The DeLorme Weblog

Since we’re one day away from the Cache-In Trash-Out Geocaching Event I wanted to write another post about geocaching with your PN-20. While seeking a cache is a lot of fun, my experience with the Bears In The Bushes cache has taught me that hiding a cache can be even more exciting!

Since, arguably, the most valuable clue for a geocache is the cache coordinates, it is important to post a reading that is as accurate as possible. The waypoint averaging feature available on the PN-20 will help you increase your cache coordinate accuracy by calculating a rolling average as you gather GPS readings for a given location.

When you create your geocache waypoint, you will see an Avg (average) button at the bottom right corner of the page.

Press this button to display the Average Page showing GPS information, including the number of readings and the estimated accuracy for the location. Allow the waypoint to average until the change in estimated accuracy slows down. I don’t have a firm number but try to average for at least 100 readings.

The key to getting your best location coordinate is in returning to the same location over several days and at different times of day to update your GPS average. Returning over several days increases the random nature of your readings… Since your GPS device is influenced by the location of the satellites sending signals and by the atmosphere those signals travel through, it’s best to repeat your readings to average the environmental conditions with the readings on any given day.

To continue averaging when you return to your cache location press the Menu button and then choose Average Waypoint…

This will display the Averaging Page and continue to gather GPS readings to include with the values gathered during your previous visit.

Don’t worry if your estimated accuracy goes up when you first start. The device is averaging readings for the same location but with different environmental influences… that’s why we need to average over multiple visits. When you view your waypoints in Topo USA, you’ll be able to see the benefits of averaging over multiple days. The location of your cache will move with each update. If the cache location doesn’t move or moves only a little, you’ve averaged well and are ready to complete your listing!

Here is a link to some very informative GPS accuracy and averaging research by David Wilson, a mathematician from Kent State University.

Let me know if you have any questions about getting the best location information for your geocaches…

-Chip