Ground Projection: Corona vs. V-Ray

[kosso_olli]

V-Ray tries to preserve the way the dome light looks above the horizon so that the illumination doesn't change; it is still infinitely far away and doesn't have an actual radius. This is different from Corona where the dome light becomes actually a hemi-spherical light.

Best regards,
Vlado

Is there a way to adapt this behaviour? This would make scaling anything above the horizon line a possibility (a dream come true for me!)

[kosso_olli]

Just want to get back into this. Can the behaviour in V-Ray be improved to match Coronas output?

[JonasNöll]

I was just thinking maybe as a workaround it would be possible to create a sphere with a spherical UV map in the hdri as a LightMtl, then flatten out the lower half while maintaining a smooth transition to the horizon edge and then play with UV's and overall scaling of the object. At least that's how it looks what is happening in Corona to me. Not sure how the tripod height would be considered by this though.
Anyway I didn't notice how limited this V-Ray ground projection actually is before I tried out Corona. So I think making this work the same way like in Corona should be a priority as that is pretty standard task to be honest...

[kosso_olli]

Sure, that workaround is a solution. But it is not a good one, because it is much more work and does not support MIS.

[^Lele^]

Sure, that workaround is a solution. But it is not a good one, because it is much more work and does not support MIS.

Provided you don't use the probe for lighting, the absence of MIS strategies shouldn't matter at all, as the node is not a light.

So I think making this work the same way like in Corona should be a priority as that is pretty standard task to be honest...

I strongly disagree.
A fixed-size lighting fixture means lighting in the scene changes a lot when the feature is activated, which i find conceptually wrong.
Want a custom projection, make a custom projection.

[JonasNöll]

Hi, i get your point about the lighting in the scene would change. However from an artist perspective who just wants to put a model in the an HDRI environment that doesn't look completely warped it probably doesn't matter that much.
Wouldn't it be possible to use the current approach for lighting calculations and have an option for the camera visiblitly that offers some additional tweaks in order to make it look less distorted and this way more usable?
Do you also conceptually disaprove the way that Corona handles this task? It's also a Chaosgroup product, isn't it?

[^Lele^]

Hi, i get your point about the lighting in the scene would change. However from an artist perspective who just wants to put a model in the an HDRI environment that doesn't look completely warped it probably doesn't matter that much.
Wouldn't it be possible to use the current approach for lighting calculations and have an option for the camera visiblitly that offers some additional tweaks in order to make it look less distorted and this way more usable?

That's what an artist would do, now, would it not?
The tools are all there (properties, shaders, trace sets, compositing in-camera, etc.), it's been done manually for ages, i see no benefit in automation of such a thing.
Particularly as the number of possible permutations based on a projects/user's needs are nigh infinite.

Do you also conceptually disaprove the way that Corona handles this task? It's also a Chaosgroup product, isn't it?

They are essentially independent, and most surely they heed absolutely nothing of what *I* may think.
But yes, there are a number of things i don't like of a number of other products, AND of a few features we have.
It's part of my job to be critical.
The key is being able to argument constructively, and thoroughly, and to provide for actionable alternatives wherever possible.
I should hasten to add that i also admire many a feature others bring to bear, and that i often advocate for the implementation of something i think may work for us as well.

[Stefan_Laub]

i also thing the current is unusable as it distorts the model, in which use one wants that?

as 3d artist in archviz field at least the corona way is the only correct one, (if the light changes a bit is not so dramatic).
the main scene of this option is to put things in an easy way "into the hdri" not to keep the light same.

for the workaround: well then the full feature woudl not be needed, why make it at all?

in end- as it seems 2 different views on that problem depending on which industry you are in - it might be ideal to make the 2 projection options, for choice.
like a " keep light identical" check-box, or a "no not distort image" option to check.

[JonasNöll]

Hi, alright, that is an interesting perspective I respectfully disagree though, because for me personally it's not a very convincing argument that in theory one could build something comparable with a complicated workaround if other renderers can just do it out of the box. But maybe for others that argument may sound convincing, I don't know...

[^Lele^]

i also thing the current is unusable as it distorts the model, in which use one wants that?

But it doesn't.
It's a different type of projection, with a different aim to just a directly viewed background.
Want it as a background, project it on a hemisphere or plane.

as 3d artist in archviz field at least the corona way is the only correct one, (if the light changes a bit is not so dramatic).

The projection DOES change, and the shadows and lighting WILL change when you go from an infinitely far away source to one with a precise location.
That it should be dramatic or not is entirely dependent on the HDRI used.

for the workaround: well then the full feature woudl not be needed, why make it at all?

I am not sure i catch the polemic.
Projections (camera and geo-based) have been done since the day CG was born.
V-Ray is wholly equipped (and well production-proven) to allow the user any latitude in that respect.

in end- as it seems 2 different views on that problem depending on which industry you are in - it might be ideal to make the 2 projection options, for choice.
like a " keep light identical" check-box, or a "no not distort image" option to check.

The industry isn't the issue here.
Clean workflow is, in my personal opinion.
Your approach to the matter at hand (meaning: a checkbox) isn't quite how i see it: the number of practical permutations to the usage users will make of this is enormous.
And that's why there are *already* a metric ton of tools in V-Ray's arsenal to this effect.

[kosso_olli]

it's been done manually for ages, i see no benefit in automation of such a thing.

Oh boy, this could not be more wrong. There is a huge benefit for anybody involved in the visualisation of cars and products. It would make our life so much easier, and the output of our work much more convincing and believable.

[kosso_olli]

It's a different type of projection, with a different aim to just a directly viewed background.
Want it as a background, project it on a hemisphere or plane.

It is not only distorted in the directly viewed background, but in the reflections as well! Which is a major grief I have with this, because the reflections are often too big compared to the backplate the car sits in. The way it is done now is just half-baked.

[kosso_olli]

which i find conceptually wrong.

Why does it matter so much what you find wrong! Listen to users, not employees!

[^Lele^]

Why does it matter so much what you find wrong! Listen to users, not employees!

It matters only insofar as I am expressing my view, which i am however entitled to as a licensed forum user, nevermind as a Chaos Employee.

As far as a ground projection working right off the bat as *you wish* it to work, when the HDRI has not been captured with that intent, good luck.
It's a reprojection, in a space which wasn't meant to be.
The Corona one will work, sure, if you are fine with the constraints.
It's a sphere you need to manually reposition via the map controls, and as a discrete sphere, you WILL find yourself outside of it if the position of your camera allows it.
Animating a camera (or having more than one view to render.) means having to constantly adjust the *map* setting (center, radius and camera height from the projection floor. That means an expression and wire parameters. No biggie, surely.), lest distortion happens.

Now, an infinite sphere maintains your environment, and you can move through it, and look wherever you please (above the horizon).
All you need is to repro your HDRI to a floor geo, which you will adjust suitably to be a matte, and whatnot.
The floor meeting the dome at the horizon, you maintained the correctness of your IBL and got your undistorted ground projection.

I find our way *much* easier to set up and work with, under the most user cases.

Attached: Being outside the dome, which is however an environment map, and distortion of the map (and max UI showing settings where camera height mismatches the settings).
Lastly, the same map but in V-Ray, with an undistorted ground projection (sorry if i uploaded the wrong snapshot earlier.).

[kosso_olli]

As far as a ground projection working right off the bat as *you wish* it to work, when the HDRI has not been captured with that intent, good luck.

All, and I do mean ALL the spheres that we either get by the photographer or shoot ourselves, are captured with exactly that intent, yes.

The Corona one will work, sure, if you are fine with the constraints.

It's working beautifully for the stuff I do on a daily basis. Way better than in V-Ray that's for sure.

It's a sphere you need to manually reposition via the map controls, and as a discrete sphere, you WILL find yourself outside of it if the position of your camera allows it.
Animating a camera (or having more than one view to render.) means having to constantly adjust the *map* setting (center, radius and camera height from the projection floor. That means an expression and wire parameters. No biggie, surely.), lest distortion happens.

I agree regarding the animation. For that case, I'd remodel the environmant and project by hand. But I could not care less about animation, hardly do that.

Now, an infinite sphere maintains your environment, and you can move through it, and look wherever you please (above the horizon).

That's the thing I'm talking about: I have no control of the size of the HDRI above the horizon. As it is now, it is way too big. Always.

I find our way *much* easier to set up and work with, under the most user cases.

I believe you are the only guy with that opinion. For print work, where cars or procucts need to be integrated into photographed backgrounds, that is a huge load of extra work for something that needs 5 seconds to set up.

Lele, we are going round in circles. Many of us desperately need such a feature. Punto!
There's no need for the old feature to be replaced, but more options would save so much more time!

Also, Corona is not the benchmark for this. For me it is Vred, which offers loads of options for projection, even motion blurring the result correctly.
And one last thing: Vlado in some of the beta talks already said he had some ideas in his head on how to approach this. But this was before Next even...

Sometimes I feel the guys here at Chaos need to step off their high horse, because loads of stuff is done better and more comfortable in other engines.