Ground Projection: Corona vs. V-Ray

[JonasNöll]

That's cool, so you can even get your reflection motionblurred correctly! Thx for the demonstration pics!

[kosso_olli]

Hmm, if I'm not missing something this tutorial just says: "Increase your ground projection radius", which doesn't give any satisfying results at all.

That's because Lele still did not grasp what this is all about. It is not the size of the ground projection (ie the lower half of the dome), it is all about the upper half of the dome. It is always too big, by a mile!

[kosso_olli]

Sorry, how do you do this with Corona on a box?

This is Vred, as described in the corresponding post.

[JonasNöll]

Hey, so can I send you the file and you demonstrate how to do it with your projection approach? I think for now I would be happy to just see the spherical hdri projected similar distortionfree like in Corona. Leave this box projection out of the question pls, I just want to have a distortion free spherical environment projection. No matter how complicated, just distortion free. Any approach is fine.

[^Lele^]

Yes, but
a) i find no mention of this in the texture projection options of VRed, so i'd love to see the source page (remember: it has to be actionable.), and
b) You mention Corona does this out of the box. This being the projection of the HDRI on a box, but perhaps you meant on a sphere.

What i see above is a cylindrical, capped projection on a box, with all the undue distortion that entails (check the parking lines as they meet the walls.). Standard UV work, no need for a camera, or ground projection.
I rest my case on there being some confusion, be it mine or yours, about what it is we're talking about.

[^Lele^]

Hey, so can I send you the file and you demonstrate how to do it with your projection approach? I think for now I would be happy to just see the spherical hdri projected similar distortionfree like in Corona. Leave this box projection out of the question pls, I just want to have a distortion free spherical environment projection. No matter how complicated, just distortion free. Any approach is fine.

I'm sure you can spend some more time with the controls to find the perfect match.
There is one, somewhere in the 3d scene, where there is no distortion.

EDIT: For example, see attached: dome and camera centered on the origin. Camera raised by 31.21 units from the ground.
Turn on ground projection, set radius (which should be labelled "height", admittedly.) to 31.21, voila'.
Undistorted ground projection.
Sample 2:Camera moved to [50,20,30] from its original [0,0,31.21], and turned to look elsewhere. Map updated accordingly (the Z is 0 because we use height.). Projection updated, and undistorted.

[kosso_olli]

Hey, so can I send you the file and you demonstrate how to do it with your projection approach? I think for now I would be happy to just see the spherical hdri projected similar distortionfree like in Corona. Leave this box projection out of the question pls, I just want to have a distortion free spherical environment projection. No matter how complicated, just distortion free. Any approach is fine.

Can you share it here? Would like to try whats possible.

[JonasNöll]

Great support, thx!
kosso_olli: Alright, will prepare somthing and give to you later

[^Lele^]

olli So, let me get this straight, you'd be fine with a way to offset the horizon line?
If so, turn on "crop/place", and set the V value to positive or negative to pull the horizon down or up, respectively.

[kosso_olli]

a) i find no mention of this in the texture projection options of VRed, so i'd love to see the source page (remember: it has to be actionable.), and
b) You mention Corona does this out of the box. This being the projection of the HDRI on a box, but perhaps you meant on a sphere.

Did these ages ago, but the tech is still valid.

https://knowledge.autodesk.com/suppo...html-html.html

Each of these can be scaled to your desire.




Regarding Corona: Yes, it only supports the spherical mode. But I have all the controls needed to get the proper size of the HDRI above the horizon line, whereas it is fixed in V-Ray.

[kosso_olli]

olli So, let me get this straight, you'd be fine with a way to offset the horizon line?
If so, turn on "crop/place", and set the V value to positive or negative to pull the horizon down or up, respectively.

No, no offset. That can already be done with the Crop/Place. A multiplier or something to control the scale of the HDRI above the horizon line is needed. That's what the radius in Corona is for, it is scaling the entire "sphere". The camera height in Corona is fine and correctly labeled, it does what it should: Define the origin of the captured HDRI above ground level (ie the height of the capturing camera on the tripod on set).

[^Lele^]

You could have linked the vred page to begin with, and saved me the teeth pulling.
Right, so it all boils down, for you (Jonas has other issues), to the projection being discrete, because you want to be able to project the spherical background on any geo.

That is *not* Corona's approach, rather in line with what i was saying all along: a projection *system* to do a specific task, instead of a toggle which makes unholy things to the scene.
In the process of developing one such system, Corona would get better too, likely.
Regardless, it's as i thought: it's not going to be simply copying Corona's.
The quest goal has already been moved further.

But let's be clear, this can be done now if you know how to use Max's own tools for projection and camera projection.
The setup is fairly reusable too, and allows for more latitude than any one-click solution ever could (f.e., reducing unwanted distortion just in the area we see.).
You could do worse, on a professional level, than getting familiar with it.

[kosso_olli]

Right, so it all boils down, for you (Jonas has other issues), to the projection being discrete, because you want to be able to project the spherical background on any geo.

No. All that is needed is a multiplier/value to tell V-Ray the size of the HDRI above the horizon.

Anything apart from that is nice to have, but not needed for our work. I will prepare a set of images to illustrate (again) on what this is all about.

[kosso_olli]

Post 1/2

Alright,
lets begin: Standard HDRI of a parking lot, common situation.


Insert teapot (radius 20cm) and VrayHDRI as background environment in default settings. The teapot is floating in space (not visible in this perspective) and is not sitting on the ground. Also, the scaling of the HDRI is too big.


Now lets activate ground projection with default radius of 1000. Teapot is now sitting on the ground, but the scaling is even bigger.


Now, adjust ground projection radius to 110 (110cm was the height of the capturing device of the HDRI on the tripod on set). Scaling looks okay.


Lets check scaling with reference from set. Distance between the outer edges of the marks on the ground was 250cm. The plane now is 240cm on the inside of the edges. Looks correct!



Please continue on post 2/2 on the next page.

[^Lele^]

No. All that is needed is a multiplier/value to tell V-Ray the size of the HDRI above the horizon.

We'd have to make the projection discrete for that to happen.
Which is not fine done through a map, and not fine from a lighting point of view, as explained.
And which is doable with standard UV mapping on an aptly prepped environment sphere.

Anything apart from that is nice to have, but not needed for our work. I will prepare a set of images to illustrate (again) on what this is all about.

Raising the stakes here is better than keeping them (seemingly) lower.
Mapping on complex geo is a problem worth tackling, as it applies to a number of tasks.
Maybe something novel can be brought to bear, then.