The"frontier" of GPS precision ag technology is implement steering. Pioneered by AutoFarm with their AFTracker product, the idea of implement steering is based on the observation that, while the tractor may be within an inch of the line, the implement may not be.
Implement steering may seem like "overkill" to many, but there are a variety of applications for which it is vital. It is finding a great deal of use in potato farming, especially in hilly regions, as well as seed corn operations where the operator must be able to plant precisely between already-planted rows.
There are, essentially, two forms of implement steering, passive and active.
Passive implement steering products have been mentioned by Trimble, AutoFarm, and John Deere; they depend on "over-steering" the tractor to keep the implement on-line. With passive steering, the tractor steers wherever it needs to (perhaps well off the line) in order to keep the implement on the line. This may be a good approach for tillage and planting, but may be problematic for cultivation, application, or harvesting. No passive implement steering products are available currently. Both use coulters from Orthman's Tracker IV system to actively steerthe implement and keep it on-line. The upside of this is that the implement and the tractor remain within an inch of the line; the downside is that you have to outfit the implement with GPS equipment and the Orthman coulters.
Suppliers: Trimble implement steering system and the AutoFarm AFTracker
One of the most annoying things about using RTK is that, if one of the elements of the positioning system is lost for a moment, the position is lost and the system comes to a halt. Deere has addressed this with their "RTK Extend" capability, which uses the SF2 DGPS system to correct the GPS signal for a period of time if the RTK data source (the signal from the base station) is lost.
This doesn't seem like it should work, but it's based on the fact that even DGPS is very accurate for a short while. So, if you have a good position fix within an inch, then you can keep going within an inch or so using the DGPS source for several minutes before the DGPS "drift" will exceed an inch. If, by then, you have re-acquired the RTK signal, you can then continue using that for sub-inch accuracy.
AutoFarm's RighTrac system, although not a sub-inch system, uses a similar capability called "Reflex," although AutoFarm doesn't offer much information about it. It uses WAAS to supplement the near-RTK GPS solution.
Every so often a new GPS vendor comes to our attention.
Even though we know nothing about this company, AgGuide in Australia is in this market and, assumably, interested in your business.
Leica, a major European GPS vendor, has introduced their MojoRTK system, a lower-cost RTK system that's just being introduced in the U.S. An interesting feature is that the cab computer has a relatively small screen, and an integrated cellular modem. The cellular modem allows the cab computer to contact the internet, download software updates, and possibly perform other functions.
The purpose of this area is to provide additional information that we couldn't get onto the DVD for one reason or another. In many cases it's amplification or additional background for topics on the DVD; in some cases it involves topics that might have been on the DVD but just got cut in the interest of not having the DVD go on forever.
It's impossible to give a complete explanation of the GPS system in such a short time, and there are a number of excellent websites that offer very easy-to-understand explanations of how GPS works.
In almost all matters, my first stop would be at http://www.wikipedia.com - for GPS there's an outstanding entry at http://en.wikipedia.org/wiki/Gps
Another good "all-around" resource can be found here: http://edu-observatory.org/gps/gps.html
A very simple tutorial pertinent to farming can be found here: http://www.ext.vt.edu/pubs/bse/442-503/442-503.html>
Trimble offers a very nice tutorial on GPS here: http://www.trimble.com/gps/index.shtml
-Garmin also offers a very nice tutorial on GPS here: http://www.garmin.com/aboutGPS/ and a very helpful guide for beginners here: http://www.garmin.com/manuals/GPSGuideforBeginners_Manual.pdf
Another good all-around resource (but not necessarily for the beginner) is "GPS World" magazine and their web site at GPSworld.com
Of particular interest is an article in GPS World magazine about standardizing an approach to measuring GPS accuracy- see the article at http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=399847
Did my one-minute class on statistics give you everything you wanted to know, or do you still want more? If you want more, here are some good resources:
http://home.comcast.net/~brooks50/stat_smp.html - a basic tutorial with more of a medical approach
Wikipedia's entry on the Standard Deviation is useful - just blow past all the math formulas: http://en.wikipedia.org/wiki/Standard_deviation
You can find some good explanations of DGPS here:
Wikipedia (of course): http://en.wikipedia.org/wiki/Differential_GPS
Another explanation:http://www.esri.com/news/arcuser/0103/differential1of2.html
More information about coast guard beacons can be found here:
>http://www.navcen.uscg.gov/dgps/default.htm<
The CORS and Cooperatvie CORS system is described here:
http://www.ngs.noaa.gov/CORS/ and http://www.ngs.noaa.gov/CORS/Coop/
Additional info: Some of the Cooperative CORS base stations use RTK-capable base stations and create RTK data streams in CMR format (the most common format for RTK data). There are some growers who have made an agreement with their local Cooperative CORS site to have them "stream" the real-time RTK data on the internet. They then get this data to their vehicleâs GPS system that pulls the data from the internet through the cellular phone network.
It's a neat trick, but hard to set up and only practical if you live close to a suitably-equipped Cooperative CORS site and have good cell phone data reception in your fields.
The official WAAS site is here:http://gps.faa.gov/programs/waas/waas-text.htm.
One of the most useful tools I have found on the internet are these maps, showing the Dilutions of Position (DOP) for WAAS. They show where WAAS is and is not useful. The most interesting is the Horizontal Dilution of Position map:http://www.nstb.tc.faa.gov/npa.html
See other links at the bottom of that page.
OmniSTAR offers a variety of web sites and other resources. Some things we have found useful:
Main page: http://www.omnistar.com/
Technical information (of particular interest is the "coverage maps" link to see where OmniSTAR can be used): http://www.omnistar.com.au/techinfo/techinfo.html
One of the significant negatives about OmniSTAR is the convergence time - it typically takes 20-50 minutes to get a precise position fix using OmniSTAR XP or HP. A good presentation on convergence and convergence times for OmniSTAR can be found here (warning - this is a 9 MB PowerPoint file): http://www.navcen.uscg.gov/cgsic/meetings/EISubcommittee/2005_presentations/22%20ORBCLK%20PRA.ppt
There is significant doubt about what is actually gained by paying the extra money for OmniSTAR HP over OmniSTAR XP. Take a look at the last two questions in this FAQ, and you'll be as confused as I am: http://www.fugroseastar.com/8300faq.html
Trimble claims that there is some small difference, however: http://www.trimble.com/aggps332.shtml
John Deere doesn't have a lot of information available about the SF1 and SF2 systems. What's available is here.
Chart outlining SF1 and SF2 precision (note that no timeframe is provided; since this is DGPS, assume these are "pass-to-pass" figures, measured over 15 minutes): http://stellarsupport.deere.com/en_US/support/atu/ATU_Component_Chart.html
At the bottom of this page is a chart with SF2 pricing and a statement that the SF2 precision figures are, in fact, pass-to-pass: http://www.deere.com/en_US/ag/servicesupport/ams/mobilecomponents.html
John Deere's GPS technology subsidiary, NAVCOM, has some more information about StarFire here: http://www.navcomtech.com/StarFire/
There is a real dearth of good, simple explanations of RTK; some additional information can be found here
Wikipedia: http://en.wikipedia.org/wiki/Real_Time_Kinematic
Trimble's short explanation can be found here: http://www.trimble.com/ag_gps.shtml
Everything else I can find really requires a Master's degree in engineering to make much sense.
Radios are a particular interest of ours. Some of the common data radios being used in GPS RTK systems are
FreeWave - http://www.freewave.com/ - a Colorado company that makes license-free 900 MHz. Spread-spectrum radios, used by John Deere, AutoFarm, and others
Satel - http://www.satel.com/ - Finnish company that makes 450 MHz (and other) data radios used by several vendors
ARWest - http://www.arwestcom.com/ - California company that makes data radios for several different frequency ranges; used by some of the leading vendors
Pacific Crest http://www.paccrst.com/ - now a division of Trimble
A very good guide to setting up an RTK base station (although not intended for agriculture) can be found here: http://www.paccrst.com/downloads/guides/M00053-Guidetogps.pdf
The single piece of advice that anyone can offer you for siting the base station for an RTK system is, "put the transmitting antenna higher."
We only touched on RTK networks, but they should become increasingly important over time. Some RTK networks are just RTK base stations that are positioned so you can obtain data from the closest one wherever you're working. Others use networking and averaging to provide a "customized" RTK datastream to your vehicle. One such example is the "Virtual Reference Station" or VRS. A good explanation can be found here: http://www.network-rtk.info/intro/introduction.html or here http://www.precisionmidwest.com/index_files/Page1523.htm
Note that RTK networks are primarily in use today for surveying, but will be moving into agricultural use soon.>
Getting a radio license from the Federal Communications Commission can be daunting, The best way to do it is to use a licensing bureau, and Atlas is a very good company for this. http://www.gpslicense.com
As mentioned on the DVD, there are some cheaper lightbars on the market. One of the most intriguing is this one. I don't know if it's useful, but it's cute. http://www.farmworks.com/hardware/microguide/index.html
Guidance products were originally designed to be "stand-alone" products, but are increasingly a "platform" from which one can build an automatic steering system. Seen in that way, the more capable products like the AutoFarm ATC and the Trimble EZ-Guide 500 may be seen to be much more effective. Even though they're expensive as "stand-alone" guidance products, they provide a much better system when you add steering capability.>
The vendors of sub-inch RTK systems are
Trimble: http://www.autopilotgps.com/
John Deere: http://www.deere.com/en_US/ag/servicesupport/ams/RTK.html
AutoFarm: http://www.autofarmgps.com/products/product.cfm?id=273>
Case: http://www.caseih.com/products/series.aspx?seriesid=2508&navid=105&RL=ENNA
AGCO: http://www.auto-guidenav.com/Agco/AutoGuide/AutoGuideUK/
Sub-inch RTK systems typically cost around $30,000, including the in-cab computer, the GPS receiver, the base station, and the vehicle install kit. Of course, if you already have access to a base station (if you already have a base station or are in an area with an RTK base station network) it will take from $6500 to $16,000 off the price. If you are installing the system on a vehicle that already has a hydraulic steering valve (like a Deere Auto-Trac ready vehicle) you'll save $1,000-$3,000.
Hydraulic DGPS auto-steering products:
Trimble: http://www.autopilotgps.com/home.shtml
AutoFarm: http://www.autofarmgps.com/products/product.cfm?id=274
Raven Precision: http://www.ravenprecision.com/us/Products/productType.jsp?Category=4&Type=1
Outback Guidance: http://www.outbackguidance.com/product/edrivefeatures.asp
(Note: Deere, Case, and AGCO also have systems like these)
Assisted Steering DGPS products:
Trimble: http://www.ez-steer.com/home.shtml
Deere: http://www.deere.com/en_US/ag/servicesupport/ams/AutoTrac-Universal.html
AutoFarm: http://www.autofarmgps.com/products/product.cfm?id=100
Raven: http://www.ravenprecision.com/us/Products/productType.jsp?Category=4&Type=3
Outback Baseline HD: http://www.outbackguidance.com/ordering/viewcatalog.asp?C=7
AutoFarm RighTrac: http://www.autofarmgps.com/products/product.cfm?id=471
Trimble EZ-Guide 252: http://www.trimble.com/aggps_ezguide252.shtml
Links to all the vendors can be found here: https://www.ayrstone.com/GPS_Steering.html
We have tried to provide some general pricing information on the DVD, but it's impossible to get it right because (1) the prices are always changing, (2) the actual price you pay will depend on what options and extras you do, or don't, get, and (3) what you pay depends on how well you work the deal with the vendor or dealer.
Many of the vendors do not publish list prices to the public. Outback is one notable exception: http://www.outbackguidance.com/Ordering/viewcatalog.asp
AgLeader lists most of their prices on the Marten Farms website. Since most of the gear is the same as Trimble's, this serves as a good price check on Trimble's gear: http://www.123farmworks.com/agleader.htm
Similarly, Farmworks publishes a price list for most of Raven's gear under the "Hardware" section here:https://apollo.jtlnet.com/farmwork/ordering/orderframe.html>
One of the most interesting things for RTK and near-RTK systems is the disparity in the prices of the "rover" part of the system and the base station part of the system. Neither AutoFarm nor Trimble publish these prices to the general public, but it's interesting to note that Trimble's prices for the "rover" part of the system (the part on the vehicle) are relatively low, but their base station prices are, usually, over twice what AutoFarm's are. Of course, in reverse, the rover portion of the AutoFarm system is relatively expensive, but the base station is very inexpensive relative to Trimble.
Unfortunately, it's very difficult to make one vendor's base station work with another vendor's rover. There are incompatibilities in the data stream as well as the radio systems that are used to transmit the RTK data to the rover.