Farmers use GPS guided tractors

[Teegate]

Accurate to less than one inch! I need to get one.


http://www.cnn.com/video/#/video/tech/2009/06/13/myers.gps.tractors.cnn



Guy

 

[Boyd]

Accurate to less than one inch! I need to get one.

Well how about the Trimble GeoXH? http://www.trimble.com/geoxh.shtml

Unfortunately it will "only" get you about 3" accuracy. But if you shop around, you might be able to find it on sale for $5,000.

 

[james ungehajer]

Well how about the Trimble GeoXH? http://www.trimble.com/geoxh.shtml

Unfortunately it will "only" get you about 3" accuracy. But if you shop around, you might be able to find it on sale for $5,000.

Wow, i'll stay with my $99 E-Trex, accurate to 13 feet.

Jim

 

[Boyd]

Wow, i'll stay with my $99 E-Trex, accurate to 13 feet.

Not to burst your bubble, but if you look at the specs you will find it is only accurate within 10 meters (33 feet). Stand at a known location and draw a 33 foot radius circle. Now create a waypoint with the GPS. It will fall somewhere inside that circle. Return to the same known location a number of times and repeat this. All the waypoints should be within that circle. HOWEVER, one of them could be at the extreme North end of the circle and another at the extreme South. These points would be 66 feet from each other, and your GPS would still be operating within its specs. If you repeat this process a lot of times and average all of the waypoints, it should be very close to the center of the circle. But individual readings can be quite different from day to day.

This is pretty much the same for all consumer grade GPS'es. The "13 feet" reading you see on the satellite page is just an approximation which may be useful for comparison (a 13 ft reading is better than at 42 ft reading for example). But it isn't an absolute quantity telling you that your unit is accurate to within 13 feet.

Nevertheless, this is usually "good enough" for the kinds of things we do, and unless you want to spend thousands for a unit like the one above, it is typical for any of the consumer models you can buy.

I really don't know much about surveying - maybe Scott can enlighten us - but as I understand it, you can use portable GPS "beacons" placed at known locations to get highly accurate readings. I suspect that may be how they achieve the 1 inch accuracy that Guy mentions.

 

[james ungehajer]

Boyd

The time i looked for the Geodetic at Four Mile Circle i lucked out, their was a surveyor there and he was using the portable GPS Beacon that you talked about.

Guy's coordinates are my nirvana.

Jim

 

[46er]

I really don't know much about surveying - maybe Scott can enlighten us - but as I understand it, you can use portable GPS "beacons" placed at known locations to get highly accurate readings. I suspect that may be how they achieve the 1 inch accuracy that Guy mentions.

In Yellowstone they use GPS, among other things, to keep track of earthquake and ground movement as part of the volcanic monitoring. The USGS has beacons stations like the one below through out the backcountry. They need centimeter accuracy, not sure what they use.

 

[DeepXplor]

GPS and tractors

Accurate to less than one inch! I need to get one.


http://www.cnn.com/video/#/video/tech/2009/06/13/myers.gps.tractors.cnn



Guy

Brazil has been using GPS guided tractors for at least three years. They claim to be accurate to within an inch or two. The farms that they use them on are 20,000 acres, or in that area, much larger than what we see in the US. They run them day and night because the GPS doesn't care what time it is. They need somone on board the tractor because of when to stop and turn for the next row. The tractors have a 30ft swath. They use mostly Cats and GPS systems from the US. Their fertilizer comes from US and Canada.

 

[Boyd]

The National Geodetic Survey also operates a network of GPS base stations which are used to provide more accurate readings. Check out their site and the interactive map showing station locations:

http://www.ngs.noaa.gov/CORS/

The National Geodetic Survey (NGS), an office of NOAA's National Ocean Service, coordinates a network of continuously operating reference stations (CORS). Each CORS site provides Global Navigation Satellite System (GNSS - GPS and GLONASS) carrier phase and code range measurements in support of 3-dimensional positioning activities throughout the United States and its territories.

Surveyors, GIS/LIS professionals, engineers, scientists, and others can apply CORS data to position points at which GNNS data have been collected. The CORS system enables positioning accuracies that approach a few centimeters relative to the National Spatial Reference System, both horizontally and vertically.

New Jersey also operates a station in Trenton - see:

http://www.state.nj.us/dep/gis/faqgps.htm

Under normal circumstances a GPS receiver should be able to determine a fix for a user's location to within 10 meters. Very often, the results are in the 5 to 7 meter range. To consistently achieve better than 5 meter accuracy, GPS measurements from a base station are needed to differentially correct GPS measurements determined in the field.

Several sources of error related to timing, satellite orbits, and the atmosphere affect GPS measurements. The GPS measurements collected by a base station are used to model these error sources at any given time. Since the measurements at the base station are collected at a known location, these sources of error can be determined and used for improving or correcting field data that was/is collected at the same time.

The differential correction can be performed on field data after the data has been downloaded to a PC running GPS data processing software (post-process correction), or performed in real time while the field data is being collected. Generally the post-process correction solution is more accurate, and is favored over the real time solution when requirements dictate achieving higher accuracy. Real time correction still typically provides better than 5 meter accuracy, but users might not always be able to receive the correction signals in all environments. Naturally, the real time solution has advantages when using GPS for navigation.

Base stations are ground based, and collect and store GPS measurements for later retrieval by users. Some base stations also transmit correction data that are used for real time differential GPS. Many newer GPS receivers have WAAS (Wide Area Augmentation System) correction capabilities. WAAS is a satellite based real time correction solution that was initially designed to aid aircraft navigation.