GPS guidance system (agricultural)

01

Choose the accuracy and correction service

The US government's GPS.gov agriculture page explains that combining GPS with geographic information systems allows precise farming: receivers map field boundaries, roads, irrigation and problem areas, and guide farmers back to the same locations year after year. It lists benefits including accurate field navigation that minimises redundant applications and skipped areas, maximum ground coverage in the shortest time, the ability to work in rain, dust, fog and darkness, and the elimination of human flaggers for spraying. [1]

Hemisphere GNSS, a receiver maker, describes its Atlas L-band correction service as delivering accuracies from sub-metre to sub-decimetre, with a basic tier giving SBAS-equivalent performance where Atlas is available and a feature that lets the receiver re-converge quickly after a pause. [2]

Kansas State University's extension guide MF2942 (2011) groups agricultural guidance by correction type. It gives WAAS (SBAS), which is free, an accuracy of 12 to 15 inches or better, with year-to-year accuracy varying by as much as 6 to 15 feet. For OmniSTAR subscription services it lists VBS at sub-metre, XP at 6 to 8 inches pass-to-pass and HP at 4 to 6 inches pass-to-pass, at $800 to $1,500 a year. RTK systems have antenna accuracy in the ±1 inch range, but tractor steering and vehicle dynamics can widen this to 4 to 6 inches. They need a base station less than 30 miles from the rover and a radio link: either a local base subscription at $750 to $1,500 a year, or a portable base at $5,000 to $15,000 within 3 to 5 miles line-of-sight. [3]

CHC Navigation's NX510 Pro data sheet (revision July 2022) is one current RTK example. It specifies RTK accuracy of 8 mm + 1 ppm RMS horizontal and 15 mm + 1 ppm RMS vertical, initialisation in under 10 s with over 99.9% reliability, and pass-to-pass accuracy of ≤ ±2.5 cm. It tracks GPS, GLONASS, Galileo, BeiDou and QZSS plus L-band RTX corrections, and accepts CMR, CMR+, RTCM 2.x and RTCM 3.x through an integrated 4G modem or an external radio. [4]

Editorial calculation: if a 12 m sprayer overlaps the previous pass by an average of 0.5 m, about 0.5 / 12 ≈ 4.2% of the field is treated twice; halving the overlap to 0.25 m halves that to about 2.1%. Boom width and overlap are assumed examples; ask the supplier for pass-to-pass accuracy figures for each correction level.

Kansas State recommends setting the guidance overlap to match the correction type: 3 to 4 inches less than full toolbar width for RTK, 4 to 6 inches for OmniSTAR and 12 to 15 inches for WAAS. Setting it below the available accuracy reduces field efficiency. [3]

Give the supplier the operations (tillage, planting, spraying, harvesting), implement widths, required pass-to-pass accuracy, correction service preferred (satellite, RTK base or network), tractor make, model and steering type (assisted wheel or integrated hydraulic), display and ISOBUS needs, section control, field size and terrain, and support and subscription terms.

02

Connect the steering and implements

Hemisphere describes building agricultural guidance and control systems from single-box auto-steering solutions with ISOBUS virtual terminal (VT) client support and definable CAN and serial messaging, smart antennas to improve guidance terminal accuracy, and custom integrated application interfaces. [2]

The CHC NX510 Pro steers through an electric steering wheel rated at 7.5 N·m torque with a 410 mm wheel. It has two CAN ports, two RS232 ports, ISOBUS compatibility, a 10.1-inch IP65 touch display, a receiver rated IP67, a 9 to 36 V DC supply and an operating range of −20 to +70 °C. Its GNSS+INS terrain compensation is said to keep hands-free driving accuracy within sub-inch. [4]

Kansas State notes that vehicle roll, which can be 5 degrees or more, can offset ground coordinates by 3 to 12 inches. Hilly and contour guidance should use a tilt sensor, and inertial units allow 10 or more minutes of guidance without satellites, which matters for RTK units that can need 10 to 15 minutes to re-initialise after signal loss near tree lines. [3]

Editorial note: confirm whether the kit steers through a motor on the steering wheel or the tractor's hydraulics, which ISOBUS functions the display supports with your implements, and how corrections are received and paid for.

Editorial calculation: a 5 degree roll moves a cab-roof antenna sideways by about h × sin 5° ≈ 0.087 × h, so an antenna 3 m above ground shifts about 0.26 m (about 10 inches), which is within the 3 to 12 inch range Kansas State gives. The 3 m height is an assumed example. [3]

03

Compare system types

No manufacturer record linked to this page has been confirmed. The types below come from the sources reviewed.

Kansas State divides systems by correction type and output. A basic WAAS light bar has the lowest cost and an auto-steer RTK unit the highest. Its chart lists WAAS as suitable for spraying, planting wheat and general tillage, and RTK for strip tillage, second-pass banding of fertiliser and 2-inch cultivating. [3]

Makers sell the hardware in different packages. Hemisphere offers receivers and smart antennas that feed a guidance display, single-box auto-steering controllers with ISOBUS and CAN interfaces, and correction services at sub-metre to sub-decimetre accuracy. [2] CHC's NX510 Pro packages an electric steering wheel, receiver and 10.1-inch display as a retrofit kit that can be moved between tractors. [4]

04

Trace the system components

This is a functional reference built from the sources cited; it is not one maker's specification.

05

Fill the specification fields with values for your farm

A guidance system quotation needs values for your farm. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the operations, tractor and accuracy data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Operations: [tillage; planting; spraying; harvest]
Implements: [widths; ISOBUS]
Accuracy: [pass-to-pass target]
Corrections: [satellite; RTK; network]
Tractor: [make; model; steering type]
Support: [installation; subscription; training]

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