Casting onto a roadway.
Here's a still:
OnHDV.com/BlueTruck.jpg

Thanks.

I've used drop shadows (in track motion) with nice results.

Bo

Shadows are cast by the 3D shape of the object projected onto the 3D shape of the subject.
You can build a rough 3D model of the object in a 3D app, build what you want to cast the shadow onto and extract the shdow with apha and composite the whole thing in Vegas. There are applications out there specifically designed for these tasks, for example a CGI plane onto a landscape.

Bob.

Used Mask Generator and Track Motion.
Uncheck / check the Mask Generator on track 3 to see the 3D plane.
While the truck moves toward you add keyframes and adjust to match
the "virtual" angle of the ground.

You might need to blur track 3 to make it more realistic.

Who says you need more than Sony Vegas?

EDIT: if you background is more complex, then you will need a 3D app
to simulate the subject as Bob stated. You said audience, so the subject
may need bumps for bodies. I use Caligari Truespace but is rather hard
to get the hang of it. IF this scene is not too long your viewer may not notice.

IF this scene is not too long your viewer may not notice.
===============================================

I'd extend that a bit if I may.
You don't need a major CGI / 3D render, if the shot is quick and you can at least get the shadows sort of looking like they are part of the scene using simple 3D tools like TrueSpace or Bryce.
It takes the brain a few seconds to do detailed analysis of a scene, if there's nothing really jarring in there you can get away with blue murder.
The app I was looking at for doing this was used in The Aviator. The plane was CGI but the landscape was a real aerial shot. To create the shadows they just built the terrain using geodisic data, totally ignored all the buildings etc. For a light source, well they knew that date and time of day shot was taking so positioning the sun was easy. Now I doubt anyone watching the movie noticed their shortcuts yet looking at it frame by frame I'd bet you'd pick it straight away. I think one of the tricks in this trade is knowing what visual elements matter and what don't.

Bob.

Couldn't you create a copy of the truck footage, invert and distort it, add blur and change the color to black and make a shadow that follows every move of the truck perfectly? I guess that would assume that the background could be another color than black.

"Couldn't you create a copy of the truck footage, invert and distort it, add blur and change the color to black and make a shadow that follows every move of the truck perfectly? "

Yes, that's what I was hoping to do. Following the thread on "fire/flames" there was an example (in a different editing NLE) of making the shadow created by the blast by using exactly your suggested technique. In that example the point of initiation of the blast stays fixed on the screen.

The problem I've encountered with this event is that the truck doesn't *just* get larger in the event, but is seen moving from upper screen as a smaller truck to the middle as a huge truck. Thus there has to be some track motion, and the center of image is not fixed to a point on the screen. "Flipping" the event puts the "original" truck at the top, but the "flipped" truck at the bottom of the screen. Thereafter the shadow "converges" on the truck.

Time span is three-part as follows:
(a) 3 seconds when the truck is small and at the upper part of the screen while the audience is "jogging" on a road. A bicyclist comes from behind-right-screen and cuts in front of the audience (screen right-to-middle-to-slightly-left-of-middle while moving away). The truck (under which I painted a 70% cookie for a shadow and track-motioned it to match the truck movement) starts out as a distant hint down the road. The difficulty within this 3 seconds is that the bicyclist must block out the distant-but-approaching truck and then the truck and its shadow have to emerge from behind the bicyclist as the truck gets larger and the cyclist gets smaller. In the first second, even stop-framing does not expose the shadow trick and is quite believable. The emergence of the truck from behind the cyclist is where it gets tricky to move and shape that ever-growing shadow without wiping out some of the cyclist - especially considering the length of shadow at that time of day (late afternoon) requires some truck shadow showing on *both* sides of the shrinking cyclist.

(b) The audience, in reaction to nearly being run over by the bicyclist, "leaps" off-road to screen-left only to be faced with a snarling dog, so then in reaction to the dog "immediately leaps" back out into the road. This is a 1-2second duration during which the truck has to continue making progress so that...

(c) when the audience "leaps" away from the dog they are back in the street and the truck is nearly on them, blasting the horn and squealing the tires in a panic.

I don't need a shadow with windows showing, but I do need one that grows with the truck, spreads across the back of the bicyclist, and sticks to the tires. This scene is quite good without the shadow, but that shadow makes the difference between people saying "Oh, is that a model truck?" and "Ooo, I saw that truck coming on..."

Does it help to mention that I am using footage of the truck converging on the lens? The jpg above is the beginning of the footage, the ending of which is the starboard-lower quadrant of the truck filling the entire 16:9 frame (audience gets super-closeup of suspension, chassis, radiator, bash bars, and the road back there between tires and body). All during this footage, the tires spin and the truck bounces just like a monster truck does bobbling down the road.

You're going to need more than Vegas to pull this off.
Firstly the shape of the shadow created by the truck depends on the shape of the truck and the position of the light source (the sun).

Then that shadow gets projected onto the various objects in the scene.
Just try this with a toy truck, a lamp and a few objects on a desk, you'll soon see how complex it is. Well don't even need a toy truck, any complex shaped object will do.

Bob.

Bob, you are correct about how shadows cast their own image on objects. Fortunately (no, actually with careful planning) this particular shadow only casts on the ground in this scene. We picked the location carefully for that very concern, and we cut before and after the truck passes the cycist.

I'm not saying this is easy. But if I could get an inverse of the truck image to remain "stuck to the tires" as a child relationship while I'm tracking the truck, then I'm good to go from there.

RCourtney, "EDIT: if you background is more complex, then you will need a 3D app to simulate the subject as Bob stated. You said audience, so the subject may need bumps for bodies"

By audience, I mean the folks sitting in the theater, as if looking through the eyes of a jogger.

Oh, we considered bumps too, and decided the simplest way would be to shoot jogger POV. Heck, we'd even shoot a real truck, but suddenly the local tire-burners don't want to be associated with nearly running over an audience. After a year of hard search, and even with a $2M liability policy, we couldn't find 10ft poles, much less *any* large vehicle to pull off this gag.

Funny, I never figured we'd by stymied by a mere shadow...

OK, that makes it a tad easier but I stll don't think it'd be easy in Vegas.

The truck is a 3D object and Vegas isn't a 3D app. As the truck moves relative to the camera the perspective of the truck needs to change as does its shadow. You can certainly move two 2D objects together in Vegas using 3D planar surfaces and parent / child relationships but I really doubt is this is going to be enough. Also as the truck changes altitiude the size of shadow needs to change. This much you can do in Vegas with a bit of work.

A simple / free 3D app and bit of work would eat this task. All you need do is create a 3D object that's roughly the shape of the truck, put a light source in the correct place, create a ground surface and create a path for the 'truck' and render the thing out. In Bryce you can disable rendering of objects in one render pass and create a mask only render as well. That all comes back into Vegas very nicely.

If 3D apps scare you too much then build a model and shoot that and extract just the shadow. A piece of white artboard, the sun, a suitable solid object, fishing line, a pole. Shoot the shadow on the white board and use a luminance key to extract the shadow. Job done.

Bob.

Have you tried posting this in a Caligari or Bryce forum?

I'd bet you'll find someone who'll put up their hand up to do the truck with spinning wheels and the shadow for peanuts if not for free.

Why not buy a bigger model truck, one of the RC ones with wheels that do spin, again suspend it off wires and shoot the thing with its shadow on white board?

RCourtney, is the truck-shadow.veg V7? I can't open it in V6.

Bob,
"Why not buy a bigger model truck, one of the RC ones with wheels that do spin, again suspend it off wires and shoot the thing with its shadow on white board?"

Well, this is a 1:12 scale RC model which is pretty darned large for models of this work. It was suspended from the rear, wheels are spinning and the entire body is moving relative to the camera in the 15seconds of footage, with the camera focus and zoom altered from full-wide to full-tight in an 6-second Z1U shot transition.

My choice to use universally directed light (equal lighting from all directions) to get a uniformly-clean sharp-edge Chroma-key, it wiped out any hopes of shadows. The screen was 10inches from the truck, the camera just two feet from the truck. In theory, I was not supposed to even be able to get a key anywhere near this good.

But I did lose the shadow.

I like your white board idea, especially if I use a wide-but-focused beam of light to get a sharp-edged shadow. I can always GaussianBlur to the level I need.

Thanks.

Bo, "I've used drop shadows (in track motion) with nice results."
I'm looking now in EventPanCrop, as well as in the help, and see no mention of track motion drop shadows. Boy, I'd *love* to access that feature. How?

Click the "Track motion" button(Located to the left of the "Track FX" button". There you can enable "2d shadow".

I've used it to make a shadow of a chroma keyed person.

Still from the sequence

Bo

OK, here's what I did with Bo's advice (track motion, drop shadow, making some key points to track the shadow with the truck).

BlueTruckWithShadow

This shadow follows the truck, grows with the truck, bobbles with the truck, etc.

I can of course change the shadow density and let the road and painted lines show through. I do have to cookie cutter out the part where the cyclist rides in front...

But this is the shadow effect I was looking for, using only Vegas. Lots of good ideas and warnings/considerations about making shadows for chroma-keyed objects were offered, and I thank all for the effort.

RCourtney,
Thanks, I've now got that up to examine.
Your shadow is from above and behind POV camera, thus the shadow looks like a blur of the front of the truck.
What steps would I take to create a shadow shaped like the side profile of the truck, as if sun were 90deg right of camera?

There is not enough info in the 2D image to make a side view. One could
find software to make a Z axis extrusion, but a truck has a bed. (imagine
glueing the photo of the front on a block of wood and using a band saw to cut out
the shape)

If your chroma key sequence has a side view..... use that for the media file for
track 3 in my example.

If not, you will need to make a mask shaped like the profile of the truck using
a paint program.

Once again you can uncheck/check the Mask Generator on Track 3 to see the
plane. You would need to keyframe as the truck moves.

EDIT: to get the best mask and you have the model place the model truck on
a sheet of plastic or cloth. Position a light source at the correct angle. Using
a magic marker from the underside draw the shadow on the sheet. Remove
the truck and clean up the marker. Take a photo of the sheet.