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Duf
Mountain climber
Montreal, QC
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Topic Author's Original Post - Sep 1, 2015 - 08:52am PT
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Somehow, the bookshelves of my local climbing store still carried the 1st edition of High Sierra Climbing.
As part of planning my trip, I'd like to enter the main GPS waypoints in my GPS.
The GPS coordinates for the start of Mt Whitney Trail (page 38) are as follows: 36° 35' 223" 118° 14' 409"
This format doesn't make much sense, as there can there can be only 60" in a minute - so the maximum number of seconds is 59"
Question 1: do you know how I should interpret these coordinates?
36° 35' 22.3" 118° 14' 40.9"
OR 36° 35.223' 118° 14.409'
Question 2: do you know which "datum" these coordinates refer to?
WGS84, NAD83, ???
I have read the discussions around which format should be adopted for all current & future SuperTopo guidebooks. My questions is specific to High Sierras 1st edition.
Thanks!
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kunlun_shan
Mountain climber
SF, CA
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This format doesn't make much sense, as there can there can be only 60" in a minute I have the 1st edition of High Sierra Climbing also. I haven't used the GPS coords in it, and yes you are correct that they show degrees minutes seconds….. with seconds greater than 60.
I think its probably a consistent typo throughout the book and the numbers are really degrees decimal minutes.
Comparing the coordinates from:
http://www.summitpost.org/east-face-east-buttress-east-ridge-of-russell-trip-report/169096
Russell W Summit 36 35.403, 118 17.447
Russell E Summit 36 35.435, 118 17.355
HSC, page 58 shows
Russell W Summit 36 35' 403", 118 17' 447"
Russell E Summit 36 35' 435", 118 17' 355"
I bet if you search and compare other coordinates, it will verify this.
The book does not say which datum was used. Its probably NAD83. I would email Chris McNamara and ask.
Or try figure it out comparing with GPS data that does specify which datum is used.
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Duf
Mountain climber
Montreal, QC
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Topic Author's Reply - Sep 1, 2015 - 03:34pm PT
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Thanks kunlun_shan!
I agree that the coordinates must be interpreted as degrees decimal minutes, in other words 36°35.223'N 118°14.409'W
If I assume the datum is NAD83 and compare the coordinates in the guidebook to those in the National Geodesic Survey, I get a 14m acuracy on latitude (good enough for me) and 47m accuracy on longitude (seems a bit high).
I guess I'll try to get the 2nd edition of the guidebook and use its coordinates - and hopefully it will clarify the "datum" question.
Thanks again.
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CCT
Trad climber
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The datum really doesn't matter for the level of accuracy that you need. The routes are all pretty obvious once you are close to them. Until then, just point yourself at the large obvious mountain, and follow whatever trail is under your feet. Cairns, packed dirt, and the topo are far more useful than exact coordinates.
If you must have a datum, I'd guess WGS84 or NAD83. State plane is the better choice for accuracy, but is not generally used outside of commercial or academic applications.
Honestly, I'd be surprised if your hiking GPS unit is capable of consistently delivering sub-10M accuracy anyway.
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ruppell
climber
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Honestly, I'd be surprised if your hiking GPS unit is capable of consistently delivering sub-10M accuracy anyway.
What? My phone gets 3M accuracy all the time. I'd find it hard to believe a dedicated GPS unit wouldn't.
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CCT
Trad climber
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Try it.
Go to a point. Write down the coordinates shown on your phone. Leave, and come back the next day. Return to the same coordinates. Notice how far away you are from your previous spot.
Now try this again under trees, in a canyon, or in a dense urban environment.
Now try it in an area without cell reception, or with poor cell reception.
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ruppell
climber
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I have. I'm talking about in the Sierra's with the phone in airplane mode. So no cell triangulation. Strictly the GPS chip on the phone. It's always within a 3M range. Set waypoints always return me to exactly where they where set. I use Backcountry Nav Pro for the navigation on a lot of stuff I do. Brought it a two years ago and haven't purchased a physical map since.
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Ed Hartouni
Trad climber
Livermore, CA
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if you interpret this as: 36° 35' 22.3" 118° 14' 40.9" you get the decimal coordinates: 36.58395278°N, 118.2344694°W
when you put this into Google Earth you are off by quite a bit...
interpreting this as: 36° 35.223' 118° 14.409' you get the decimal: 36.58705°N, 118.24015°W
which is very close to the start of the trail...
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Duf
Mountain climber
Montreal, QC
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Topic Author's Reply - Sep 3, 2015 - 01:09pm PT
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Thanks everyone for your input. I'll let you compare the accuracy of your devices ;)
@Ruppel, thanks for the name of your GPS app, I'll look it up!
@Ed, agreed.
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