20 km hike to GPS all the trails at Reynolds Nature Preserve in Morrow/Lake City, Georgia, USA. Used a Garmin GPSmap 62s with external amplified GPS antenna. Trails and other features added.
OpenStreetMap
20 km hike to GPS all the trails at Reynolds Nature Preserve in Morrow/Lake City, Georgia, USA. Used a Garmin GPSmap 62s with external amplified GPS antenna. Trails and other features added.
Discussion
Comment from maven149 on 2 February 2015 at 04:05
Like the one below: http://www.amazon.com/GARMIN-010-10702-00-GPS-Antenna-Kit/dp/B000BS2V80/ref=sr_1_fkmr0_1?s=electronics&ie=UTF8&qid=1422849798&sr=1-1-fkmr0&keywords=external+gps+antenna+garmin+GPSmap+62s
Comment from maven149 on 2 February 2015 at 04:52
Accuracy is relative. I use an external amplified antenna while recording tracks to free my hands and avoid blocking satellites with my body. The antenna is mounted on top of a pole I made from 1” PVC tube that I have attached to my day pack so the antenna is a little above my head. That ensures I get at least the nominal 10 m accuracy of my GPS 95% of the time. To get better than that requires re-walking the same parts of a trail two or more times, normally just at intersections or points of interest, and visually averaging the lines when digitizing (most GPS traces with my set-up are within 5 m of each other when walking the same trail).
Then there is the 5% of the time that the signal goes wild, going off target 15 m or more (worst I’ve seen is 30 even with my set-up). That requires a more extensive re-walk and ignoring the track that is far from the others when digitizing on OSM. Oh, and it is important to mark waypoints at all trail intersections to serve as a guide to know if two more-or-less parallel tracks are different trails or the same trail. Waypoint averaging is needed when waypoint accuracy is vital but that takes several minutes and normally is not needed unless successive points are close to each other (within 10 m).
The estimated accuracy given on a GPS is wildly optimistic. But it is a somewhat OK measure of relative accuracy. Mine usually says 3 m with my set-up but I know it is rarely really that good under tree cover. Yet when it says 7 m or larger, I know that it is probably worse than normal. Oh and WAAS/EGNOS SAS correction that can give 3 m or better accuracy - forget about it under tree cover and/or terrain that blocks the southern horizon; you lose the signal often but the GPS still re-calculates based on the old data, which can lead to really bad traces (dozens of meters off sometimes).
This is the actual antenna I used. It is less expensive and, if the reviews can be trusted, better than the Garmin version. http://www.amazon.com/Powerful-External-Amplified-Antenna-Receiver/dp/B000ZKUR1W/ref=sr_1_fkmr0_3?s=electronics&ie=UTF8&qid=1422851068&sr=1-3-fkmr0&keywords=external+gps+antenna+garmin+GPSmap+62s
Comment from maven149 on 2 February 2015 at 05:00
s/SAS/SBAS = satellite-based augmentation system http://en.wikipedia.org/wiki/GNSS_augmentation#Satellite-based_augmentation_system