Geometry based sampling in fast sss2 - in world units?

[joconnell]

Hi folks,

I've got a character which is using fast sss2 as part of a shader and I've started looking at the geometry based sampling as a method of getting quicker results. There's no documentation for it as of yet though so I wanted to get some clarifications on it. It's saying "samples per unit area" as it's quality setting and I was wonder if this was in your scene file unit or hard coded to centimeters as with other vray calculations? What I'm cautious of is that using automatic calculation seems to be quite slow for what I need, but will setting a samples per surface area cause problems for objects that travel from far away but end up close to camera? In other words will I end up using too many samples far away and not enough close up?

Cheers for any hints!

John

[Morbid Angel]

Hi folks,

I've got a character which is using fast sss2 as part of a shader and I've started looking at the geometry based sampling as a method of getting quicker results. There's no documentation for it as of yet though so I wanted to get some clarifications on it. It's saying "samples per unit area" as it's quality setting and I was wonder if this was in your scene file unit or hard coded to centimeters as with other vray calculations? What I'm cautious of is that using automatic calculation seems to be quite slow for what I need, but will setting a samples per surface area cause problems for objects that travel from far away but end up close to camera? In other words will I end up using too many samples far away and not enough close up?

Cheers for any hints!

John

I think this really depends on build version you are using. I've reported a few issues there, hopefully they were resolved. I had many issues using obj based sampling. But in new vray builds there is skin material which has new raytraced mode, gives good bang for the buck. You should give it a try imo.

[joconnell]

Still on 2.45 in maya land so no raytraced for me just yet. Geometry based is proving a huge amount quicker than not though. Back to max land in a few weeks and ideally up on to vray 3.

[vlado]

I was wonder if this was in your scene file unit or hard coded to centimeters as with other vray calculations? What I'm cautious of is that using automatic calculation seems to be quite slow for what I need, but will setting a samples per surface area cause problems for objects that travel from far away but end up close to camera? In other words will I end up using too many samples far away and not enough close up?

It is in world units. The whole point of object-based sampling is that it is not dependent on the distance to the camera, so there are no issues if you move close or far away.

Best regards,
Vlado

[joconnell]

Ah super - just a terminology thing for me then, since it's called "geometry based sampling" and the quality / accuracy slider was titled "samples per unit area" I wasn't sure if the unit area meant screen space or world units. Either way it's nice and detailed and rather fast!