AgLeader GPS 1100

Comparison of Several GPS Receivers - (Updated) October 12, 2006

We often get calls from HGIS users who ask why their maps are in error.
Most errors in maps are caused by user's expectations of GPS performance.
Misunderstood or improperly specified claims by GPS Vendors are the primary cause of these complaints.
Improper installation by the user of the GPS is the secondary cause of these complaints.
We test GPS receivers to their specifications and publish our reports.
We do not sell GPS Receivers, so our test reports are not biased.

When buying a GPS, check the GPS specifications
Look for important wording - For example, you may see "sub-meter accuracy"? Over what time period? Is it accurate for 7.5 minutes? Or a year? A large range of time periods are used when testing GPS receivers. For HGIS GPS mapping applications, we will be returning to the same locations year after year. We need GPS specifications for the long term.

How good is your confidence in the map? The word "Typical" is used to mean 50% the time; actual accuracy may be 5 times worse than "typical". Or is it a 95% confidence level used by surveyors for mapping. Specifications such as RMS, 2D-RMS, or HRMS are not usually used for mapping (If you double these particular specifications you may get an approximation of surveyors accuracy. So if the GPS specifies "2 meter RMS", you know it is about a "4 meter GPS".) Check for the specification approved by surveyors: "2DRMS-95%", also called HRMS-95% or sometimes just 95% confidence (look for the "95%").

Is the test period specified? The GPS satellite constellation repeats every 24 hours. Some periods during the night or day are better than other periods. To be repeatable, a test must run for a full 24 hours. Some testers only test a GPS receiver during the best times to make it look better than it really is.

Is the Datum specified for submeter GPS Receivers? Submeter GPS Receivers use different Datums, so you need to know what the GPS reference is. For example, WAAS is referenced to a Datum called "ITRF00" (the full name is "WGS84 ITRF2000"). Some GPS receivers, for example John Deere's StarFire, are referenced to the latest ITRF(In 2007, that would be WGS84 ITRF2007). Other GPS Receivers are referenced to NAD83. Different submeter GPS models use different Datums. Maps collected with one model submeter GPS may not have submeter accuracy when using a different model submeter GPS.

The Ag Leader GPS 1100:
Ag Leader started shipping the GPS 1100 in February 2006, an advance publicity campaign was started November 2005, and some units were recalled in April 2006.
Ag Leader has had a good reputation over the years, so we bought several of these units.

Advance Publicity: Nov. 2005 to Feb. 2006
(Catalogs, Price Sheets, and Advertising)

Revised Claims March 2006
(Dealer only email)

First Recall April 2006
(Letter to Customers)

Original Claim:
"Sub meter accuracy",
"Ideal for ... mapping."

"Correction to Listed Accuracy of GPS1100
Now that the GPS1100 has been released and we have had additional time to evaluate the accuracy of the system, our tests are showing that the unit is not providing the sub-meter accuracy performance we were expecting. Accuracies are closer to the 1.5-meter accuracy, pass-to-pass, that was found in last years model - GPS1000 Plus. Therefore, we have changed our specs on both the website and price sheets, removing the sub-meter classification. The product catalog will be updated when the next batch goes to the printer. The receiver still has the ability to output 4Hz NMEA , be used with DirectCommand's AutoSwath feature, and for outputting radar speed signals. As has always been the case with the new GPS1100, this unit is not recommended for guidance. If this change in accuracy classification affects any customers who have purchased the GPS1100, feel free to contact us and we will work with you and your customer to rectify the situation. We are sorry for any confusion this may have caused."

Second Claim:
"closer to ... 1.5 meter accuracy, pass-to-pass"

The serial number range of this recall is 2005860426 to 2006880165. The recall is to fix some units that may be having difficulty tracking the WAAS differential signal during certain periods of the day or locations in North America. (The WAAS system has recently undergone some changes, providing more satellites for increased coverage across North America.) This recall will accommodate those recent changes as well as provide improvements for better performance in general.
Due to the timing of this recall, Ag Leader will be replacing your GPS1100 free of charge as opposed to repairing the unit. If your GPS1100 falls in the above serial number range, please contact Ag Leader’s support department (support@agleader.com) and obtain an RMA number. Once an RMA number is obtained, the replacement GPS1100 will be shipped and billed on your account. When the old unit is returned to Ag Leader, a credit will be processed to remove the invoice from your account. This offer is valid until June 1, 2006.
Third Claim:
"We fixed WAAS"

The GPS 1100 specification should say
"When operating pass-to-pass with 7.5 minutes between passes, the Cross-Track-Error(XTE) of the GPS 1100 will be greater than 4.9 feet (1.5 meters) 50% of the time."
For mapping applications, the specification of the GPS 1100 should read "14 feet (4.4 meters) 2DRMS-95%".
The GPS 1100 is less than "Ideal ... for mapping." At the current time, AgLeader is still making this claim..
Your repeatability when returning at a later time is expected to be about 18 feet (95% confidence).

Our tests show that the reason for the first recall is that the early GPS 1100s contained an inferior patch antenna incapable of tracking WAAS.
AgLeader is now using a patch antenna that they consider to be an improvement for WAAS. (We tested the improved WAAS Antenna in the field below).
In our tests below, we tested the GPS 1100 at premium locations where we could track WAAS (we also know how to test a GPS for best results)
The first recall does not affect any of our test results, as we tracked WAAS 100% of the time in our static and dynamic tests.

Our Actual Tests:

WAAS STATIC TESTS Low Multipath Environment 100% WAAS Differential A submeter GPS would be within the red circle 95% of the time.	WAAS DYNAMIC TESTS 100% WAAS Differential One Hour Test = 1.9 meters from best average 95% of the time.

Actual Field Test with the WAAS improved GPS 1100.
There should be NO white space between swaths. Note that for a short time in the lower right two swaths are adjacent. White space means that the GPS was in error as we know the swaths didn't overlap.
Often the GPS 1100 error was an entire swath (20 feet). This matches our other test results.

Field Test

Static (Stationary) Tests
Carefully run static tests are the best indication of the performance of many GPS Receivers. We run our static tests in a low interference environment. If the environment is not ideal; interference at the test site can affect the test results that would not affect the GPS in the field. One common type of interference is called "Multi-path Interference". Some GPS Receivers can also have special features (such as "Pinning" or "Psuedo-range Tracking") which can affect testing. We carefully look at all these factors, and compare the static results with the dynamic results. Statically, the GPS 1100 was horizontally within 4.44 meters of WAAS (ITRF00) 95% of the time. Also statically, the GPS 1100 was horizontally within 3.72 meters of its own best 24 hour average 95% of the time.

Dynamic (Moving) Tests
We ran a one-hour dynamic test to verify the "vintage" of the GPS 1100 electronics and test features that did not show up in static tests. We compared the GPS 1100 using a Trimble AgGPS 132 as the reference GPS, and measured the error of the GPS 1100. Relative to the reference receiver, the GPS 1100 was within 2.4 meters of WAAS (ITRF00) 95% of the time. Relative to itself, the GPS 1100 was within 1.9 meters 95% of the time. We normally see smaller errors in the dynamic test because it is a one hour test compared to the 24 hour static test. GPS errors are localized over time periods shorter than 24 hours. We found that the GPS 1100 static tests were representative of its absolute dynamic accuracy. If we ran a 24 hour dynamic test, we would expect to see errors in the 3.7 - 4.4 meter range, as we did in our static tests.

WAAS Sensitivity (Before the April 2006 Recall)
The WAAS Sensitivity of the original GPS 1100 is very poor compared to other current generation GPS Receivers we have tested. WAAS sensitivity of the GPS 1100 is made worse by using the antenna's magnet mount. In areas where you cannot track WAAS, your repeatability will be about 21 feet (95% confidence). If the GPS 1100 can track WAAS in your fields, you can expect the 18 foot (95% confidence) repeatability that it is capable of with WAAS.

WAAS Sensitivity (After the April 2006 Recall)
The field plot above was with the WAAS improved GPS 1100. Using the Magnet Mount should still be a problem with the newer GPS 1100 receivers; if you raise the unit 12-16 inches above metal surfaces, it will improve its tracking of WAAS and the overall accuracy of the GPS 1100 to about 15 feet.

Run Your Own Tests
The demo version of HGIS GPS Mapping software (available at http://www.starpal.com/v800/HGIS_GPS_User.php ) can be used to run a one hour test on a GPS. The demo will run for one hour, but can be repeated as many times as you want. Start the demo with a "PRO All Features" profile; select Start GPS (Do not check the Save Files checkbox, as using this feature will cause pauses in the demo.). Open the GPS Statistics Screen (only available on the PRO profile) under menu GPS Misc Info..., and watch the accuracy statistics collect for one hour (it starts reporting after 10 minutes). If you check "Show GPS Trail", you can watch the GPS drift around on the screen while you are stationary (you need to zoom in with submeter GPS receivers). You can also try the other features of HGIS during the hour. With the GPS 1100, you will see a pattern similar to the dynamic test shown above right.

GPS 1100 Summary
The GPS 1100 looks to be very shock resistant. The cable is already fitted with connectors and has a cable shield. You can just plug it in. By default, it reports position once per second, but this can be changed to 4 times per second (4 Hertz) with supplied software. It has a simulated Radar output which we did not test.

HGIS users discover the GPS 1100 does not give advertised performance when they return to a mapped field. Unfortunately, the published AgLeader recall will expire before some users find out the actual capabilities of the GPS 1100.
If you purchased a GPS 1100 for use with StarPal HGIS GPS Mapping Software; Ag Leader is privately offering the following "No Questions Asked" (no time limit specified) refund because this GPS still does not meet its specifications.
We will keep you posted as Ag Leader further addresses this problem.

"[W]e will be contacting all the specific dealers, and customers if we have
that info, who we have sold GPS1100's to to inform them of the situation
and offer them the chance to return their units, no questions asked, if
they had intended to use the unit for operations requiring sub-meter
accuracy or guidance."  - AgLeader

Accuracy Specifications comparing several GPS Receivers:
Column in Bold is most often used to compare different models of GPS receivers.

	Cost	"Typical" (CEP)	"RMS" (1-sigma)	"2DRMS-95%" (2-sigma)	Your Expected 95% Repeatability*
Ag Leader GPS 1100 (Self Average)	$895	1.7 Meter	2.1 Meter	3.7 Meter	5.6 Meter (18.4 feet)
Ag Leader GPS 1100 (Compared to WAAS)	$895	2.3 Meter	2.9 Meter	4.4 Meter	6.6 Meter (21.7 feet)
Garmin GPS 18-5 Hertz (Self Average)	$199	1.2 Meter	1.5 Meter	3.2 Meter	4.8 Meter (15.7 feet)
Trimble Ag GPS 106 (Compared to WAAS)	$795	0.8 Meter	1.0 Meter	1.9 Meter	3.0 Meter (9.8 feet)
Trimble Ag GPS 132 (WAAS) Submeter GPS	$2995	0.25 Meter	0.34 Meter	0.71 Meter	1.1 Meter (3.6 feet)

* Expected Repeatability combines the GPS error of the initial measurement plus the GPS error when you return to that same location at a later date.

Alternatives For Mapping
We have two recommendations that will beat the GPS 1100 for less money. At $795, the Trimble AgGPS 106 is the GPS that the GPS 1100 claims to be. The Ag GPS 106 has a better antenna element than the GPS 1100 which will improve WAAS reception and reduce multipath intereference. It reports position at 5 Hertz. The downside is that it does not have a radar output (the accurary of the GPS 1100 radar output will be poor as the GPS jumps around as demonstrated in the field above.)

At $199, the Garmin GPS 18 5 Hertz will also beat the GPS 1100. The Garmin GPS 18 5 Hertz is available at http://www.garmin.com It is waterproof to one meter, has a rugged polycarbonate case, magnet mount, and reports position five times per second. Garmin calls the 2DRMS-95% specification "DGPS (WAAS) accuracy: Position: < 3 meters, 95% typical" and this is accurate according to our tests. The GPS 18 5 Hertz is more accurate than the GPS 1100 in all our tests. The GPS 18 needs a 5 volt automotive power adaptor available at any store with an automotive/electronics department such as Target($10), Radio Shack($17) or Wal-Mart, K-Mart, Best Buy, Circuit City as well. You must attach a Serial Connector to the cable end (available at Radio Shack) to match your computer. The Garmin cable meets industry standards for GPS cables. Your total cost of all parts including shipping should be less than US$250. The GPS 18 does not have the radar output as does the GPS 1100.

For submeter GPS alternatives, please review our report on submeter GPS Receivers at http://www.starpal.com/Reports/Submeter_GPS_Report_e.html

GPS 1100 internals:
The GPS 1100 contains a GPS engine rated by the GPS manufacturer at 2.0 meters "typical " (CEP).
As can be seen above, 2.0 meters CEP is in-line with our test results of 1.7-2.3 meters "typical" (CEP).
We inquired of Ag Leader about their specification being better than the GPS manufacturer's own specification,
this was Ag Leader's response:

"Historically we have been very conservative when listing accuracies of products so that
customers did not get the wrong impression about out products capabilities.
Over the last 3-4 years our competitors have done the opposite, often quoting accuracies that
could not be achieved but all the same made our offerings look inferior because we would not
claim such specific values." - Ag Leader

Perhaps being conservative is why Ag Leader has had such a good reputation?

We hope that this information aids in your choice of GPS Receivers.
http://www.starpal.com