Thibaut Jonckheere wrote:


> translate/rotate the car object as needed in pov. I wish a had the 
> spline describing the car path along the whole knot, so I could for 
> example make an animation, but this would require to read manually the 
> position of a few hundreds vertices in wings :-/ I could not figure an 
> easy/lazy way to get this info yet...
> 
Not sure if it is easy/lazy enough but I sometimes make use of the 
ability in Wings to assign materials.  When selected polys are then 
exported into .obj format, the material assignment can be used as a sort 
of label to identify vertices in the .obj file.  I then parse the file 
with an external script ( I like Python ) which puts the vertex/normal 
info into sdl format, arrays for example.

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Bill Pragnell wrote:
> This is really nice. Took me a couple of seconds to 'see' what I was looking
> at! 

This couple of seconds interests me ! Can you say if it is because of a 
"technical"problem (image too dark, not enough contrast,...), or because 
it is due to the complexity of the object shown ? I guess many people 
(including me) won't often make the effort, in usual life, to look 
longer at a picture which seems unclear or confuse at  first sight.

I sympathise with the background problem - I too had trouble thinking of
> anything simple and effective. I'm now spending longer on the background
> than I am on the knots...
> 
> Suggestion, to be used/recoiled from as you see fit: Put a layer of cloud
> beneath the knot, then a moonlit landscape (fields, etc) below that. The
> effect would then be of the knot floating 1000s of ft in the air, with the
> viewpoint even higher but looking straight down.

Thanks, I will try something in this vein for the background. I am quite 
conviced now that what is lacking is a feeling of depth behind the knot.


> 
>>The cars are simply placed in pov, using position and angle infos read
>>in Wings3D. I just chose the points where I wanted the cars to be, read
>>the corresponding position (and angles) in Wings, and then
>>translate/rotate the car object as needed in pov.
> 
> Another option would be to use trace().

In fact, I use both: I perform a trace to get the angle between the 
local normal and the vertical (y axis), and the wings info to get the 
rotation angle in the horizontal plane.


> I specifically looked for parametric functions describing knots so I could
> generate them algorithmically. If there's some way of persuading knotplot
> to give up a mathematical function, it'd be no problem. It might be worth
> contacting the author in this regard...

I may have a look at the math formulae behind this knot. But it is too 
late for my image now: my knot does not follow exactly the one given by 
knotplot.

> It'd be great to see some more of this work - keep it up!
> Bill
>

Thanks for the support !


Thibaut

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Jim Charter wrote:
> Thibaut Jonckheere wrote:
> 
> 
>> translate/rotate the car object as needed in pov. I wish a had the 
>> spline describing the car path along the whole knot, so I could for 
>> example make an animation, but this would require to read manually the 
>> position of a few hundreds vertices in wings :-/ I could not figure an 
>> easy/lazy way to get this info yet...
>>
> Not sure if it is easy/lazy enough but I sometimes make use of the 
> ability in Wings to assign materials.  When selected polys are then 
> exported into .obj format, the material assignment can be used as a sort 
> of label to identify vertices in the .obj file.  I then parse the file 
> with an external script ( I like Python ) which puts the vertex/normal 
> info into sdl format, arrays for example.


Hum, parsing the .obj export sounds interesting, even if it not totally 
lazy :-)  The car trajectory is a single edge loop in my Wings object, 
so I guess I can bevel it, assign a material to the faces, and export.

Thanks for the tip !


Thibaut

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Thibaut Jonckheere wrote:
> it is due to the complexity of the object shown ? 

In my case, a lack of clues about the scale. It wasn't obvious 
immediately that the little dots of lights were automobiles.

Personally, I like that little delay. It's what art is about.

-- 
   Darren New / San Diego, CA, USA (PST)
     "I think these anchovies are spoiled.
      They're not flat."

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Thibaut Jonckheere <tua### [at] yahoofr> wrote:
>I wish a had the
> spline describing the car path along the whole knot, so I could for
> example make an animation, but this would require to read manually the
> position of a few hundreds vertices in wings :-/ I could not figure an
> easy/lazy way to get this info yet...
>
>
>
> Thibaut

You might check out my knotsplines macro, where I describe how to get a
spline from the povray-exported bicubic patch done by KnotPlot.

Basically, I use Microsoft Word (Python or something similar would be much
easier, I'm guessing), to take the first vertex point from each patch (I
know, it would be more accurate to take one of the interior ones, since the
"edge" vertices are control points....), and put them into an array, and
form the spline from the array -- the readme/macro shows how:

http://tinyurl.com/lfvar

(although, when I try to save the zip file over the web view, it comes
through corrupted; when I try to download it with the newsreader it works
fine.  I'm not sure why.)

If you'd like a copy, I can send you one.

Dave Matthews

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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> If there's some way of persuading knotplot
> to give up a mathematical function, it'd be no problem. It might be worth
> contacting the author in this regard...
>

I don't think that KnotPlot ever figures an explicit parametric
representation.  I think it works from points (the "beads") and splines.
That's a frustration for those of us more used to calculus and closed-form
solutions; but, I think, once one gets used to approximating from spline
points, the calculations can be much quicker and simpler (I'm still working
out a few of these, when I get the time, which is scarce right now....)
Also, I'd imagine that the parametric equations for some of the more
complicated knots would be hideous.

Dave Matthews

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Thibaut Jonckheere wrote:
> Jim Charter wrote:
> 
>> Thibaut Jonckheere wrote:

> Thanks for the tip !
> 
Welcome.  Another thing I do, btw, combines Bill's suggestion of using 
trace() with the Wings' ability to export selected polys.  That is, I 
use the information captured from the .obj file to define a spline which 
rides above the mesh surface along a path I want.  I then use the spline 
as a set of "launching" points for the trace() function.  That way you 
only have to manually capture (export) a relatively small number of 
polys to determine the path for a spline, then walk the spline and use 
trace() to get as many surface points as necessary for a smooth animation.

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Thibaut Jonckheere <tua### [at] yahoofr> wrote:
> This couple of seconds interests me ! Can you say if it is because of a
> "technical"problem (image too dark, not enough contrast,...), or because
> it is due to the complexity of the object shown ?
Nothing so ominous - just a mental stumble on my part; I simply wasn't
expecting it. I could see the knot form quite clearly from the thumbnail,
and mentally filed it as a belt or ribbon before I'd opened the full
version. Then I noticed the headlights... :)

It worked a bit like a joke punchline.

Bill

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> You might check out my knotsplines macro, where I describe how to get a
> spline from the povray-exported bicubic patch done by KnotPlot.


In fact, I took a look at your macro before starting my image. It looks 
really powerfull. But I decided to go this time with a non-mathematical 
way of doing the thing: I just saw a relatively simple way (although a 
bit tedious) to get what I wanted with Wings, the only guide being the eye.

Thibaut

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Jim Charter <jrc### [at] msncom> wrote:
> Welcome.  Another thing I do, btw, combines Bill's suggestion of using
> trace() with the Wings' ability to export selected polys.  That is, I
> use the information captured from the .obj file to define a spline which
> rides above the mesh surface along a path I want.  I then use the spline
> as a set of "launching" points for the trace() function.  That way you
> only have to manually capture (export) a relatively small number of
> polys to determine the path for a spline, then walk the spline and use
> trace() to get as many surface points as necessary for a smooth animation.

Jim, that's brilliant!

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