Jon Frommelt
I think I can contribute to this geeky discussion a bit. . .
First, let me say that the unidentified rider was, in fact, me. Apologies
to the officiating staff for making the puzzle more complicated than it
needed to be.
One minor clarification to Mike's description: the bottom of the wheel is
actually NOT moving relative to the ground--it is going exactly zero miles
per hour (provided your not locking up the brakes or spinning out). The hub
is moving at the speed of the bike, and the top of the wheel is moving twice
the speed of the bike.
As to the details of how the image is created, you can see the vertical
images that the camera captures by zooming in on the photograph. You will
see that the spokes are individual straight sections that, when combined and
viewed as a composite, appear curved.
As the front of the wheel entered the frame, a thin vertical slice of the
image was taken. At the next moment in time, another slice was captured,
but the wheel had rotated slightly. Repeat, and you get the al dente spokes
in the final image.
Since the spokes on the top of the wheel are moving increasingly rapidly the
farther they are away from the ground when the pass the finish line, they
are captured in fewer "slices" of time and therefore are less distorted.
Jon Frommelt
-----Original Message-----
From: obra-bounces@list.obra.org [mailto:obra-bounces@list.obra.org] On
Behalf Of Mike Murray
Sent: Tuesday, October 31, 2006 6:05 PM
To: 'Joel Morrissette'
Cc: obra@list.obra.org
Subject: Re: [OBRA Chat] Mast B Bicycle Attorney rider
http://www.finishlynx.com/
Mike
-----Original Message-----
From: Joel Morrissette [mailto:news4joel@gmail.com]
Sent: Monday, October 30, 2006 19:20 PM
To: mike.murray@obra.org
Cc: obra@list.obra.org
Subject: Re: [OBRA Chat] Mast B Bicycle Attorney rider
Inquiring geeks want to know - could you post a link to more info
about how the system works? I recall you did in the past, but I can't find
the email.
Thanks,
Joel
On 10/30/06, Mike Murray wrote:
Actually the image is considerably more narrow than 1 cm.
The width of the
subject in each frame depends on the lens and the distance
from the camera.
The system scans up to 2000 lines each second. These
vertical lines are
then assembled into a picture. This picture is not really a
picture of
anything that really existed but is actually a graph with
the horizontal
representing time and the vertical being what was on the
line at that time.
Things that are moving fast appear more narrow and things
that move slow are
wider. Since the spokes at the top of the wheel are going
twice as fast as
the ones at the bottom relative to a stationary observer
they get squeezed
together at the top and stretched apart at the bottom. This
causes them to
look bent. Trispokes look even sillier.
Mike Murray
-----Original Message-----
From: obra-bounces@list.obra.org
[mailto:obra-bounces@list.obra.org] On
Behalf Of Jesse J. Finch Gnehm
Sent: Monday, October 30, 2006 15:28 PM
To: obra@list.obra.org
Subject: Re: [OBRA Chat] Mast B Bicycle Attorney rider
I believe they look that way because the finish line camera
only records
a 1cm picture and the image is the composite of the person
crossing the
line. As a result, the spokes change position in each part
(frame) of
the image as the rider rolls across the line.
Eric Kytola wrote:
> what kind of spokes are those.....al dente?
>
> -----Original Message-----
> From: obra-bounces@list.obra.org
[mailto:obra-bounces@list.obra.org]
> On Behalf Of Candi Murray
> Sent: Monday, October 30, 2006 1:55 PM
> To: obra@list.obra.org
> Subject: [OBRA Chat] Mast B Bicycle Attorney rider
>
> Anyone know who this is?
>
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--
Jesse J. Finch Gnehm '99
Director of Parent Giving
Willamette University
503-375-5319
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