Sugarloaf Peak + Old Sugarloaf Peak – Santa Ana Mountains – Cleveland National Forest – Orange County – California
Total distance: 9.91 mi
Max elevation: 3399 ft
Min elevation: 2729 ft
Total climbing: 3428 ft
Total descent: -3422 ft
Average temperature:
Download file: 02-11-2012-Sugarloafs.gpx
Max elevation: 3399 ft
Min elevation: 2729 ft
Total climbing: 3428 ft
Total descent: -3422 ft
Average temperature:
http://thistrail.com/gpx/02-11-2012-Sugarloafs.gpx
(3988)
Map makers post Sugarloaf at 3,227′ and Old Sugarloaf at 3,326′. Your GPS posts them at lower elevations — is that because of the weather affecting your unit? Wondering why distances for this hike also vary from GPS unit to pedometers and cell phone apps. It was an enjoyable 5hr day hike, glad we were able to complete the hike despite the weather!
The reported GPS differences has been annoying me for a while, so I finally decided to dig into this issue today. I don’t have an explanation for the distance differences, but I did figure out why the elevations reported in the screen shot of the Google Earth GPS track reports different summit elevations than the topo maps. It turns out that it is because of Google Earth! The raw track data from the GPS is quite accurate, within 30 feet of elevation on those summits.
When importing a track to Google Earth, you are prompted with checkboxes for 3 different import options. One of those options instructs Google Earth to reset the elevation in the track to the elevation of the terrain at any given point in it’s geography database. This option is enabled by default. On this particular trail (and likely most if not all trails) the Google Earth database has some elevation inaccuracies. This results in an incorrect elevation profile when displayed as an elevation plot in Google Earth.
I’ve added a new photo to the Sugarloafs Photo Gallery of a Google Earth track without this adjustment and the reported elevations are much closer to those reported by topo maps.
Incidentally, without Google Earth’s adjustments, the total elevation gain is slightly higher than the adjusted track while the total distance is slightly shorter.
Thanks for catching that. One less GPS error to worry about!
Also to follow up more on the difference between hiking GPS, cell phone GPS, etc. Many hiking GPS units contain a barometric altimeter to augment elevation tracking. Cell phone GPS units typically rely entirely upon elevation computed by GPS satellite signal.
My guess would be that the barometric altimeter produces smaller fluctuations than elevation data derived purely from satellite signals. GPS precision also degrades further when plotting in three dimensions instead of just two. Since hiking is a very 3 dimensional activity, especially upon steep climbs where the trail inclination can exceed 45 degrees (making elevation measurement more significant than horizontal position on the earth), inaccuracy in elevation tracking can lead to incorrect distance tallies.
Hiking GPS units which contain a barometric altimeter, usually have several options for how GPS elevation data and barometric elevation data are reconciled and integrated into the reported elevation. The above factors along with variations in barometer accuracy, GPS antenna design, weather changes during the hike, the specific logic for reconciling satellite vs barometer data, as well as the active barometer configuration option likely all contribute to the differences we see across different GPS units on the same hike.
Hopefully with time, the devices will improve and we will see fewer differences.
One further note on the elevation plot shown on this page: I am not sure why the elevation plot shown above shows such a difference from the actual GPS track data. There is likely some flaw or issue with the Google Maps plugin when plotting the elevation graph (further evidenced by Sugarloaf appearing to be of higher elevation than Old Sugarloaf on the graph.) I will look into that.
If you save the raw GPS track by right clicking on the GPX file link under the map and elevation plot, then open that plot in Google Earth, if you view elevation data (by right clicking on the loaded GPS Track in the My Places panel and choose “Show Elevation Profile”), it will report the correct elevation data so long as you did not check the box for “Adjust Altitudes to ground height” when importing to Google Earth.