Blog Archives

The Cohutta and Big Frog Wilderness Loop

2/1/2010

The Cohutta and Big Frog Wilderness Loop is the result of a Fall 2009, 95-mile exploration of the dirt and gravel roads in and around the Cohutta Wildlife Management Area in Fannin, Gilmer and Murray Counties, Georgia, and the Big Frog Wilderness in Fannin County, Georgia and Polk County, Tennessee.

The Cohutta and Big Frog Wilderness Loop.kmz file contains one 95-mile track and 78 waypoints (with a few photos). This track is a loop. The track begins and ends at the intersection of Highway 2/52/Chatsworth Hwy and Gates Chapel Road. There are a number of roads you can use to access the loop, this just happened to be our access point for this particular visit.

In dry weather, stock 2WD vehicles should have very little difficulty driving this loop, though portions of the trail may require careful tire placement. A high(er) clearance AWD vehicle would be quite comfortable on this trail. In wet weather, the loop may be considerably more interesting and likely would require a high clearance AWD or 4WD vehicle.

Download The Cohutta and Big Frog Wilderness Loop.kmz file.

-David

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Unpaved Georgia DOT and Forest Service Roads

2/1/2010

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The basis for much of my exploration in Georgia, this subset of GDOT's road network contains Forest Service (I believe most are FS) roads with Gravel, Compacted Soil, Native or Other Material Surface Types and with an Operational Maintenance Level other than Closed. Meaning? Unpaved roads that are also open (or potentially open). There are many roads that I have found closed, but are likely not permanently closed. For instance, some may be closed seasonally only to reopen once conditions improve and the likelihood for damage due to weather and usage diminishes. The GDOT and FS roads are symbolized in orange in order to differentiate between the basemap roads sourced through GDOT and those I have personally captured with GPS (in red, see Cohutta post).

Download The Unpaved Georgia DOT and Forest Service Roads.kmz file.

-David

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MotionX-GPS

2/1/2010

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Last summer I finally realized the joys of iPhone ownership. The iPhone 3GS I purchased has built-in GPS and a proper magnetic compass that appears to work well enough. Yes, the GPS is not the best. It would have been nice to see a WAAS-enabled SiRF StarIII (or StarIV) chip in there. Regardless, it works pretty darn well and has proven to be sensitive enough for offroad trail use with a significant tree canopy.

Accuracy
The positional accuracy of the iPhone GPS appears to be fairly good. Using the MotionX-GPS app (more about that in a moment) on my iPhone I captured a track and viewed it in Google Earth. I compared the captured track with a .kml overlay of GDOT roads, the NAVTEQ streetbase found in GE, and the GE (coarse) aerial imagery. In my unscientific eyeball and onscreen measurement test, the typical error I found for the captured track was in the 20-40ft range, based on the position relative to the road visible in the imagery. I'm not certain about the positional accuracy of the imagery. The NAVTEQ data appears to be quite close to the road centerline visible in the imagery, while the GDOT roads were generally worse, positionally speaking. The captured track had errors as great as 300ft in a couple areas, 50-100ft in others. For the most part, however, the MotionX-GPS captured track was well under 50ft compared to the street centerline viewed on the imagery.

MotionX-GPS
After testing a number of GPS apps, the one I finally settled on is the MotionX-GPS app by Fullpower. As of 1/17/10, it is only $2.99 on the App Store. I originally intended to purchase a newer, mid-grade GPS device to take on the trails. I was due for a modern, updated device with plenty of data storage after owning a couple older consumer GPS units. While the MotionX-GPS does not replace a new rugged handheld GPS for hiking or serious technical use, it does a fine job in a vehicle. The tracks and waypoints found on GeorgiaOverland are captured using MotionX-GPS and a 3GS iPhone. Read up on the app, see what you think. A couple highlights that I have found useful is the pre-caching of imagery/road tiles for use in the field and the ability to import .gpx files and export .kmz and .gpx files. In addition to an editable description (plus time, date, and more), the Tracks and Waypoints can include a photo, captured by the iPhone. The only drawback I see is that MotionX does not allow a full resolution photo to be attached to the location as it automatically saves the photo in a lower resolution.

Overall, MotionX-GPS is a capable app, and at only $2.99 it is a great value.

-David

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