For GPS/GNSS tech-weenies only

[Puck]

I was given those coordinates and told they were from a GIS format. WHile playing around with the Garmin software "Mapsource" I found how to change the format from DD MM SS to DD.DDDDD as DougPaul explained. I entered the coordinates as waypoints and found that there is a route that is slightly off the trail. What they need is to have somebody "me' go out and get actual GPS coordinates marked from the trail.

The amount of experitse you guys have is amazing.

 

[DougPaul]

I was given those coordinates and told they were from a GIS format. WHile playing around with the Garmin software "Mapsource" I found how to change the format from DD MM SS to DD.DDDDD as DougPaul explained. I entered the coordinates as waypoints and found that there is a route that is slightly off the trail. What they need is to have somebody "me' go out and get actual GPS coordinates marked from the trail.

If the route is slightly off trail, it is possible that you are using the wrong datum. IIRC, the difference between NAD27 (used on many USGS topos) and WGS84 (native to the GPS) is ~220 meters in the Whites.

The GPS and Mapsource use WGS84 internally and in their datafiles. When you set a datum on either, it just converts for screen/keyboard I/O.

A simple way to estimate the difference between two datums is to set a waypoint using datum 1 (near the location of interest) and then set another waypoint with the same numerical coordinates using datum 2. Then use the distance measuring function in Mapsource to measure the distance and direction between them. (This can also be done on the GPS, but it is easier to do in Mapsource.)


BTW, one way to set a waypoint to some numerical lat and lon in the GPS is to set a random waypoint and hand edit the coordinates on the waypoint description screen. It will then "jump" to the specified location. Make sure that you have the datum and format set correctly when doing this.

Doug