| Re: Antes de FAC Club [message #53640] |
Fri, 27 April 2007 14:07  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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kuyper@wizard.net writes:
> What precisely do you mean by "put this tower back in the proper
> orientation"? Do you actually want to modify the tower. If so, what
> kinds of modification are permitted, and whjch are prohibited?
> Alternatively, are you trying to find a point of view that makes it
> look "similar" in some sense to the way it would look if it didn't
> list? If so, in what way should the appearance be "similar"?
Here is one approach I have thought about, and haven't tried
to implement yet. If I took contours through the several
cans piled on top of each other, as I got closer to the
top of the tower the contours would get more and more like
ellipses, rather than circles, because the cans at the top
lean more than the cans at the bottom.
If I found the center of each contour, and fitted a line
though them, say with a stiff wire. I would like to be able to
bend the stiff wire into a straight line and tilt the
entire structure until the straight line was perpendicular
to the XY plane and pointing in the +Z direction. As I did
so, I would carry the cans with me.
The effect I am trying to achieve is to stack each can on
top of the other, so that if I look down on them from above
(you can imagine gazing into your lover's eyes), I would
see a sort of bulls-eye pattern.
I'm afraid modesty prohibits me from actually providing a
picture.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Antes de FAC Club [message #53643 is a reply to message #53641] |
Fri, 27 April 2007 12:23  |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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David Fanning wrote:
> Folks,
>
> Here is a question for those of you who haven't started
> your FAC celebrating yet.
>
> Suppose I have a surface that looks sort of like
> cans of various radii stacked on top of one another.
> Big cans on the bottom and progressively smaller
> cans toward the top. But here is the thing, the
> can tower sort of *lists* to one side, as if it were
> thinking about toppling over.
>
> What I would like to do is put this tower back in
> the proper orientation, so that if I looked straight
> down on it from the +Z direction on a line through
> the center of the cans, I would see a sort of bulls-eye
> pattern.
What precisely do you mean by "put this tower back in the proper
orientation"? Do you actually want to modify the tower. If so, what
kinds of modification are permitted, and whjch are prohibited?
Alternatively, are you trying to find a point of view that makes it
look "similar" in some sense to the way it would look if it didn't
list? If so, in what way should the appearance be "similar"?
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| Re: Antes de FAC Club [message #53644 is a reply to message #53643] |
Fri, 27 April 2007 11:34 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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David Fanning <news@dfanning.com> writes:
> David Fanning writes:
>
>> Suppose I have a surface that looks sort of like
>> cans of various radii stacked on top of one another.
>> Big cans on the bottom and progressively smaller
>> cans toward the top. But here is the thing, the
>> can tower sort of *lists* to one side, as if it were
>> thinking about toppling over.
>
> BTW, Coyote thinks this surface looks more like the
> breast of a sleeping woman, but he thinks a LOT of
> things look like that, so I don't know how much credence
> to give it. ...
After reading your first post I was going to say that we needed a
picture to understand it... and now I'm absolutely sure of it!
:-)
--
------------------------------------------------------------ --------------
Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
------------------------------------------------------------ --------------
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| Re: Antes de FAC Club [message #53646 is a reply to message #53644] |
Fri, 27 April 2007 10:50 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
> Suppose I have a surface that looks sort of like
> cans of various radii stacked on top of one another.
> Big cans on the bottom and progressively smaller
> cans toward the top. But here is the thing, the
> can tower sort of *lists* to one side, as if it were
> thinking about toppling over.
BTW, Coyote thinks this surface looks more like the
breast of a sleeping woman, but he thinks a LOT of
things look like that, so I don't know how much credence
to give it. But I have already fitted a plane surface
through the data and subtracted that. That removed
a great deal of tilt, but not all. Subsequent plane
surface fits and subtractions seem to make things worse,
for reasons I don't yet understand.
Thanks,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Antes de FAC Club [message #53788 is a reply to message #53640] |
Fri, 27 April 2007 15:00 |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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David Fanning wrote:
> kuyper@wizard.net writes:
>
>> What precisely do you mean by "put this tower back in the proper
>> orientation"? Do you actually want to modify the tower. If so, what
>> kinds of modification are permitted, and whjch are prohibited?
>> Alternatively, are you trying to find a point of view that makes it
>> look "similar" in some sense to the way it would look if it didn't
>> list? If so, in what way should the appearance be "similar"?
>
> Here is one approach I have thought about, and haven't tried
> to implement yet. If I took contours through the several
> cans piled on top of each other, as I got closer to the
> top of the tower the contours would get more and more like
> ellipses, rather than circles, because the cans at the top
> lean more than the cans at the bottom.
>
> If I found the center of each contour, and fitted a line
> though them, say with a stiff wire. I would like to be able to
> bend the stiff wire into a straight line and tilt the
> entire structure until the straight line was perpendicular
> to the XY plane and pointing in the +Z direction. As I did
> so, I would carry the cans with me.
>
> The effect I am trying to achieve is to stack each can on
> top of the other, so that if I look down on them from above
> (you can imagine gazing into your lover's eyes), I would
> see a sort of bulls-eye pattern.
I sort of get the picture of what you're trying to do, but what I'm
not quite sure I understand is in what sense the transformed surface
should remain similar to the original image. I'm going to describe a
solution. If it's the solution you're looking for, then it's just a
matter of figuring out how to implement it (right now, I have no
idea). If not, at least it will give you an example of the kind of
questions you need to answer before you can solve this problem.
You have surface that looks similar to a series of cans on a bent
wire. Let s be the distance, measured along the wire, from it's
starting point to a particular position along the wire. The wire may
be described by the coordinates [x(s), y(s), z(s)]. Can number 'i' is
centered at a position s[i] along the wire with its axis of rotation
tangent to the wire at that position. It has a length l[i] and a
radius r[i]. I would presume that s[i+1]-s[i] = 0.5*(l[i+1]+l[i]).
I think that what you'd like to do is create a new surface which is
similar to the original, in that it can be described in exactly the
same fashion, using exactly the same values of s[i], l[i], and r[i].
The only difference would be that, for the new surface, xnew(s)=0,
ynew(s)=0, and znew(s)=s. Is that what you're looking for?
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