Datums and waypoints

[jb12string]

I was wondering how changing Map Datums and coordinate formats affects stored waypoints? I typically use UTM when I am using my GPSr with a paper topo map and I think the ones I use most often are NAD27. If I mark a waypoint when I am in UTM and NAD27, what would happen if I tried to go back to that point while I was in NAD83 and Lat./Lon

[+Tui Chub]

I was wondering how changing Map Datums and coordinate formats affects stored waypoints? I typically use UTM when I am using my GPSr with a paper topo map and I think the ones I use most often are NAD27. If I mark a waypoint when I am in UTM and NAD27, what would happen if I tried to go back to that point while I was in NAD83 and Lat./Lon

 

The gps should do an internal conversion between the Datums and projections.

[+twolpert]

I was wondering how changing Map Datums and coordinate formats affects stored waypoints? I typically use UTM when I am using my GPSr with a paper topo map and I think the ones I use most often are NAD27. If I mark a waypoint when I am in UTM and NAD27, what would happen if I tried to go back to that point while I was in NAD83 and Lat./Lon

The waypoint marks the same location regardless of the datum (WGS84, NAD27 CONUS, ...) or grid system (lat/lon, UTM, ...) you use to display the coordinates. The unit stores the coordinates in WGS84 internally and converts them for display. Put simply, you will always be able to navigate back to the waypoint no matter how the coordinates are displayed.

 

There are only two situations in which the datum and coordinate system matter:

 

a) When you use the information with a paper map. In that case, you need to display the coordinates in the datum and grid system used on the map.

 

When you enter the coordinates manually (rather than by marking a waypoint). In this situation, it is vital that the unit be set for the datum and grid in which the coordinates are expressed. By extension, this means that you need to pay attention when giving coordinates to somebody else. For example, when posting geocache coordinates, they are always given in WGS84 lat/lon (degrees and decimal minutes).

[+Redwoods Mtn Biker]

Also, be aware that while you can change the datum in many mapping software application, most GPS receivers will use WGS84 for data transfer.