intensity. Makes them lighter, brighter. Modifying value won't request new PM calculation. In fact, once computed, it can be stored and used again, just like happens with IM and LC. to achieve physically correct results use 1, but feel free to change it.

Max density: figure Max density as a grid size. Lesser the value, denser the grid; we'll get better quality spending more photons for "clean" caustics. Smilar to radiosity rule, with high-divided meshes we get precise solution at cost of time.

Search distance: setted grid size, VRay computes and interpolates photons. Higher search distance value means more photons in interpolation algorithm; giving blurred caustic with definition loss.

Max photons: maximum photon number VRay uses to blur PM. If Search distance uses distance among photons, Max photons uses their number. Both can be modified without new PM computation.

Last important parameter for PM generating, physically defines photon number VRay uses in PM estimating. Since photon emitter is light based, last param is in VRay light properties.



Fig. 09 - Reach this panel following V-Ray properties, clicking right on selected Spot light. We use 2.000^2 photons.

Run render on a DualXeon Quadcore 3.2 ghz.


Fig. 10 - We get caustics in 9 seconds + 30 for PM.


Add VRayEnvironmentFog (VEF).


Fig. 11 - The volume effect.


See both volume light cone and volume caustics in render.


Fig. 12 - Last rendering, got in 59 secs + 30 for PM, necessary in VEF's checked.

If you want, you can use hidden VRay feature with maxscript:

renderers.current.caustics_showCalcPhase=false

In order to run progressive and high-precise caustics computation. A deeper explanation in my videotutorial.
Same rendering needing 12 minutes. First rendering shows pure volume caustics (reported timing is wrong), second final rendering.



Fig. 13 - Final rendering with progressive caustics.


Resulting caustics are very precise, but cause higher noise. rule is quite similar to PM and PPT.

Hope you are enjoy with my little tutorial. In attachment the video.
See the next time

Ciao

Francesco Legrenzi.
www.francescolegrenzi.com