Compositing shadows on top of grass

Hello everybody! :cool:

I’m making this short simple scene in which a UFO lands on top of a grass field. I have the compositing pretty much figured out so that the UFO casts a shadow on top of the field, which in my scene is represented by a flat plane with some minor height displacement to match the terrain elevation.

Now, here’s the problem. The shadow cast by the UFO on the grass field is too sharp, killing the realism. I would like it so that the shadow had jagged edges as if it were really cast upon a grass field and not onto a flat plane. I thought this would be easy to solve - I set up a hair particle simulation coming off the ground and tried to match the grass in the picture as faithfully as I could, with vertex groups controlling the height of the grass and whatnot. But I can’t figure out how to make it so that the grass doesn’t cast a shadow on the plane and on itself, causing my current compositing setup to fail.

To sum it up, I would like the grass field to receive the shadow cast by the UFO, without itself casting a shadow. Thank you so much in advance to anyone who manages to shed some light upon this subject, as I have looked everywhere and can’t figure out a solution.


Save yourself a world of digital heartbreak and just cheat the shot! Add a little bit of blur to the saucer’s shadow and call it a day. (If you wish, take the shadow as a mask and “alpha-over” the background onto itself within that shadow, so that the grass is a little more pronounced.)

Or… not. The simple reality is that the audience is never going to care, one way or another, as long as they are anxiously-awaiting the discovery of just what sort of Evil Alien is about to pop out of that saucer.

And, if they won’t care, neither should you. You’ve got a deadline to meet.

Remember that Star Wars Episode One shipped to theaters with a scene in which “a crowd at a podracer race” actually consisted of … colored Q-Tips™ cotton swabs. And no one noticed, until a “making-of” book revealed the trick. (It was subsequently changed on the DVD.)

So, yes: “if The Show™ is good, you can get away with murder.” Therefore, focus on The Show,™ and let the shadows take care of themselves. Since you do get to “choose your targets,” at least some of the time, choose wisely.

Sure but you shouldn’t have anything to distracting either. As sundialsvc4 suggests, just dial back the effect until you get away with it. Honestly I would be more worried about the space ship materials first as they are a bit of a give away too.

You could also simply displace the ground plane that the shadow is being cast on. It’s not perfect, but it’s better than nothing, and it’s easy.

Without displacement:

With displacement:

@hype is a show off! :wink:

Cool trick, but you need some green grass reflected back onto your ship :stuck_out_tongue:

hahahaha, so does the original poster! :wink:

The shadow under a spaceship … or, as the case may be, under a flying dog’s-toy … is one of those details that are “to be expected, but not important.” You might (or, might not) notice that it was not there, but you’d give it a second glance only if you’re a CG-nerd. :yes: Unless some plot-point causes the audience to be looking directly at it and paying attention to it, you could pretty much get away with anything, and you should probably strive to get away with as little as possible.

Hi guys,
thank you all very much for your suggestions. I ended up going with what you suggested and not caring about the shadow too much. I blurred it and added a displacement to the terrain as hype suggested. Looks very convincing and it’s a much easier solution.

Thanks again.