This article was originally written in June, 2002. That's a time when GPS usage on the course was considered "cheating" and the packaging of hand-held and on-cart GPS devices was more primitive than it is today.
GPS is the common acronym for navigation systems based upon the military's Global Positioning System.
Though not specifically associated with the sport of golf, GPS has found a niche on certain courses and is used primarily to locate with fairly tight accuracy your position on a particular fairway.
Some golf carts are equipped with GPS displays (such as this one from ParView, click photo to enlarge), which present a graphic image of the course, offering you the ability to zoom in on your present position and distance from the green. Some units include fancy functions, such as the ability to display a trace (or track) of your entire "ballpath" for the round.
Addendum: From what we can tell, Parview appears to have been absorbed byProLink's parent company.
Course managers actually can use radio-transmitters on these same carts to view a map of all the carts on the course at any given time. This helps to focus the roving marshal on just those foursomes who are falling behind the accepted pace of play.
• • •
Of course, there are political concerns over the use of GPS on a golf course. Does it violate the Rules of Golf? After all, those electronic range finding binoculars are not legal for sanctioned play*. And if GPS can tell you how far the flag is from your current position, isn't that a violation?
Addendum: Thanks to the lobbying efforts of GPS and rangefinder manufacturers, The Rules of Golf were recently amended to permit the use of mechanical and electronic range-finding devices on the course as long as distance is the only metric being displayed. Technology which provides other information (such as inclination or wind data) remain illegal.
Well, the shocking thing is that many golfers are simplyrejecting the GPS system altogether, treating it as blasphemous. It has been difficult for many courses to convince customers to pay a premium to rent a cart equipped with GPS. Other golfers enjoy the graphic display of their game briefly. But soon the novelty wears off... particularly when bombarded by advertisements. Some even perceive that the distraction of GPS is slowing the game.
That said, there is still enough popularity for manufacturers to produce portable hand-held units such as this one fromXY Golf, or evensnap-on units with special software to work with off-the-shelf Palm Pilot handheld assistants.
• • •
The principle of GPS is actually based upon super-accurate time signals, broadcast over radio waves from a constellation of 24 satellites circling the globe. At any given moment, at least three satellites will be within range of every point on the planet, permitting a GPS receiver to triangulate its position to within 10 yards or meters.
Golf courses seek better accuracy than that and they use a modification of GPS called "Differential GPS".
Differential GPS involves the use of one additional time signal... one broadcast from a ground facility situated on the golf course itself! So a golf course equipped with highly accurate GPS will actually have a stationary broadcasting unit affixed to a pole or tower somewhere on premises.
The location of the stationary signal is known with great accuracy and its signal, when combined with those of the orbiting satellites, allows a golf cart GPS receiver to pinpoint its location to within a yard (meter) or so.
Even though GPS has been around for more than a decade, only recently has it been practical for use on the golf course.
Fearing that a hostile government might use our own Global Positioning System to aim missiles at The United States, the military had deliberately distorted the GPS time signals enough to reduce accuracy to about 100 yards (about 90 meters). In other words, your GPS unitcould tell you precisely where you were on the course... but couldn't say for certain that you weren't also 100 yards south or east or west or north of the position it "thought" you were at. So in those days a GPS unit might have placed you two fairways away from your true position! But that was still accurate enough for air and sea navigation, which was the original purpose for GPS, after all.
The military still has reservations about the misuse of GPS. But in the late 1990s, GPS accuracy was tightened tenfold to make it more useful commercially, particularly for automobile navigation. And highly accurate Differential GPS is now cheap enough (and portable enough) for even roving land surveyors to use.
• • •
If you're here, then you mustreally be wondering how the magic of GPS works.
Here's a general idea of the principle. To make it easier to visualize, let's describe it in just one dimension. In other words, we're going to imagine a very simple positioning system to help us locate where were are along a straight line, say a sidewalk that is two miles (three kilometers) long.
Imagine a day so foggy that you cannot see anything but the sidewalk underneath your feet and the wristwatch on your arm. You can see that you are on the sidewalk. But the question is:Where are you along its length?
You know that there is a sound beacon at one end of the sidewalk and another beacon at the other end. You are on the sidewalk somewhere between the two beacons.
Both beacons are synchronized to emit a loud chirp simultaneously. Each beacon has its own distinctive chirp sound so that by listening, you can tell which beacon sent the chirp that you just heard.
Each chirp will travel from the beacon along the sidewalk towards you at the speed of sound. If you are at the center of the sidewalk, equidistant from each beacon, then there is a mile between you and each beacon and each chirp will take five seconds to arrive at your ears. You will hear both chirps at the same instant. In GPS, as in our imaginary positioning systemit is not important how long it took for the chirps to reach your ears.
Whatis important is thetime interval between the chirps of the beacons.
You heard both chirps at the same instant. Therefore you know that your distance from each beacon is precisely the same and therefore you must be mid-way between them. That was easy.
But what if youaren't precisely mid-way between the beacons? Can you still determine where you are using the chirps? Let's see...
You pick a direction and walk along the sidewalk towards Beacon A. As you move, the beacons keep sending synchronized chirps, say one every few minutes. As you move closer to Beacon A, you begin to hear the chirp from Beacon A sooner than the chirp from Beacon B. The more you walk in the direction of Beacon A, the more time elapses between hearing the chirp from A and the corresponding chirp from B. After walking about ten minutes you pause to determine how close you are to Beacon A.
Using your watch, you measure the interval between the chirp from Beacon A and the corresponding chirp from Beacon B. Your watch says 'five seconds'.  Knowing how fast sound travels, you could create a formula, do the math and actually calculate where you were along the sidewalk.
Here is your formula: D = 1 - T/10
It means: Take the number of seconds between chirps and divide it by ten. Subtract that figurefrom 1 and the result is the number of miles you are from Beacon A.
Recall that our sidewalk is precisely two miles long. You heard the chirp from Beacon A. Precisely five seconds later you heard the chirp from Beacon B. Where are you along the sidewalk?
Use the formula. Take that 5 second interval and divide it by ten. That gives you 0.5. Now subtract 0.5 from 1 and you get 0.5 as the answer to the question. You are 1/2 mile from Beacon A.
Indeed, armed with two good ears, a stopwatch, calculator and the formula, you couldalways determine precisely where you were on that sidewalk from end to end even on the foggiest of days.
• • •
We needed to make certain assumptions in order for this beacon-based sidewalk positioning system to work:
1) We needed beacons and they had to emit their chirps at precisely the same moment
2) We needed a way to detect the chirps
3) There had to be a way that we could distinguish the chirp of one beacon from the chirp of the other
4) We needed to know where the beacons were situated (with respect to the sidewalk)
5) We needed a way to precisely measure the time interval between the chirps
6) We needed to know fast the chirps propogated through the air (how fast sound travels)
7) We needed a calculator and a formula to convert the measured time interval into a specific location
Guess what?
These are exactly the same elements of the Global Positioning System.
Of course, there are some differences between GPS and our foggy sidewalk system.
1) In GPS, the individual satellites replace our beacons. And radio wave chirps replace the sound wave chirps. And the chirps are broadcast many times each second rather than once every few minutes.
2) We used our ears to hear the beacon chirps. A GPS receiver uses a fat, stubby antenna to detect the satellite chirps.
3) Our beacons used chirps of different pitches so we could tell which chirp came from which beacon. GPS "chirps" actually carry a coded message that includes the identity of the satellite.
4) We knew ahead of time where the beacons were situated with respect to the sidewalk. Part of the information within each satellite's "chirp" is its location with respect to the Earth.
5) We used a stopwatch to measure the time interval between chirp arrivals. Your GPS receiver (whether it be handheld or mounted upon the golf cart) has an internal clock to measure the time interval between corresponding GPS chirps from different satellites.
6) GPS "chirps" travel at the speed of light instead of the speed of sound.
7) The GPS receiver also contains a microprocessor and memory so that it can remember the formula and calculate your position (latitude, longitude and altitude). It converts the time intervals into a "fix".
Now in our foggy sidewalk experiment, two beacons were sufficient for our system because we limited your excursion to the boundaries of the straight sidewalk. Were you to stray from the sidewalk or even climb a tall tree, you'd find that two beacons would not be enough.
In the real world, your GPS receiver needs three and sometimes four satellites to obtain a three-dimensional "fix" of where you are. And to ensure that there are always at least three satellites within your vicinity at any moment in time, our government has launched 24 satellites in a special arrangement of orbits called a "constellation".
Additional GPS satellites are in orbit to serve as spares. Andall of these satellites are constantly tuned so that they continue to emit their "chirps" in a synchronized manner, many times each second.
• • •
So there you have it. And weknow that it must be raining today. Otherwise you'd be out golfing rather than reading this long-winded treatise about GPS's use on the golf course. |
