How to project a waypoint with greater precision than 0.1km (or 0.1mi)

Firstly, these instructions work equally well for kilometres, and miles, and are interchangeable. However, 1/10 of a mile is equal to 528 feet and 1/100th of a mile is 52.8 feet (while 1/10th of a km is 100 metres, 1/100th of a km is 10 metres, etc.) 1 metre is equal to 3.28 feet, while a foot is equal to 0.3048 metre. Hence in this example, 50 metres are equal to 264 feet. The arithmetic requires a bit more mental juggling in statute measurements.

Note that while this procedure allows you to go down to 1/100th of a km, or to metre accuracy (or down to1/100th of a mile or 53 feet), it won't be of much value since most commercial gps error is to the order of to 6-10 metres or more, depending on local conditions and your sampling technique.

Example You want to project 382m at 50

As for the question at hand, the short of it is that you can't program down to less than 1/10th of a km or 1/10th of a mile, unless your gps either has a software upgrade for it or comes that way.

  • choose the waypoint you've just set.
  • instead of choosing to navigate to that point ("goto" on your yellow etrex) choose "project"

    At this point you have three choices:

    Course #1

    Use linear interpolation to find your actual waypoint.

  • Project 0.3km at 50, let the resulting coordinates be lat1 and lon1
  • Project 0.4km at 50, let the resulting coordinates be lat2 and lon2
  • Estimate your waypoint as lat = lat1+82/100*(lat2-lat1) and lon=lon1+82/100*(lon2-lon1)

    Put more generally, if you want to project a distance of n*100+x m, project the points at n*100 and (n+1)*100m and interpolate coordinates as c=c1+ x/100*(c2-c1)

    Even more generally, you can replace the "100m" by whatever the resolution of your device is.

    If your arithmetic isn't good but you're comfortable using your gps in the field:

    Course #2

    project 0.4 km bearing 50 degrees. set your gps to display your bearing walk to the newly created waypoint when you get to within 18 metres of your waypoint, concentrate on your bearing, and walk about, while maintaining 18 metres distance, until your waypoint is 18 metres ahead of you and its bearing is 50 degrees.

    Course #3

    project 0.3 km 50 degrees. set your gps to display your heading walk to the newly created waypoint continue walking beyond your waypoint, with your gps pointing behind you while maintaining a heading of 50 degrees. You have arrived at your new location when your gps states that your waypoint is 82 metres behind you and its bearing is 310 degrees.