Photon mapping and Vray area shadows.

[yog]

Is there any way to get photon mapping to work with vray area shadows ?

The problem is, if you set up a scene with hard Vray shadows, photon mapping for the secondary bounce (stored in the irradience map), with the primary bounce set to irradience map everything works just fine.
But if you switch to area shadows the photon map calculates as it did with hard shadows, but the irradience map calculates the area shadows in a slightly different place (possibly the centre of the area light volume). This creates a problem in that at best you get a ghost second bright/dark area, but at worst you get two different shadow/bright areas.

Any ideas ?

[vlado]

Are you using a direct light?

Best regards,
Vlado

[yog]

Yep, just one direct light lighting the whole scene.
I'm purposely making the scene difficult by just using one light.

[yog]

Here are two images to describe what I mean.

The first is my standard test scene with a single distant light set to hard Vray-shadows. The primary bounce is irradience map and the second bounce is photon mapping (with the option to save to irradience map).

The second is exactly the same scene except that area shadows have been switched on and given a U,V,W size = 15 and subdivisions=18. As can be seen the shadow is in a completly different place, even though the light itself has not been moved.

It might not be too obvious from the images, but close inspection looks like the lightspill seen on the soft shadow image where the wall meets the ceiling is the same as the reflected light from the wall onto the ceiling that can just barely be seen on the top hard shadow image.

As this is my test scene I have lit it in many different ways, and the only time I see this type of light spill is when I use photon mapping with soft area shadows

[twinxel]

Yog,

When you switch to Area Shadows, it works like was a spot- Try placing it far away from the target to see what happens...

Regards,
Joao.

[R2J2]

yog, theUVW size affects the "soft" shadows, higher values softer shadows and the distance form objects will affect the shadows, also your scene size will affect them, it's all relative.

[yog]

Hi guys.
Thanks for the comments,
Twinxel ; Good catch, that does look like what’s happening.

It's not the fact that the shadow changes position when area shadows are switched on, I could live with that, the problem is that the irradiance map seems to be taking it's light in a much different way than the photon map, producing two distinct lit areas on the ceiling. If Twinxel is correct it looks like although the photon map is taking it's light measurements from the original Direction light, the irradiance map is taking it's light reading from a pseudo Area/Spot light.

On looking at it again, it is either the irradiance map is gathering the light in a different way than the photon mapping, or that ALL the bounced light is being calculated from the standard Direction light, and ALL the direct light and shadows are being produced by the Area light (which is behaving like a spot light).
This might be why even though the direct light is missing on the right hand wall in the second image, the bounced light from where the direct light would have been is appearing on the ceiling immediately above it.