Re: Rotation of 3D objects

• To: mathgroup at smc.vnet.net
• Subject: [mg86314] Re: Rotation of 3D objects
• From: "Fred Klingener" <gigabitbucket at gmail.com>
• Date: Sat, 8 Mar 2008 05:41:36 -0500 (EST)
• References: <fqo8u2\$t2s\$1@smc.vnet.net>
• Reply-to: "Fred Klingener" <gigabitbucket at gmail.com>

```"Narasimham" <mathma18 at hotmail.com> wrote in message
news:fqo8u2\$t2s\$1 at smc.vnet.net...
> By what command is it possible to create (without writing a code
> separately ):
>
> 1) Reflections of 3D objects about a plane?

surf = ParametricPlot3D[{t, u + t, u*t/5}, {t, 0, 2}, {u, -1, 1}];
Graphics3D[{#, # /.
GraphicsComplex[nodelist_, rest__] ->
GraphicsComplex[ReflectionTransform[{1, 0, 0}, {0, 0, 0}][nodelist],
rest]} &@First[surf]]

> 2) Multiple copies equally spaced  by rotation around an axis through
> two given points?

Same approach (sort of) works:

Manipulate[
Graphics3D[
Table[First[surf] /.
GraphicsComplex[nodelist_, rest__] ->
GraphicsComplex[
RotationTransform[j 2 Pi/n, {0, 0, 1}, {-1, -1, 0}][nodelist],
rest], {j, 0, n - 1}]]
, {n, {1, 2, 3, 4, 5, 6}}]
To understand the method, note the returns from the following:

surf
Graphics3D[First[surf]]
Shallow[First[surf]]

If you want to inspect the many screenloads of GraphicsComplex in its full
glory, look at

First[surf]//InputForm

First[surf] is a GraphicsComplex (which can be rendered with
Graphics3D[First[surf]]). It has a structure that leads with a node List
that can be extracted with a pattern, transformed with the usual tools, then
reassembled into a new GraphicsComplex.

You can inspect the node list alone with

First[surf] /. GraphicsComplex[nodelist_, rest__] -> nodelist

> 3) A single rotation of given object through a given angle on an axis
> through two defined points?

If I understand the question, this is a matter of using your two points to
generate the parameters of your choice for the RotationTransform.

Hth,

Fred Klingener

```

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