Hi,
I trying out an outdoor scene with physical sun, but I’m a bit confused about if I should use GI or not? And if I should, then what’s the correct way to set it up?
I hear Maya users debating about if it’s needed or whether using FG with multi-passes would do the trick. There’s also discussing about using the bbox parameters to guide the photons more precisely (I guess?) - but I can’t find this parameter anywhere in XSI.
Basically you just set up the sun/sky system, turn on FG and you’re done. Fiddle with the FG settings to get the look you want. Be sure to work with a tonemapper or the linear workflow settings too.
Also, have a look at Zap’s blog, there’s a lot of info on the latest shaders etc. as well.
It’s mentalraytips.blogspot.com
The bbox values are hidden in the PPG. If you would open up the PPG and scroll through the text, you would find them there, (and some other ones for that matter) set to 0.
The HTML manual has this to say:
When photon_bbox_min and photon_bbox_max are left set to 0,0,0 the photon bounding box will be calculated automatically by the shader. If these are set, they define a bounding box in the coordinate system of the light within which photons are aimed. This can be used to “focus” GI photons on a particular area-of-interest. For example, if one has modeled a huge city as a backdrop, but is only rendering the interior of a room, mental ray will by default shoot photons over the entire city and maybe only a few will find their way into the room. With the photon_bbox_max and photon_bbox_min parameters one can focus the photon emission of the mia_physicalsun to only aim at the window in question, greatly speeding up and enhancing the quality of the interior rendering.
automatic_photon_energy enables automatic photon energy calculation. When this is on, the light source does not need to have a valid energy value that matches that of the sun (it does, however, need a nonzero energy value or photon emission is disabled by mental ray). The correct energy and color of the photons will be automatically calculated. If this parameter is off, the photons will have the energy defined by the lights energy value.
So with the default settings, all ‘proper’ values are set already.
Hope this helps,
rob
Have a look at this thread as well. Great plugin to setup the physical sun and FG in a few clicks. All with HDR.
http://forums.cgsociety.org/showthread.php?f=24&t=674920
Regards.
Thanks for the replies,
Vauric, I’m actually using sIBL already, which is actually something that I first heard from Rob (so, thanks, Rob 
)
sIBL is great and I get a decent render with just the default FG settings - it’ just that I want to find out if there is a way to get even better renders and what are the optimal settings for those.
So far I’ve tried (apart from the defaults) setting GI on and as I didn’t seem to get any results using the physical sun, I set up an extra light source to shoot the photons. But it didn’t really change the image very much.
Now, I’m trying to set up IRP (which of course disables both FG and GI) in the same scene and just got the first render out - it looks nice, but is considerably darker than the ones with FG (including GI or not).
While experimenting is fun, it’s good to know which combinations are actually useful, because each try takes about half an hour on my machine
select the pass you want, initialize the physical sky and the only thing will do will put the Mia physical sun sky shader in the pass, then, the light you set up to be the sun, you need to connect in the material editor the sun node into it. will start with #1 and you seen will look all white lower it to .1 or .01 to start cheeking how does affect your scene,
be care full with the shadows and render times =).
Hi,
I don’t think I recorded any of the original render times, but I will render some more in the near future and I’ll try to remember to post the times back here. The project has been in the background now for couple of weeks, I should get back to it soon.
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