What is GPS?

The Global Positioning System (GPS) is a highly accurate satellite-based radio-navigation system providing three-dimensional positioning, velocity, and time information. GPS is an all-weather system that provides continuous worldwide coverage.

How is GPS used?

GPS receives signal from four or more satellites in view to calculate position, velocity, time, and other data as needed for precision construction applications. In construction, the position data is collected and used with site design files to provide cut/fill and horizontal positioning information to the operator.

How accurate is GPS?

  • A single mobile GPS receiver operating in autonomous mode is accurate to about 10 m (10 yards).
  • If you supply the GPS receiver with corrections derived from a GPS base station within about 300 km (200 miles), known as differential GPS, the accuracy improves to better than 1m (3 ft).
  • If you use a GPS receiver with more processing power and transmit data in real-time from a base station within 20 km (13 miles), known as real-time kinematic (RTK) GPS the accuracy is 10-30 mm, or better than 0.1 ft.


Where can you use GPS?

GPS is a worldwide, 24-hours-a-day positioning system. GPS requires a clear view of the sky and works best in open areas. To initialize, an RTK GPS unit requires at least five satellites. After the initialization, an accurate position can be computed with a minimum of four satellites.

What is AccuGrade GPS?

AccuGrade GPS is a family of products for machine grade control, designed specifically for earthmoving equipment in the construction industry. Trimble is the #1 GPS provider in the world. Caterpillar and Trimble setup a partnership to provide GPS solutions for contractors. After creating the partnership, they created the AccuGrade product line.

Trimble and AccuGrade are essentially the same products. AccuGrade machine control systems are built for ARO machines. ARO stands for AccuGrade ready option, meaning the machines are pre-wired from the factory ready to accept Laser & GPS equipment. Caterpillar is building their machines ARO ready right on the assembly line.

AccuGrade GPS is available for dozers, motorgraders, & excavators. Trimble systems are available on scrapers. It uses satellite positioning to provide blade guidance to the operator, or to automatically control the blade hydraulically.

For dozers and graders, AccuGrade GPS provides up/down and cross slope blade guidance as well as left/right direction to the operator using lightbars and an on-board color display. For scrapers, GPS provides up/down cutting-edge guidance with a single lightbar. The system includes a GPS receiver, a single GPS antenna and mast, and an on-board color display.

What are the benefits of Caterpillar partnering with Trimble?

  • Trimble is the #1 GPS provider in the world.
  • Trimble patented the dual mast system, which reads off of both corners of the blade, providing customers with fast & efficient real-time cuts and fills.
    • This helps customers in various situations, such as seamlessly cutting a super elevated curve, or putting systems on finish dozers with 6-way blades. Other systems do not have rotation sensors on the 6-way blades, making it a guessing game when you are cutting slopes or super elevations.


What is the difference between a Base Station, Rover, and a Machine System?

  • A Base Station takes satellite signals & translates the corrections to the job’s specific Northing, Easting & Elevation. Every jobsite needs a Base Station. Rovers & Machine Systems cannot operate without receiving radio signals from a Base Station.
  • A Rover is a jobsite management tool. With this tool, you can look at your jobsite plans, setup a jobsite, perform stakeouts, follow alignments, topo stockpiles & calculate quantities.
  • A Machine System consists of two GPS Receivers, masts, a radio, and a display box. The display box, mounted inside the cab, has a set of plans on the screen. This enables to see where the machine is relative to the jobsite at all times. You can see cross-sections, calculate vertical and horizontal offsets and automatically finish grade any road or site. Yes, the dozers and motorgraders have automatics!


What are automatic controls?

An optional automatic control kit provides direct input to the hydraulic valves to control the lift and cross slope of the dozer blade. The operator can drive anywhere on the job site and with the flick of a switch easily connect the machine’s hydraulic system to the GPS receiver and the design data to position the blade automatically.

By automating the final passes, operators can get complex jobs done faster than ever. Automating the blade control reduces site preparation time, minimizes operator fatigue and lowers operating costs, while giving you a consistently higher degree of accuracy.

Does AccuGrade GPS require a GPS base station?

To achieve stated specification for RTK GPS, it is necessary to use a Trimble RTK base station as part of the AccuGrade GPS setup.

Can I use AccuGrade GPS with any Trimble GPS base station?

AccuGrade GPS is compatible with any Trimble RTK base stations as long a suitable 900 mhz data radio is used. Site Vision Base Stations & SPS Site Positioning Base are compatible with AccuGrade GPS. In other words, if you have purchased a GPS Base Station newer than 2002, you won’t have a compatibility problem.

How many GPS base stations do I need?

A single base station can support any number of machines within approximately 20 km (13 miles) of the work area. In order for this to happen, there must be uninterrupted radio communications between the base station and the machines. For best results, the base station is typically located on the construction site.

Can I use AccuGrade GPS on any type of machine?

AccuGrade GPS configurations are currently available for dozers, motorgraders, excavators, and scrapers. Caterpillar & Trimble have thoroughly tested AccuGrade GPS operating on these types of machines. Other machine types will be supported in future releases.

How does AccuGrade GPS compute cut or fill?

AccuGrade GPS requires a digital site design (a digital terrain model or road design) in the on-board display. Using the GPS blade position and the blade cross slope, the ground elevation at the base of the blade is compared to the design elevation. The difference between the two elevations is the cut or the fill.

Why does AccuGrade GPS use three lightbars for guidance?

The lightbars provide 3D guidance to the operator. One of the lightbars is mounted horizontally in the center of the cab. Lights flash to indicate left or right, guiding the operator along a defined alignment. This alignment may be a road centerline, or edge of road, or any other line of interest.

The other two lightbars are mounted vertically and correspond to the right and left edges of the blade. Based on an input design file, cut or fill is computed for the base of the blade, and the lightbars direct the operator to raise or lower each side of the blade accordingly.

What files can be used on the data card?

Several types of files are used by AccuGrade GPS:

  • Design (Place, DTM (grid of TIN) or road alignment) – used to compute cut/fill throughout project area
  • Background DXF – used for viewing perimeters and avoidance zones (optional)
  • GPS Calibration – used to convert GPS positions to local site coordinates
  • Machine settings – includes blade width, antenna height and offsets above base of blade