I’m just working my way through the StandingModel.any and I’ve come across
RotMat. I’m
quite happy with the 2 argument version but I’m not really sure what the 3
argument one
is doing.

The manual says:

RotMat3Points Rotational tranformation matrix for a coordinate system defined by
three
points.
The first point is the origin of the system; the second gives the direction of
the first (x)
axis.
Together all three points must span a plane which will be the plane of the first
(x) and the
second (y) axes, having the third (z) axis as normal.

But that doesn’t actualy leave me much the wiser. What further confuses me is
that the
matrix produced by this often seems to get its columns swapped around before
being
used.

It’s probably elementary geometry that I ought to know so could someone point me
at
some suitable reading material?

I have uploaded a small powerpoint figure to the filesection of this
group, the file is named “RotMatThreePoints.ppt”, i hope it will
make it more clear.

The first point defines the origin of the coordinate system, the
second point gives the direction of the x axis. The third point will
together with the p1 and p2 define the xy plane. So p3 will always
be in this plane.

I am unsure about which place in the model you are referring to when
you say that the coloumns are being swapped before being used?.
The sign “’” may be used depending on what kind of coordinate
transformation is needed. In the file section of the group there is
a small example of coordinate transformations, please
see “smallexamples/coordinatetransformations.any”

Please do not hesitate to ask again if you have further questions.

Best regards
SÃ¸ren, AnyBody Support

— In anyscript@yahoogroups.com, “wisellers” <wis@…> wrote:
>
> Hi All,
>
> I’m just working my way through the StandingModel.any and I’ve
come across RotMat. I’m
> quite happy with the 2 argument version but I’m not really sure
what the 3 argument one
> is doing.
>
> The manual says:
>
> RotMat3Points Rotational tranformation matrix for a coordinate
system defined by three
> points.
> The first point is the origin of the system; the second gives the
direction of the first (x)
> axis.
> Together all three points must span a plane which will be the
plane of the first (x) and the
> second (y) axes, having the third (z) axis as normal.
>
> But that doesn’t actualy leave me much the wiser. What further
confuses me is that the
> matrix produced by this often seems to get its columns swapped
around before being
> used.
>
> It’s probably elementary geometry that I ought to know so could
someone point me at
> some suitable reading material?
>
> Thanks
> Bill Sellers
>