Hi Everyone,

I’ve been using mental ray for quite some time, but I don’t really understand what Final Gather is from a theoretical stand-point.  From the literature I have read, I understand it as some sort of Radiosity implementation?  Am I right in thinking that?  What exactly is Final Gather “gathering”?

I’ve read up on this, and I just don’t have solid framework of what it actually is.  Any clarification would be great!

Thanks!

I think it snds a ray, splints in 3 then it calculates colors around and bla blah.

Your correct it is a form of radiosity originally created to fake Global Illumination. Along with Ambient Occlusion

I believe they actually employ different techniques.

click on the link

click on the link

Also search for each topic in the Help, it too describes some of the methods employed.

if im not mistaken he asked about final gather, not GI…

LazloHollyfeld - 07 May 2008 11:21 PM

I’ve been using mental ray for quite some time, but I don’t really understand what Final Gather is from a theoretical stand-point. 

Final Gathering shoots a bunch of rays from the shading point to surrounding surfaces, to basically “measure” the irradiance at that point. This is normally not calculated for every shading, but calculated at “FG points” in a pre-pass and stored in a map called the FG map (what many others call an “irradiance map"). At render time, the map is looked up and the values from nearby points are weighted to figure out the indirect irradiance at a given location.

LazloHollyfeld - 07 May 2008 11:21 PM

From the literature I have read, I understand it as some sort of Radiosity implementation? Am I right in thinking that? 

Not at all. Radiosity is a particular form of indirect light transport. Final Gathering is also a form of indirect light transport, but fundamentally different to Radiosity.

Some people, though, confuse the terms a lot, thinking “Radiosity” simply means “Global Illumination” sort. It’s just one type.

LazloHollyfeld - 07 May 2008 11:21 PM

What exactly is Final Gather “gathering”?

Irradiance (by hemispherically sampling radiance)

The name comes from the fact that the “original” algorithm “gathered” it’s radiance measurements from a photon map. Nowdays you don’t “need” the photon map, because FG can “gather” the irradiance measurements from the direct shading of the point, also with multi-bounce.

/Z