Slicing a potato

Hi,
I've got a potato-like 3D shape that was reconstructed from some
anatomical images. I need to cut it into slices (ultimately so that I
can assign different properties to different slices). What makes sense
to me is to create a series of thin hexahedra (such that every other
slice is represented), and intersect this with the potato to obtain
half the slices. Then subtract those slices from the potato to get the
other half. Does that sound like a reasonable way to do it?

Assuming an affirmative answer to that question, would someone be able
to quickly rattle off the command to create a solid hexahedron from
eight coordinates?

Thanks,
Adam

 

What's a "3d shape"? A solid? A mesh? A surface?

 

A solid.

Actually it starts as a bunch of triangles, and I convert it to a
solid, so if a mesh or surface will make it easier, it can be that as
well.

Adam

 

Why not make a few copies in place, use another solid, carefully placed, and
then subtract, and repeat?

 

How about just using the "Slice" command? Orient the UCS to the plane you
would like to slice, draw a circle at each elevation you need a slice, then
slice away.

Slice >> Object (select a circle) >> Both (to retain both halves)

--
Patrick Hughes

Engineered Design Solutions
http://www.engds.com

Chronos: Time Logging for AutoCAD
visit http://www.engds.com/Products/Chronos/Chronos.html

 

Can you tell I don't do a lot of 3D solid work? ; )

 

Thanks! Even easier than I had expected.

Adam

 

Heh Heh

--
Patrick Hughes

Engineered Design Solutions
http://www.engds.com

Chronos: Time Logging for AutoCAD
visit http://www.engds.com/Products/Chronos/Chronos.html

 

You're welcome

--
Patrick Hughes

Engineered Design Solutions
http://www.engds.com

Chronos: Time Logging for AutoCAD
visit http://www.engds.com/Products/Chronos/Chronos.html

 

I perhaps spoke too soon. I am not familiar with all that AutoCAD is
doing with the SLICE command. I have 100 planes defined in the same
coordinate system as my potato. My first effort was to make a lot of
slice commands using those same coordinates, e.g.,

slice
all

3points
-20,121.103,294.725
-20,61.8016,303.852
20,61.8016,303.852
Both
slice
all

3points
-20,120.746,292.407
-20,61.446,301.542
20,61.446,301.542
Both
slice
all

3points
-20,120.387,290.072
-20,61.0879,299.219
20,61.0879,299.219
Both

But this doesn't seem to produce the desired result. The first several
are correct, and then it falls apart. From documentation I guessed
that AutoCAD is changing the UCS on me. So I inserted a "ucs world"
before each "slice" commmand. This doesn't solve all the problems
either.

(I've plotted the planes in Matlab, by the way, so they're in the
right place.)

Any help appreciated,
Adam

 

If you have Dynamics UCS's turned on (the DYN button), AutoCAD will try
to set itself to the UCS of whatever surface the cursor is over. Maybe
you need to be sure DYN is turned off... just a thought.

-Bill

==========

 

Thanks, I will try that. I work at a computer in the library (I am a
grad student), so it would be helpful to have a number of options to
try. Are there any other things that might be messing with the UCS?

(And just to confirm, am I correct in thinking that the SLICE command
accepts coordinates in UCS?)

Thanks,
Adam

 

Are all the slices parallel with each other?

 

Slice accepts coordinates in the current UCS, whatever that happens to
be. Pay attention to the prompts: if you are feeding three points to the
routine, be sure to specify the "3point" option in your (command)
statement. Otherwise, the last point might be getting interpreted as a
the reply to the "Select side to keep" prompt.

Note that AutoCAD 2008 (and maybe 2007? I forget) defaults to a
two-point vertical slice in the current UCS unless you specify the
"3point" option.

Good hunting!

-Bill

=========

 

Some of them are close, but I doubt any of them are actually parallel.
They're normals of an L-shaped spline (a curved L). None of them
intersect within the volume.

Adam