May 11, 2012

How do they know the surfer's wave was 78 feet high?

It breaks the 2008 record by 1 foot. 1 foot?! Who does these measurements and how? 
Judges for the awards, considered the official arbiters of big-wave surfing, pored over footage and high-resolution still images from several angles to calculate a more accurate estimate....

They used McNamara’s height in a crouch and the length of his shin bone to help compare it to the wave’s top and bottom....
The measurement is reported in feet, but it's measured in shin bones.

20 comments:

Pogo said...

Well, the knee bone's connected to the shin bone,
Praise the word of the Lord!

Pogo said...

Them dry bones

ndspinelli said...

I've gotten to know some extreme surfers out in San Diego. They travel the world looking for these waves. They are Type TTTTT personalities. They all say the guy driving the jet ski is often even more vulnerable than the surfer. You can't get onto these waves w/o a jet ski.

chickenlittle said...

See, climate change even helps surfers.

edutcher said...

Yes, but how many times was the shin bone broken (if you've ever driven past Sunset Beach on Oahu in January, you know that is no idle question)?

Original Mike said...

"They used McNamara’s height in a crouch and the length of his shin bone to help compare it to the wave’s top and bottom...."

Did they calculate for the projection effect due to the fact his leg was not straight up-and-down?

Robin said...

But was it an imperial shin bone or a metric shin bone?

bagoh20 said...

I would never try that without my water wings fully inflated.

Tibore said...

"They used McNamara’s height in a crouch and the length of his shin bone to help compare it to the wave’s top and bottom....
The measurement is reported in feet, but it's measured in shin bones."


Well... it's not like photogrammetry is not possible - on the contrary, it is very much so - but at the same time, you'd wonder if the margins of errors induced by many of the estimated elements are enough to state with certainty that there was genuinely a foot of difference. I had thought that for real precision, you'd need the distances from the film plane to the object, the exact focal length of the lens, and so on, but I've seen legit photogrammetry done with far fewer - or in some cases, far less accurate - information. So I know that measurements can be bounded (i.e. within a precision of X-inches, or X-feet, or X-centimeters... all dependent on the precision of the known measurements to begin with). But precision to a foot from the distances evident in the article's pictures? Well... maybe it is possible. But I'd dearly like to see those error bars before giving it total credence.

So sure, in the end, they might be in the ballpark. Obviously, they're not a yard off, and obviously, it would be insane to think they've calculated things down to an inch. But evidence is needed to accept that the "foot" measurement is indeed accurate. I'd really like a plus-or-minus in their assertion.

Anyway, my 2 cents. /pedantry

bagoh20 said...

It works pretty well if you are careful. I design and build things all the time by taking photographs of where it will fit and using any known measurement to scale it. In fact, I'm doing one today where I'm designing a hand rail for some steps from a photo. I will design, draw and then build it from 40 miles away and it will fit perfectly when I finally take it there finished. If not, I will blame this blog for distracting me.

CWJ said...

Actually, I would have expected Guinness to use the metric system. Usually when I read about things like this in the American press, we get a ridiculously exact measure in feet, miles, etc that converts nicely into a nice round number of meters, kilometers, etc telling me that they simply converted from the source material for the benefit of American readers.

So 78 feet is a sutprise since it doesn't convert.

KM said...

Shin bones are not the problem here, its where do you consider the trough of the wave to begin the measurement, and when. That can make all the difference and is arguably arbitrary. They should release the photos of the frame grab and calibrated overlay of the measurements to the public.
Otherwise a 1 foot difference makes it seem like its just a great marketing ploy.

bagoh20 said...
This comment has been removed by the author.
bagoh20 said...

Ideally, you lay a photo of one wave over the other, zoom for equal distance from the camera, and match up troughs.

Original Mike said...

"I will design, draw and then build it from 40 miles away"

You must have long arms.

MadisonMan said...

They should include error bounds in the estimate.

Sorun said...

Yabut who measured the shin bone?

Astro said...

Whenever I hear or read the phrase 'shin bone' I am reminded of: Shinbone, the paper edited and published by Dutton Peabody, played by Edmund O'Brien / The Man Who Shot Liberty Valance.
Ok, off topic but so what.

Rusty said...

The length of the board would be a better metric. Having marks on the board a set lengths would be a plus.

Methadras said...

They needed a gauge and some trig. The rest is geometry.