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Author Topic: Datum settings  (Read 4592 times)

nowacc

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Datum settings
« on: January 12, 2013, 08:46:15 AM »
I have a question on map datum settings. I have a older Garmin Map 76 that I have many saved waypoints from which I saved at the point itself. Not projecting it anyway from any mapping program. I was at the spot and saved a waypoint. I found out the datum setting was NAD 27 central.
 I got a new Garmin Map 62 which I'm transfering the way points to and found I should be using WGS84.
My question is the map datum setting is only used for placing the waypoint on a map in the correct location. The Lat-Long saved on the GPS is the same and would take you back to the exact spot of the original way point minus the 5'-12' variation.
I use Garmin Mapsource/Basecamp with topo maps/ fishing hot spot lake maps to see where I was.
I wanted to use Mapsource to export my waypoints from the old GPS and import them onto the new GPS. Does the Datum setting matter for this use?

leszekp

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Re: Datum settings
« Reply #1 on: January 13, 2013, 05:57:43 PM »
Doesn't matter, The native coordinate system for GPS is latitude/longitude, WGS84; if you save a location, your Garmin (old and new) will save it internally in that format. When you set a different datum on your Garmin, your GPS will convert from WGS84 and display the coordinates in the new datum, but the internal reference coordinates stay as lat/long, WGS84.

If you downloaded the waypoints from your old GPS with any program, they would have downloaded in lat/long, WGS84; no need to worry about datum shifts. If you have written down the coordinates in NAD27, then you would either have to convert them to WGS84, or enter them in your GPS with the datum set to NAD27; in the latter case, your GPS would convert them to WGS84 and save them in that datum.