[ODE] Joint Naming

[Adam Moravanszky [Novodex]]

Hi,

while working on improving joint support for an app that will support both
ODE and Nx physics back ends, it occurred to me that there is a good
opportunity for misunderstandings regarding joint naming.

In particular, I think the picture for slider joint in the ODE user's guide
is misleading.  The joint has a circular shaft, which makes one think that
rotation around the shaft may be possible.  However, when one considers that
such a joint would need an additional anchor parameter, it becomes clear
that rotation around the axis is in fact not possible.  It says this too in
section 3.5, though not later in the section on slider: "... a slider joint
that constraints the ``piston'' and ``socket'' to line up, and additionally
constraints the two bodies to have the same orientation."

We call such a joint a Prismatic joint, and draw it in the manual with a
square shaft.  We also have joints called sliders, with circular shafts,
which is what can be created in ODE by combining a slider and a hinge
through a proxy body.

Obviously it is inconvenient to do any sort of renaming, but I would suggest
changing the picture in ODE.

--Adam

--  Adam Moravanszky
/*================*\
|Chief Software Architect
|NovodeX AG
|physics middleware
|www.novodex.com
\*================*/