HDRs, ground plane, shadows and reflections


Of course, I know you are working on this, still I’d like to give some more feedback… (Which is just, because I am curious and would like Cycles to be cool in 6 weeks instead of 12. Or so.)

Large HDRs seem to no longer crash Rhino immediately, but light and shadows, when using them, still just look like not right. (Though I couldn’t describe that “right”…)

When e.g. a pretty low sun comes from west:

I get this:

The result looks quite nice, but the shadow is too short and too soft.

When I use “Show shadow only” for the ground plane (to get rid of the horizon), it looks like the white reflection from the second image turns into a shadow or too dark reflection and on the right side I am not getting any shadow at all:

And when I then “Reset To Defaults” the shadows/reflections are the same for intensity 0.5 and 1.0. I just used a color picker tool to check that, but they both seem to have the same range. (In the second image here I just changed the default Studio’s intensity to 0.5…):

(Nathan 'jesterKing' Letwory) #2

If you are using skylight in conjunction with sun the shadow will currently be not very pronounced. Does the shadow (length) look better when you turn of skylight?

I added RH-39192 so we can track this

This is to be expected. When you set the ground plane to be shadow only it no longer contributes diffuse light to the box. This has quite a big effect on how objects will render.

Through the ground plane with shadows only set you’ll see the background. By default the background is set to solid white, hence you see solid white here.

Using defaults means shadow only ground plane. The shadows have the same effect as the lighting on the cube. They are attenuated, but not colored. With a ground plane that has i.e. the default material set you’ll see the shadow result to be much darker for different intensities.


For all images I used a HDR that has a sun in it and didn’t use Rhino’s sun at all…

But I’ve decided to learn a bit Blender now to have a look at things there.

(Nathan 'jesterKing' Letwory) #4

Note that currently for skylighting a heavily downsampled (all the way down to 64x64 pixels) and blurred version of the HDR is used. This means that small details like the sun don’t contribute as much.

Rhino WIP (6.0.17122.11501, 17/05/02) crash switching to Raytraced with CUDA, and how to FIX

Then, not too surprisingly, HDRs are nothing more than some light atm…

Okay, I thought it was like some shadow catcher thing. When using Cycles in Blender a ground plane that is marked as shadow catcher also, as I was expecting, contributes diffuse light. (The final render then contains the “catched shadows” while ground plane is removed…)

(Nathan 'jesterKing' Letwory) #6

Hi, reviving this old thread as I’m ploughing through my bug list.

The HDRs are no longer downsampled, haven’t been so for a long time. You should be able to get pretty clear shadows from HDRis that have a small, intense light source embedded. Larger will be obvious too, but with less sharp shadows obviously.

The bug report for this was https://mcneel.myjetbrains.com/youtrack/issue/RH-39192

@MarcusStrube, can you confirm you can get better shadows from HDRis now?

Here a quick sample with the Met Balcony NYC environment that comes with Rhino. Skylight lighting only, no other lights nor sun.