MAP Datum

[kayaker24]

I have noticed that on this page lon./lat. coordinates are displayed using WGS 84 which looks something like:

N 33° 14.153 W 086° 58.044

 

I frequently go to a site (American Whitewater Site www.americanwhitewater.org) where they use coordinates that look like this:

 

Putin Lon: -83.8242035

Putin Lat: 33.8815002

 

Does anyone know what datum this is?

 

Thanks.

[dsandbro]

Looks like decimal degrees. The minus longitude is West.

 

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Friends don't let Friends geocache drunk.

[+The Leprechauns]

Right, the format is decimal degrees. But using which datum? The whitewater site doesn't say (at least I couldn't find an information page upon a quick surf -- no pun intended). But presumably they mean for their approximate put-in and take-out coordinates to be in sync with either or both of the TopoZone topographic maps or the Tiger Census Data Photo Maps that are linked to from the webpage for each whitewater run. TopoZone *generally* uses the NAD27 datum. Tiger uses the NAD83 datum.

 

x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x

If there's no accounting for stupidity, then why do I need to file a tax return?

[kayaker24]

I have found a website (http://members.aol.com/_ht_a/marklent60544/myhomepage/Geocaching/markwellgcfaq.htm#Convert)that tells how to convert coordinates like:

Putin Lon: -83.8242035

Putin Lat: 33.8815002

 

into latitude/longitude.

 

The next question is: Does anyone know how accurate this will be? In case you haven't guessed, its a site that tells us whitwater kayakers where to put in and take out your boat for a particular river. GPS's are an extremely valuable tool in finding these remote locations. I am wondering how accurate these coordinates will be using the conversion method.

 

Thanks

[Lyra]

To convert from one format to another, I use jeeep.com. It seems to be accurate enough, but in order to double check the put-in and take-out points, I like to take a look at the USGS photo on lostoutdoors.com

 

Always wear proper caching safety equipment!

[jfitzpat]

FWIW, using decimal degrees vs. degrees, minutes, decimal minutes is not really a difference in precision, just in base units used.

 

You can confirm this for yourself, use Markwell's method, or the online conversion utility at http://www.jeeep.com

 

Then plug all the formats (ddd.dddd, dd mm.mmm, dd mm ss.sss) into the Map Maker on http://www.lostoutdoors.com and compare the markers placed on the aerial image.

 

-jjf

 

Ooops - I should have refreshed before hitting post - after letting the message sit on my desktop for a bit, I missed Lyra's response!

[+Kaniksu]

quote:

---

Originally posted by kayaker24:

I have found a website that tells how to convert coordinates like:

Putin Lon: -83.8242035

Putin Lat: 33.8815002

 

into latitude/longitude.

---

 

Those coordinates are already latitude/longitude. They are simply in decimal degrees format (DD.DDDDDDD°) rather than the degrees and decimal minutes format (DD° MM.MMM') that you might be more familiar with and that Geocaching.com uses.

 

Since one degree of latitude equals about 69.4 miles, and one degree of longitude equals about 57.6 miles at that latitude, then the precision of those coordinates you give above is at about the level of half an inch -- certainly overkill on the number of significant digits, as no consumer grade GPS is even close to that accurate.

[Kerry.]

As has been mentioned decimal degrees but as with all these types of published marks they generally should be used with caution.

 

As someone mentioned, no mention of a datum, which fails the first co-ordinate rule, in that coordinates without a datum are suspect. Assuming the datum?, well one does that at ones own risk just depending on how critical it might be.

 

Also it is sort of obvious what the format is (in this case) but what if say the Putin lat was 33.5815002 then what, more assumptions.

 

Really I can't see the point why some go to all the trouble of publishing marks yet forget some of the more important issues, like a datum and making the position format "totally" unambiguous and yet go over the top with precision.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go