Extruding the Outline of a Shadow.

There has to be an easy way to do this but I’ll be darned if I can figure it out. Searching has gotten me a few close hits - but no cigar.

I need to project the shadow (sharp edged) of an object (say, a 3d blob) onto a planar surface and then linearly extrude that outline to become another 3d object. I can’t use a cut section because of the irregular shape of the object.

What I’m I missing?

What I’m I missing?
We’re missing a clear description of what you want to do.
I see no screenshots, annotated images, your blend current blend file !

Sorry. Here’s a pic (not to scale). Lamp (at infinite distance) casts a shadow (black curve) of an irregular object onto a plane. I need to extrude that outline along the normal to the plane. In other words, I need a projection of the shape onto the plane which will then be extruded along the plane’s normal.

Probably more steps than you want but:

take a photo from ortho view (best if dark object on light background)
open it in a vector program such as Illustrator or Inkscape (free like Blender)
trace it (using auto-trace feature) to produce a curve and save as SVG file
import SVG curve back into Blender (and correct the size)
make curve into mesh (alt C)
edit mode, give mesh a face
extrude mesh

I did this in about 2 minutes, but I’m used to working curves in Illustrator and importing them as SVG files into Blender. It might cost you some time learning those steps.