Motion blur subdivisions or samples?

[simmsimaging]

Now that I can get motion blur to work with Realflow meshes I'm trying to sort out the workflow. I've been testing for a few hours and been through many threads (and The Vray Complete Guide...) and I am still not clear on how the parameters interact.

I use the vray physical camera exclusively, so the mblur 'amount' is controlled through the shutter speed - no problem there, but I am not sure how to use the subdivision control along with the geometry samples to control speed/quality.

From what I can see you set the geometry samples for the physical camera in the camera tab of the render dialog (which seems odd - should be in the physical camera controls?) or per-object in the object Vray Properties. The per-object control overrides the global I think, but which subdivision control overrides the other? Is the one in the camera properties the one to use, or the camera tab in the render dialog?

My other question is what exactly do I control with subdivision rather than samples? Most of the threads talking about quality don't really mention the subdivision parameter, only the samples. It looks to me like subD controls the noisiness a bit more but I can't really get a good bead on what it is doing. Could anyone clarify?

Thanks in advance,
b

[vlado]

Geometry samples control how many "snapshots" of the mesh are taken to calculate motion blur; between these snapshots, the mesh movement is interpolated linearly. For objects move or deform in relatively straight paths, two geometry samples (one at the start, and one at the end of the motion blur interval) is usually enough. However for fast rotating objects, or objects that perform complex movements quickly, more geometry samples might be required to render it accurately.

For realflow in particular, there is no need to set the Geometry samples to anything more than 2 - realflow meshes are linearly interpolated between frames by default.

The "subdivs" parameters for the motion blur or on the other hand, control the "noise" in the result, and work pretty much identically to other subdivs in V-Ray.

Best regards,
Vlado

[simmsimaging]

Thanks Vlado
b

[vlado]

Here is a page from the help index with some examples:

http://www.spot3d.com/vray/help/150S...ples_mblur.htm

The page is somewhat old - it talks about Analytic sampling, but the rest of the stuff might be useful.

Best regards,
Vlado

[simmsimaging]

That does help - thanks.

A question about RF meshes though: is there any way to get higher geometry samples than 2 for the them, or is it a limitation of the meshes themselves? Just wondering about getting some of the nice curving motion blur lines for arcs of liquid and splashes. As it stands now it works quite well, but it seems you have to keep the amount of blur fairly low or the straight line thing shows up.

Thanks!
b

[vlado]

That would be a question for the realflow guys; it probably depends on what kind of information is stored in the RealFlow mesh file.

Best regards,
Vlado

[simmsimaging]

Okay - thanks.
b