GPS

Shifting Without Datum Documentation

By Casey J. McLaughlin

Most of us take for granted that latitude and longitude always mean the same place on a map but is that true?  I started thinking about GPS points and how a simple hand held (or my phone) may have an error of +/- several feet.  Now I am wondering if the fuss I make about specifying Datum is worthwhile….

Claudius Ptolemy: The World, 1482 (Wikipedia)

A Datum, defined by Webster’s is generally “something used as a basis for calculating or measuring.”  Ah ha! I had never thought outside of the geographic usage of the word but I find understanding word roots can be quite helpful.  What I really mean is what impact a Geodetic Datum has on latitude/longitude pairs.  A Geodetic Datum is “the reference point for the various coordinate systems used in mapping the earth” (Geography.about.com).  The Earth isn’t perfectly round and geodetic datums form the mathematical basis for modeling our home.

Meades Range Marker, Kansas (geocaching.com)

There are several datums which I see most frequently; NAD27, NAD83, and WGS1984.  The NAD27 (North American Datum 1927) is interesting from a Region 7 perspective because its origin point is a survey point in Kansas – Meades Ranch (approx. 39.224087, -98.542152).   Just for reference, the geometric center of the contiguous U.S. is also in Kansas! Once we began using high precision remote sensing technology, we needed a new datum – NAD83 (North American Datum 1983) was born.  NAD83 has its origin defined by the Earth’s center of mass.  The two systems are different enough that a given latitude/longitude could be several meters off – depending on the distance from the datum!  Today, the World Geodetic System (WGS) 1984 Web Mercator is commonly used – I believe most major web platforms use it.

The main point I’m getting at here is that documenting the coordinate system information of geospatial data IS important.  I have seen more than one dataset come in without proper documentation.  To map it, I have to assume what datum is used – it wasn’t recorded.  Please, if you’re collecting spatial data, don’t complicate it with incomplete information!  Documenting our data collections is vital for using data with confidence and ensuring future data reuse.

For more information on Geodesy and such, check out:

Casey McLaughlin is a first generation Geospatial Enthusiast who has worked with EPA since 2003 as a contractor and now as the Regional GIS Lead. He currently holds the rank of #1 GISer in EPA Region 7′s Environmental Services Division.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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Happy Belated Veterans Day: GIs and GPS

By Joe Summerlin

A few years ago, I found myself trekking along Town Branch Creek in Bolivar, Missouri noting areas that were impaired, taking photos, and storing waypoints on my smartphone. I mused at how easy it was to load information and tell a story about this little watershed from a device that fit firmly in the palm of my hand. Then it dawned on me. Just fifteen years earlier, I had witnessed the birth of handheld GPS devices in the U.S. Army. I then thought, “I am getting old. Maybe some of the younger generation would like to know about the predecessor to devices they take for granted today.” This blog will discuss the capabilities of handheld GPS devices in the early 1990’s, specifically the Precision Lightweight GPS Receiver (PLGR.)

The PLGR or “plugger” was one of the first mass produced handheld GPS devices used by conventional forces in the U.S. Army. It saw its first real combat test in 1991 during the Gulf War. The concept was simple: use existing military and secure government satellites to orient a soldier on the battlefield. At the time there were 24 satellites in orbit and this puppy needed three for accurate lat/long data or four for lat/long plus elevation data.

Many of the negative characteristics of the design of this beast were made by engineers to ensure longevity and meet the requirements set by U.S. Army leaders. Note the lack of a full color display. This was designed on purpose using liquid crystal displays to ensure an ambient light source would not give away the positions of soldiers on the field. This also made it incredibly difficult to read where you were. The display was also compatible with night vision goggles. Unfortunately, I always peeked under my goggles and pushed the “light” button or used a red-filtered lens and shined it on the display.

The PLGR was bulky, boxy and not a product to sell to the masses. The buttons were clunky and there were only twelve. In order to store a waypoint you had to arrow through a bunch of poorly written menus. Sometimes when you wanted to store a waypoint, you would find yourself scrolling through a menu for 10 minutes. When you did actually store a waypoint, you would have to clunk your way back to the main menu by using a series of guesses, some luck, and maybe some sort of magic ritual. My secret was to hit the power button and wait for the 7 minute reboot.

I haven’t even touched on the size of this monster. Hand held – yes, only if you had Shaquille O’Neal-sized hands. The PLGR weighed a mere 2.75 pounds or about the equivalent of one canteen of water.

The PLGR was large for two reasons. First, micro technology was not as advanced, and second, soldiers lose small items. It used 634 AA batteries (maybe it just seemed like it did) and the battery life was about 2 hours. We learned to conserve battery power by turning it off and using the maps in our pockets. Only when we were lost (which never happened because we are the U.S. Army) did we pull it out to get our bearings.

Well, there you have it, the smartphone’s grandpappy. Next time you are in the car listening to that speak n’ spell voice demanding “TURN RIGHT,” just think to yourself, if it weren’t for the military and those veterans that tested and used this stuff I might have just made a left turn at Albuquerque.

 

Joe Summerlin is an Environmental Scientist in EPA Region 7 who works with the Agency’s NEPA program. He served in the U.S. Army for 14 years as a Cavalry Scout and a CH-47D Chinook  helicopter pilot.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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New Place, New Signs

By Jeffery Robichaud

Yesterday was the first day in the new office.  My things all arrived.  I have unpacked.  I found the restroom.  For those of you who were left with a cliffhanger based on my last post, this is my view out my new window (which actually looks out on a window which looks out on the windows across our courtyard).

In a meeting yesterday our Regional Administrator told Senior Staff about his trip to Joplin Missouri last week for an event with the City marking the additional funds EPA is providing for sampling and remediation of contaminated soils disturbed by the May 2011 Tornado.  It didn’t show in the directions he generated online, but the RA certainly noticed the lack of street signs as he doubled back a few times before making the correct turns to arrive at the event.  The city is doing a wonderful job rebuilding, but with 2000 signs to replace, the City has had its hands full.

Driving in to our new office yesterday in the dark, to a part of the metropolitan area that I rarely visit, I really had to pay attention to the signs without the benefits of the few landmarks I knew to help guide me.   It got me thinking, is reading street signs starting to become a lost art, just like reading a map?  The proliferation of GPS in cars and phones now give you turn by turn directions.  GoogleMaps or BingMaps will give you a route with turn by turn instructions and even provide you with streetside views of those turns and your destination.  Some GPS units let you even choose the voice (one of the guys here has Darth Vader…he says for his kids but I’m not too sure).

With the explosion of these devices, for those of you with kids, do you think you could hand your own kids a map and have them navigate while you drove?  I know my Dad would hand us the maps while on vacation to help navigate (partly I’m sure as a way to keep my brother and me from fighting).   Are navigation instructions from hand held devices keeping us from making sense of maps and even leading us in the wrong direction? 

My wife and I started watching a new show called Revolution a couple weeks back.  In a nutshell, it is a post-apocalyptic world, if the apocalypse was caused by all electricity ceasing to be.   The characters do quite a bit of walking and one character says to the other, something to the effect, “I’ll meet you at this small town in Indiana in a couple weeks.”  In last week’s episode, while more walking was taking place, the second character pulls out a crinkled paper map to check their progress.  It wasn’t lost on me that this character’s back story was as an executive at Google.  Just another reason to teach your kids how to read a map.

About the Author: Jeffery Robichaud is a second generation EPA scientist who has worked for the Agency since 1998. He currently serves as Deputy Director of EPA Region 7′s Environmental Services Division.  He will miss his view of Kaw Point.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

Please share this post. However, please don't change the title or the content. If you do make changes, don't attribute the edited title or content to EPA or the author.