is it possible to render an accurate sun-shadow study with Vray?
I know you can use the Sunlight system to get the appropriate sun angles. But i want to be able to accurately control the intensity of the sun and sky to get fairly accurate light values (color values of the sun and sky would be nice too).
i thought i read some time back that the daylight system didn’t work with Vray - is that still the case?
Viz sunlight system doesnt work good with Vray, but you can link a standart direct light to it…
Gonçalo
Does this apply to MAX sunlight system as well?
No, because with max sunlight system you can play with the light multiplier, not like with Viz where you cant lower it to values less than 50…
Gonçalo
but MAX actually has both systems - the SUNlight system, and the DAYlight system (the VIZ system that Goncalo was reffering to).
i am not sure what you meant when you said you can’t decrease the value below 50. with the Daylight system, you can switch it to manual and change the values - its just that the values use physically based units (lx) and not the standard MAX multiplier value.
I mean in Viz Daylight system if switch to Standart direct light for the sun I cant lower the intensity to less than 50…
Gonçalo
will it not work if the Sun is set to IES Sun?
In MAX, i just did what you said - switched the Daylight System from IES Sun to Directional Light - and i AM able to change the multiplier value (i also had to switch the ‘Position’ setting to ‘Manual’
okay. i AM getting the DAYlight system to work in MAX.
I switched the Position to Manual, then lowered the Intensity to about 2800lx.
The problem seems to be that Vray doesn’t analyze the ‘lx’ units for the light properly. The accurate lx value for the sun around midday is something like 96,000. With that setting, Vray renders everything blistering white.
so, in the end, i guess the answer to my question is - no. I can’t accurately render the intensity of the sun as it changes from morning to night with Vray. it breaks my heart to have to go back to MAX radiosity and 200MB MAX files to get my accurate sun-shadow studies.
sean
Sean, you can play with VRay’s color mapping to bring a washed out image to normal color ranges for example by lowering the bright and/or dark multipliers.
Best regards,
Vlado
if i use the default daylight system setting. i can’t get anything to read clearly by just changing the color mapping values. a couple samples:
exponential dark=1, bright=1
exponential dark=.2, bright=.2
Dont play with both at the same time, and also try exponencial
Gonçalo
i tried a whole bunch of different combinations (changing one at a time, or both, up or down, using exponential) but i still couldn’t get a decent rendering.
the only way that i got it to work was to switch from the preset values for the light to the manual setting - and adjust the intensity value myself.
Shame on me 
I ve played again and it woks with Viz too…
I was manage to get good results with color mapping at 0.025 for both, using IES Sun and vrayshadows and Date to time location, without skylight better with Vray Skylight…
Gonçalo
sweet! that is working for me too! i notice that ‘exponential’ does not work at all - color mapping has to be set as ‘linear’.
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curious what your settings are. i like to see more definition in the shadow part of my renderings. but, i am having trouble getting it bumped up. i already have my skylight (vray skylight) jacked up to 20. increasing the dark mutliplier doesn’t seem to affect it at all.
thanks for the help!
sean
i gave it a shot.
looks nice. can you post your settings? i’m curious what you used for skylight and irrad. settings.
Psy, if you use area shadows on a directional light, vray turns the directional light into an area light (sphere or plane), so you’ll need to move your lightsource very far away from the model to act as the sun. Otherwise you have non-directional shadows as in your image, with too much blur on them.
flipside
Hi to all
and thanks for the tips !!!
to PSY :
can I know wich kind of shadows did u used to get this soft shadows outline?
Bye and thanks for this great forum
Isn’t the size field (U, V and W) meant for this. Instead of moving the light out far away, can’t you just make it smaller?
Could be that the relative size of the scene makes it impossible though, and then the only option would be to move it further away.
But to have directional shadows (=parallel shadow lines) you need to place it far away. The closer you place it, the more the shadows edges diverge from each other. The sun is of course also not a directional light, but because it is so far away, it looks like the shadows are directional. It casts area shadows but only subtle. So If you don’t want soft edges for your sun shadows, just use directional light without area shadows and place it as far or as close as you want. But to have a little bit softshadows, use the area shadows option and move your light further away to create directional looking shadows again.