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From: Bill (no email)
Date: Fri Jan 20 2006 - 04:01:25 EST
> Yup.
>
> Good catch Bill!
As the old saying goes, pick off the easy meat, then work on points for
style. It was bogus, IMHO, from the git go.
"He knew the focal length of the lens, the size of the sensor in the camera
and the number of pixels across the image."
One point at a time:
"He knew the focal length of the lens"
Which matters, why? Perspective is a matter of distance, not focal length.
An experiment--Take a camera, use the longest (focal length) lens you have
or highest zoom setting, and move back to include your house, mailbox, and
other landmarks in the frame. Now (without moving) use the widest-angle
lens or lowest zoom setting you have. Enlarge the portion of the wide-angle
shot matching the telephoto image to the same size as the telephoto shot.
The perspective will be exactly the same. Ditto for the horizon and object
at an "infinite" distance from the same location.
"...the size of the sensor in the camera..."
Again, so what? Size of the sensor vs. focal length/angle of view
determines magnification, not perspective. The sensor is just a matrix/grid
that determines resolution. Without going into depth about coverage, focal
length and view angles, yadda yadda yadda; if the resolution is sufficient
to provide enough pixels in the "grid" for accurate measurement, it's a done
deal.
"...and the number of pixels across the image." As you know by now, I do
not hate repeating myself. So what? All the author proposes is using the
sensor grid that transforms photons into 24 bit deep (or more) pixels as a
measuring device. (Sorry about too much information, but for this
explanation, bit depth does not matter much. 16+ million colors or 256
colors matter only if it would help the eye/software in resolving a color
image. Sun and horizon, relatively high-contrast boundaries.
In the end all the matters is that the sensor created a grid that we can
calibrate/measure against known values (in this case, sun SD vs. elevation).
Is this idea new to the list? Nope. Frank suggested it in his digital
photos of Chicago from the shores of Indiana. The only question might be
lens/sensor distortions of the image.
That being said, I chose the obvious to pick on first.
To Frank Swift:
Unless this was a not-so-clever hoax on your part, I don't support shooting
the messenger (it keeps me alive;-), and apologize if you are accurately
recounting a published article. Perhaps GPS is forbidden in the race and
some sort of "GPS watch" was used as the $30 radio-signal-controlled
timepiece doesn't work in those waters?
It just struck my funny bone. Digital camera, computer with a cel nav
program (Davis?), $$ professional image-editing software (PhotoShop),
Nautical Almanac data, (and in my mind's eye--pods on the mast etc. relaying
data from 1 of the big 2, or 3, racing-software programs working with the
boats polar diagrams.) The only thing missing was a radar gun. <G>
Bill
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