Even with 3D machine control systems on site, there still remains a need for construction layout.  If you employ machine control, the number of stakes and check shots will definitely be decreased but some layout will still be needed. So what are the options and what capabilities are available with today’s modern layout systems?

Current equipment options range from the tried-and-true automatic level, theodolites and string lines to the more modern laser levels, total stations and RTK systems. Techniques vary from turning lots of right angles and simple grade determination to radial stake out and beyond.  Depending on the equipment used, manpower requirements vary from a one-person layout crew to the traditional 2-3 member teams. In this article I would like to address the most advanced, modern techniques that save time and money while increasing accuracy and convenience at the same time.

The engine of the advanced techniques is the on-board or handheld field computer.  These devices are also known as “field controllers” or “data collectors”.  They have incredible computational power and user-friendly interfaces that include graphics and loads of information for error checking.   Whether connected to an optical total station or a RTK GNSS (GPS) system they deliver fast and more accurate results.  At the same time they provide lots of options to get the job done faster and more flexibility for getting the job done right.  Following are some examples of the different possibilities as they relate to construction layout and data collection:

Layout by coordinates:
This technique allows placement of the total station in any location convenient to the area where the layout is to be performed. The total station can be placed over a known control point and oriented via a traditional backsight point or placed in a more convenient location and oriented by measuring to two, or more, other control points.  Once the total station’s position is established and oriented, the field controller guides the users to the desired layout point.  At that time cut and fill information is displayed.   Offsets to the point can be set in similar fashion.  The user interface for navigation to the layout point can be graphical or numeric-only, but either method is very fast and efficient. Using an RTK system for the same task removes the need for backsight or reference points and eliminates the need for ground-level line of sight.  Whether optical total stations or RTK is used, the need for measuring tapes and right angle measurements is eliminated. This technique is referred to as “radial stakeout” by surveyors and has been their bread-and-butter method since the invention of the total station and data collector.

Layout to a reference line:
In this technique all points are referenced to a pre-determined, or field-measured, line.  It could be a building line, curb line, straight section of a centerline or any other line on the plans.  Positions are indicated as a distance down the line (from its starting point) and offset right or left.  You could also think of this as station and offset measurements.  This technique eliminates the need to calculate coordinates before hand and is great for as-built checks. When laying out points using this technique, the navigational guidance to the point is similar to that provided when laying out by coordinates, either graphical or numeric-only.  It is a very efficient technique for laying out batter boards or anything you can reference to a line on the plans.  The total station need not be positioned on the reference line for this method to work, thus eliminating line-of-site issues. Of course, the same is true using an RTK system.

Layout relative to a roadway centerline:
This is very similar to laying out to a reference line, but with more complex alignments. Using this technique, data about the reference alignment is preloaded into the field controller.  This will include straight and curved components of the alignment, super-elevation data and typical design cross section information.  Once this information is loaded and checked, layout can begin with all positions indicated by their station and offset position.  With the typical cross section information and super elevation information loaded into the controller, cuts and fills will be calculated anywhere inside the roadway.  This is also a good solution for ditches and canals or any other complex three dimensional alignment.  As for instrument position, the same options are available as in the techniques mentioned above. One of the advantages of this technique is that offsets can be changed on-the-fly, without the need to re-calculate coordinates.  It is also very useful for as-built applications along complex alignments.

Layout relative to a DTM:
This is a fantastic technique that utilizes the Digital Terrain Model (DTM).  This will probably be the same model that is used in the 3D machine control files.   You can layout any point that is within the model and get cut and fill information immediately.  This is a great time saver for grade checking or when dealing with very complex surfaces such as landfill cells. The field controller/data collector’s computer keeps track of the elevations anywhere on the surface of the DTM, so no reference alignments are required.  If you can get to the point, you can lay it out and grade it.

Layout in a building grid:
New layout controllers expedite laying anchor bolts or any other point inside a building gridline system. The building gridlines can be entered into the controller via a CAD file or hand-entered via the traditional up-and-over dimensions of the building plans.  Once this is done, any point (or offset point) can be laid out using radial stakeout techniques. This means you can place the total station anywhere you can see the layout point and avoid the many line-of-sight issues that are present on a crowded building site.  This is obviously not a good application for RTK systems as the line-of-sight to the sky will most often be blocked by the structure.

Summary:
The capabilities of the modern field controller/data collector are expanding all the time.  Feedback from the field has led to most of these advancements.  The solutions they provide are practical and user-friendly.  The addition of bright, easy-to-read graphical displays and graphical interfaces have greatly improved the user-interface and make for a much- shorter learning curve.

Just as machine control has revolutionized the productivity and accuracy of earthmoving and paving activities, the advancement of these modern layout instruments and techniques have advanced and improved layout work.  Their ability to set points quickly and accurately has forever changed the productivity of layout crews and in many cases reduced the size of the crew as well.  RTK systems, robotic total stations, new advanced laser-based instruments have all had their impact.  Investigation into these new tools and techniques can impact your bottom line as well.

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