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Shadow rey trace problem


Shadow rey trace problem

I just had a user ask me about how to project the shadow of a spoon shaped object onto a plane.

There is a point source some distance in front of the spoon. The spoon may not be normal to the point source or to the projection plane.

What I did for him to get a quick answer was to create points on the edge of the spoon, create curves between the point source and the points on the spoon edge. I then use those curves to create in-line points on the projection plane. The more points you create on the spoon edge the better the shadow shape on the projection plane.

Anyone have a better way to do this?

Please, there has got to be a better way!

David Haigh
Phone: 925-424-3931
Fax: 925-423-7496
Lawrence Livermore National Lab
7000 East Ave, L-362
Livermore, CA 94550


Hi David,
This is a classic case for the use of Field points. You place this on your
surface and add a n axis normal to the surface. Make your ray to it then
add the bounce ray. We were showing something very similar when originally
trained on Behavioural Modelling. Was quite a while back but if you search
on these terms especially in PTCU I bet you will find something relevant.

Else point on surface and normal axis in a group and fill pattern sort of

Good luck 🙂


*Brent Drysdale*
*Senior Design Engineer*
Tait Communications

Thanks for all the replies, some techniques I didn't know were there. Problem is none of the address the problem. So here's a picture of what I'm trying to accomplish. This is a physics problem not a light and shadow problem, that was just the easiest way to describe it.

David Haigh

I'm wondering if you could use a VSS with a line as the section and the profile of your 'spoon' as the only trajectory. In the sketch you'd have a single line aligned to the point and the trajectory and long enough to go past the shadow plane. You could then trim the surface back to the shadow plane to get the shadow outline.

I suspect getting the sketch normal right would be the tricky bit. The sketch plane wants to be through the light point at any point along the trajectory I believe. Perhaps a second sketch through the light point on a plane parallel to the shadow plane as the 'normal' trajectory with just a circle? You wouldn't tie the VSS sketch to it; it would only insure that the VSS plane always passes through the light point.

I'm not sure that would do it, but it may spark some thought that'll get you there.

Interesting challenge, I wish I had time to play with it.

Doug Schaefer | Experienced Mechanical Design Engineer
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