November 2008: Cover Story

Mapping Minor

It may seem like a mystical process — gathering info from the sky to work on your terrestrial jobsite, but there’s a method to machine grading mapping. The first and most important step is to convert the 2-D file (the blueprints) into a 3-D digital terrain model. Many grading systems come with software that takes the 2-D model from IOCAD and translates it into 3-D for the model.

In-cab displays alert the contractor to the grade. While some are simple alert displays (like this one), more in-depth systems offer full-color LCD displays.

After you have the digital model, you have to localize the jobsite. This means that you are taking the jobsite and tying its physical position with that of the satellites. This is done by walking around the jobsite and placing the handheld GPS rover for a short amount of time on control points put in by the surveyor. The number of points depends upon the size and layout of the jobsite, but you need to provide at least four.

You then take the file from the rover unit and put it into the GPS control box on the machine to be controlled. Now, the GPS system knows where the machine is on the jobsite and its activity in the programmed job.

“Operators would have access to the data, where to pinpoint the spot they need to be digging at and see the surrounding area — giving them a more complete picture of the job, so they can think beyond just controlling the blade to stay on grade,” says Calvird. “Operators have indications or full automatic control to help them do that, so they can think at a higher level of ‘What’s the best way to do this job?’ and ‘How does this fit in with all the other construction going into this job?’”

Although getting the information to the machine is the primary goal of the rover, it can be used for more than just machine data.

“Just about everyone uses the rover before they start moving material,” says Lodge. “I might go out and do a quick topography before I bid a job, but usually you bid on what the engineer sends out. But before moving any material, I go out and do a good topo of the existing surface and compare it to what the engineer provided. If they match up — great, I’m going to work. But a lot of times you’ll find out the existing ground topo was based on an aerial survey or material has moved in or out and you find that you have an additional 20,000 or 50,000 more yards to move that you didn’t anticipate. You want to make sure you will be compensated before you move the dirt because once you start, it’s pretty hard to get after the fact.”
Beyond the initial bidding, you can also use GPS grading systems to plan beyond the initial stages of the project. For example, an operator might pile material up on a jobsite during a rough grade and then find out in the next phase that the material has to move to another spot. By analyzing the job with the GPS system first and planning the job ahead of time, the operator can move the material to the proper place the first time.

When dialing in your grading work specifications, you can also map the location of known utilities to show on the screen — giving the operator yet another layer of visibility. Being able to mark these utilities on a display that can alert the operator that he or she is digging near an established utility line is more than just a feature — it’s peace of mind

The Vastness of Grading

Not one star in the sky looks the same. Some twinkle brighter than others, while some seem unattainable in the distance, but they come together in a cluster to create an image that is greater than any individual part. Grading systems work in a similar way. While a contractor may start with a simple laser or sonic-based system for finish grading, adding a GPS-based system to the mix is as simple as glancing at another part of the sky when looking for more stars.

Those antennas aren’t for receiving the hottest satellite radio stations. They receive and send positioning data to allow the operator to rock the jobsite with productivity.

For many contractors, it comes down to price when getting into grading systems. A basic flat laser, sonic or site recognition system can range from $5,000 to $15,000 depending on the options such as the display system. GPS, on the other hand, is a larger investment running $30,000 to $55,000, not including the $20,000 base station. The tradeoff is that once the major investment is made, you can add components such as a laser or sonic system at a fraction of the starting cost. And there’s the added value you get out of maximizing your productivity and bid preparation.

“Even though it costs five times as much as a conventional 2-D system, the payback from a 3-D GPS system is five times quicker,” says Lodge. “In reality, everyone is going to have some system or else you’re not going to be able to compete. If you have two contractors bidding the same job and you have one that can increase his productivity 40 to 50 percent or more, then the other guy can’t compete.”

With technology moving at such a rapid pace, new features and options are well stocked. For applications where the GPS equipment cannot pick up signals from the sky, such as inside a building or in a heavy tree canopy, a robotic total station known as a Local Positioning System (LPS) or Theodolite Positioning System (TPS) can be used to send the position information. The robot tracks the machine as it moves and wirelessly sends X, Y and Z data to the control box, letting it know where it is on the jobsite.

For greater jobsite visibility, Leica Geosystems subsidiary Cable Detection Ltd. offers an excavator-mounted utility detection system that alerts the operator when he digs close to metallic, buried utilities. While not exactly a part of a grading system, it can provide the operator with added underground and grade knowledge.

Greater jobsite direction and knowledge is an important edge to have over the competition. With job costs skyrocketing, a system that lets you plan the job ahead of time, conserving fuel, time and money, is well worth the investment. Where generations of old have used star charts for navigation, today’s contractor looks to the sky to chart his own course of productivity and profitability.

Jason Morgan is Associate Editor of Utility Contractor.