From: Bob Goethe
Sent: November 12, 2017 5:48 PM
To: 'Carly and Bill'
Subject: NASA: Height of Boardwalk/Platform at Sunset Point
If you can regularly access a nice platform for taking sights from, that will be great! Personal comfort will actually contribute to better sights....plus there is everything to be said for an esthetically pleasing place to watch the sea.
Now, knowing the height of your eye (not the height of your feet, but your eye) above sea level is quite important. The higher you are above the sea, the more little inaccuracies in your estimate of height will get smoothed out. If you look at the dip table on the right side of the page that is just one page from the front of the Nautical Almanac, you can see that when you are close to the water’s surface, 0.2 meters matters. Once you get 20 meters or more above water level, those 0.2 m increments become 2.0 m increments.
I just tested the GPS receiver in my phone to see if it could determine altitude differences. It totally fails. It read my altitude as 664.5 meters when I am on the top floor of our house. I went down a level, and my reported altitude became 370.0 meters. That is, I went DOWN 2 meters in my split level house, and my phone reported that I went UP by 5.5 meters.
I have read that GPS does pretty well with horizontal location...and less well with heights. That does indeed appear to be so. Maybe GPS will eventually become accurate as pertains to vertical differences...but that day is not today.
For now, do the best you can at estimating the height of your eye above the sea when standing on the platform.
Later on, once you start to get good at sextant use, we will hope to see that your positions start to show a good, tight cluster that are all – on average – 4 miles (or whatever) away from your actual position. Once we get that cluster, we will be able to infer how high up you are, and create our own dip calculation that may well be quite accurate for when you are standing on that platform.
Now, as long as that platform works for you, great. If the rich-and-famous start giving you grief over using their boardwalk, then do keep in mind that in Canada, private individuals can only own land above the highest, high-water mark. Everything below the highest, high-water mark is public land.
So no matter who owns what, you are always legally entitled to walk along the beach or the rocks below that point where the last storm threw up logs and driftwood.
If you can’t use the platform, you can always walk along the beach/shoreline to any spot you like. From there, of course, you can stand where the soles of your shoes are just before getting wetted by incoming waves, and then figure your height-of-eye at 1.7 meters, or whatever.
If you CAN regularly use the boardwalk/platform, then I will get you organized to be able to know the height of the tide at any given time, and we can dial in your height of eye.
"As I sail, I praise God, and care
Luke Foxe, Arctic Explorer, 1634
I desire no more delight
Than to be under sail and gone tonight.
Gratiano, in Act 2, Scene 6, The Merchant of Venice
By William Shakespeare, 1596
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