Easily determining position of HDRI light source in scene

[sduck]

If you want to be able to align them very accurately you could try my approach:
1.With your VRAY sun, render an image with a 2 to 1 aspect ratio (ex. 360x180) that uses a spherical camera with a FOV of 360 (Best not to have a shift in your camera settings or it will distort the image).
2.Turn off your VRAY sun and load your HDRI image and render a second spherical image.
3.You now have images of both of your sky types. Bring each into Photoshop and determine there sun's exact placement. If the image is 360pixels wide with a 360 degree FOV then 360/360= 1 degree
4. Each pixel is 1 degree. Count the pixel difference of your suns and go back to 3DS Max and rotate your HDRI exactly.
5. Just for verification rerender your spherical HDRI map and compare with your original VRAY sun image. You can get them dead on.

[chriserskine]

I do this a little differently and its really quick.

I apply hdri to a sphere. and switch between a standard map and vray light material. so i can see it in the viewport to align it. then render with the light material.

to get the mapping right i use uvw unwrap. and then leave it all as default settings. this work's perfectly with a equirectangular hdr's. (no distortion at top and bottome like you would get with sphereical mapping).

I've done some testing between vray dome light and this method and it dosen't seem to look any worse and much quicker to align everything.

[Guest]

I have just tried to locate my sun in the viewport background by moving the camera target and the viewport background doesn't move, its static. I'm using Max 2010, it works fine in Max 2011. Any ideas why this is happening?

[flino2004]

my mathematic way to do it is very accurate....usually spherical HDRI skies in the market have the sun in "x" right in the middle so you do need "Y" distance to get the correct azimuth.
open it in photoshop pick the center of the source then you will get the pixel in Y(amount of pixels from the bottom of the HDRI)...let's say that the dimensions are 7000*3500(HDRI) then Y*90/3500= Azimuth
now you can match a vraysun with your hdri and link them...if you need more shadow definition increasing vray sun will do the trick. pg tutorial shows how link both and how you can control them together.

http://www.peterguthrie.net/blog/201...-sky-tutorial/

Fernando

[peterguthrie]

I've been meaning to work out the math for a while... thanks fernando!

[flino2004]

Peter....Thanks to you for such great HDRIs (I purchased several of them BTW)

Fernando

[flino2004]

Actually after revising what I did the formula was Azimuth=Y*180/H where H is the Height of the image, the reason why I wrote Azimuth=Y*90/H is because I cut the black part of the HDRI(only to get Y) so if you take the full size it should be 180.

Fernando