Re: [Plib-users] CAM using plib was: Wanted--bitmap

[Steve B. <sjb...@ai...>]

Marlin Mixon wrote:

> >So, if this works, you owe me a 2 foot tall foam model of Tux - OK?  :-)
> 
> You got it!

Excellent!
 
> A few additions to the algorithm.  It appears that the MSFS models are
> often non-contiguous meshes--a forward section of the fuselage placed next
> to a rear section.

Bummer.

If there is merely a small gap or overlap then a first pass to 'snap'
together adjacent vertices would be needed.

What you need to do is to delete edges that are NOT shared *before* you
backface cull the model - then after it's back-face culled, delete only
edges that *ARE* shared.  Hence only edges that changed from being shared
to non-shared *because* you backface culled will show up as profile edges.

That's not a bullet-proof strategy...but it'll do.

> So I think the following changes are in order:
> 
> * You have to build a linked list structure of 3-d verticies in order to
>   detect non-contiguousity. (Hey! A brand new word!)
> * Plot a final graph.  Each 2-D vertex needs an attribute telling it
>   which 3-d network it came from.
> * On the final 2-D graph, check each remaining edge too see if it
>   intersects with any other edge.  If so fix the graph so there's a
>   vertex there.

Yes - but they may not intersect.


     ______________________
    |           |          |
    |           |          |
    |___________|_ A       |
    |           | |        |
    |___________|_|B       |
    |______________________|

The edge A/B doesn't intersect anything - but it does need to be discarded.

> * For each vertex, do a point in polygon to see if that point lies in
>   any OTHER polygon and if so delete it.

Point-in-polygon tests can't work in 3D.
 
> I kind of like the hybrid idea.  Any opinions?  Any pitfalls?

I would *strongly* recommend you stay clear of raster-based hacks.

-- 
Steve Baker   HomeEmail: <sjb...@ai...>
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