Re: [PSUBS-MAILIST] Reverse engineering in CAD

[Ian Roxborough <irox@ix.netcom.com>]

Hi Peter,

I don't really know anything about autocad2004, but if it's worth it's
salt then it I'll probably have the following features.

NURBS!

See if your cad/modeling software has Nurbs support (Nurbs are just
fancy curves or a fancy word for curves).  You should be able to use
the Nurbs tool to create some boat like curves, similar to the ribs
of a woodern boat (you may want search drawning Nurbs or curves on
the internet or in the library, but if mess around long enough you'll
probably get the hang of it).

Once you have enough curves (draw them a foot a part, or whatever you
think it takes) to get it to start looking boat-ish, then save your
work and look for a "skinning" tool.  A "skinning" tool (I've no idea
what it will be called in autocad) should allow you to select all your
curves, then create a skin that fits prefectly over the curves.  You'll
probably find that you have to edit the curves a few times before it
starts looking correct.

But that's pretty much it.  Not too different from the join the dots,
only with curves.... ;-)

If your doing solid modelling, then hopefully there is tool for giving
the skin 'thickness' or volume.  Otherwise you might have to create a
copy of the hull and shrink it down by a very very small amount and put
it inside the bigger hull skin, then joint the two object together. The
distance between the inner and outer skin determines how thick the hull
will be.

This is how I would tackle the problem, but it's probably worth noting
that the software I use to do this type of thing isn't a true solid
modeller.

Hope this helps.

Ian.



On Fri, 18 Jun 2004 08:36:12 +1000 (GMT+10:00)
Peter McKellar <submckellar@earthlink.net> wrote:

> Hi All,
> 
> I am trying to reverse engineer a boat hull for my pressure hull's exo-skeleton.
> 
> I am using autocad 2004 and solid modelling, but i just can't split the shape into the primitives i need to draw it (in my head anyway).  I am also trying to scale it down (and this has its own pitfalls as it may not scale and retain its properties).
> 
> I have a jpg of it, including cross sections both horizontally and vertically at a number of points.  I am considering pasting these planar jpgs into the drawing and then doing a 3d join-the-dots.
> 
> can anyone think of a better solution?
> 
> cheers
> peter
> 
> 
> 
> 
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