Le 06/06/2017 à 19:01, Bald Eagle a écrit :
> Le_Forgeron <jgr### [at] freefr> wrote:
> 
>> That's it for normal gear.
> 
> Indeed.   I learned a LOT when I started looking into modeling involute spur
> gears.
> 

That's the only reasonable gear !
(but most people draw the involute too far inside. inside the base
circle, it cannot be involute, and yet it need some clearance down to
dedendum circle.
And some of them think the distance between the base circle and the
pitch circle is proportional to them: IT IS NOT. It is part of the
teeth, and that's is fully set by the addendum, which must be identical
on each element of a pair)


> 
>> Now, could you explain what you intended to do with povray and gear ?
> 
> Well, the basic idea was to see if, using a simple photograph or scan of an
> existing gear, if the number of teeth could be determined automatically and
> accurately.  Just like in the link.
> 
> There seems to be a fair amount of image processing algorithms employed, all of
> which use a 2D Fourier transform and its inverse to do things like hole-filling,
> edge-detection, etc.
> 
> It would also be an interesting extension of the idea, if, once the basic
> parameters of the gear were established, a 3D model could be generated.
> 
> Then you could automatically generate a parameter file, an include, or a mesh
> from existing gears.

The real (interesting) problem for povray is the computation of the
involute, as a native shape... then maybe some native gear shape, to
handle more natively than a complex union/intersection, per tooth ?
(nah, I would reuse my interunion object for that, probably...)
(or may be a "duplicate teeth" object, where all intersections get
rotated to a single teeth)

mmmhhh, interesting...

> 
> But the main idea was to be able to count the teeth.
> Especially when there are a LOT of teeth, and the gears look very similar.
> http://images.esellerpro.com/2131/I/680/19/RU5-0175.jpg
> http://images.esellerpro.com/2131/I/680/17/RU5-0174%20003.jpg
> 

helical gear... yet another beast... yummy (and more silent than the
basic gears at a small cost of maximal power)

The real hungry would go for hypoid gears, they are really painful.

> 
> I thought perhaps I could start with some basic image clean-up, then try to
> figure out the center point, and then the radii of the addendum and base circle
> so that I could determine the pitch circle and maybe the dedendum.
> 

If you have physical access to the gear, the fastest is to use a tailor
rule (the soft thing the tailor uses to measure) around the full circle,
and measure a small number of teeth. You might be off by a few unit, but
it's fast. (but does not work for gear with teeth on the inside,
including epicyclic gears)

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