How Accurate is Your GPS

Just how accurate is your GPS?

The package says that your Global Positioning System (GPS) receiver is accurate to +/- 15 meters and some advertise +/- 3 meters.  Just what does that mean to you?

Accuracy depends on several things, most of which are beyond your control.  For example, it is reasonable to expect a new GPS with the latest antenna, circuitry, processor capability and memory technology will perform better than one made in 2005.  The number of satellites signals a receiver acquires helps too; you’ll need at least four.

The graphic below tells an interesting story. 

Through the center of the topographic map, marked with dashed lines is the Pacific Crest Trail (PCT) in Oregon’s Cascades mountain range.  Next to the trail is my track log (in red) downloaded from my GPS to my Terrain Navigator software.  The track log is my electronic path calculated by the receiver. 

I walked on the PCT the entire time.  My GPS receiver was in a holster attached to the shoulder straps of my backpack.  The receiver’s antenna was exposed but only received data from my front and straight up, my chest blocked signals from behind my back.

As the green of the map indicates I was in a forested area. Tree canopy was moderately thick and may have interfered with signal reception.

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