Comparing a GPS vs. SmartPhone, Part 2 of 2

04-22-2011 08:21 AM
Esri Notable Contributor
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Recently, I wrote about my comparison of the horizontal position obtained from a consumer-grade GPS receiver versus that obt.... Specifically, I compared a Garmin GPS 76 to an iPhone 4. The position recorded on my iPhone was consistently tens-of-meters off from the position recorded with my GPS receiver. Thus far, it appeared that my position as recorded by my GPS receiver is far more accurate than that from my iPhone. However, this was not the end of the story.

In the field, I switched to the map view on my phone, and the blue dot marking my current position was not hundreds of meters away, but just a few meters from where I was standing. I took a photograph here and emailed it to my PicasaWeb account using the procedures I wrote about in a previous blog column.

This photograph was geotagged at 39.680000 north latitude, 104.962667 west longitude, which turned out to be only 6.21 meters away (this time to the southwest) from my position as recorded by the GPS receiver. Interesting! This means that the SmartPhone was indeed recording an accurate position, but perhaps the app used to capture that position may have compromised that position.

The map I created from ArcGIS Explorer Online below shows my hyperlinked photograph very near to the position where I conducted the experiment, and several blocks to the northwest is the position recorded by the default compass utility in my phone.

Zooming in, Pushpin A at the end of the green line points to where I stood at the brick wall on campus. Pushpin B, 5.23 meters north-northwest, is the position recorded with my GPS receiver, and Pushpin C, 6.21 meters to the west-southwest, is the geotagged position recorded in the photograph I took at that spot.

Your results will vary with the tools, including the types of WebGIS, GPS, and SmartPhone used. For example, a higher-end GPS such as a Trimble or TopCon will surely provide better horizontal accuracy. Also, would my iPhone position have been any better if I had used a GPS app instead of the default compass tool in my phone?

All of these technologies will continue to undergo rapid change, providing ample opportunity for further experiments. These types of experiments connect mathematics, GIScience (including discussion on datums, coordinate systems, and data quality), and geography. How might you turn these activities into teachable moments and activities?

- Joseph Kerski, Education Manager
About the Author
I believe that spatial thinking can transform education and society through the application of Geographic Information Systems for instruction, research, administration, and policy. I hold 3 degrees in Geography, have served at NOAA, the US Census Bureau, and USGS as a cartographer and geographer, and teach a variety of F2F (Face to Face) (including T3G) and online courses. I have authored a variety of books and textbooks about the environment, STEM, GIS, and education. These include "Interpreting Our World", "Essentials of the Environment", "Tribal GIS", "The GIS Guide to Public Domain Data", "International Perspectives on Teaching and Learning with GIS In Secondary Education", "Spatial Mathematics" and others. I write for 2 blogs, 2 monthly podcasts, and a variety of journals, and have created over 5,000 videos on the Our Earth YouTube channel. Yet, as time passes, the more I realize my own limitations and that this is a lifelong learning endeavor and thus I actively seek mentors and collaborators.