Matching Keyshot "Ground" to HDRI ground...

[Deacon]

I've just start experimenting with using HDRI environments in some of my renderings. Been using studio backgrounds up to this point and I can't seem to match Keyshot's ground level with the ground level in any HDRI images. Is there a trick to doing this or is it all done post rendering in Photoshop with backplate images? When I snap the object to ground, it's usually several feet above the ground level in HDRI images... very frustrating. Shifting the object using the Keyshot interface never seems to produce a believable result. What am I missing?

Paul

[JeffM]

Think of your object floating within a sphere, the HDRI is mapped to this sphere. In order to "ground" the object more firmly, try hitting the "g" key.This flattens the bottom half the spherical environment up to the ground level. It distorts the environment, but can look okay in many cases.

This "flatten ground" option can also be enabled in the Project>Environment tab under the "Advanced" setting at the bottom of the menu.

The best possible way is to combine a backplate with the environment.

[Deacon]

Thanks Jeff. I've tried the flatten ground option as well but it usually causes too much distortion in the image and when I change size and height to minimize the distortion, I don't have the background view I'm after. It appears to be a matter of getting the absolutely right HDRI background for the model being rendered. I'm looking specifically for an empty warehouse/industrial scene and the stock Keyshot Factory HDRI works quite well, but I've used it several times and am looking for a similar environment, yet something new. I have some excellent HDRI environments from Weiss but can't get the geometry to work properly in them at all, at least not yet.

I did make an interesting discovery though. I draw everything in Autodesk Inventor now, but several years ago I was using Ashlar Vellum's Cobalt. I've since imported and updated all my old Cobalt drawings in Inventor but have noticed that any drawing that started out as a Cobalt file is very difficult to position correctly in a photographic HDRI environment (the floor height is much higher), whereas any drawings that were completed exclusively in Inventor have a much lower floor height and are much easier to place correctly. So I'm thinking a large part of the problem may stem from original Cobalt geometry. 

Paul

[tsunami]

For me the best solution to get an appreciate goal, is:
_ use the hdri environment, playing with it , untill you can find a reasonable and a realistic model position, that could match with the ground-
_ then, hide the 3d model from the keyshot scene, and start the render; so you will get a render image of that position
_ use that image as backplate and the hdri environment as lighting, so u can have light and backplate matching.
_ turn on grid and 3d model on keyshot scene, and try again to match position. (if u have a car model, u can cut a bit the tyres so you will get realistic "weight".
Many of my hdri environment are with big size 200-300 Mb , so for to manage with them, u must have a decent pc memory and power cpu...
Regards

[Deacon]

Thanks for the tip Tsunami. That's actually the process I used for the two renderings posted elsewhere on this forum. After positioning the model, I rendered the environment without the model to use as a back plate. Then I reintroduced the model and rendered again with alpha and assembled the two renders in Photoshop. This allowed me to do some post production work in Photoshop on the model without affecting the backplate image. I was able to solve the ground issue through more careful positioning and using an environment with a more appropriate geometry.

Paul