Feature: Moving to Machine Control
Professional Surveyor Magazine - November 2010
The owner of a data-management company describes five skill sets surveyors need for 3D data preparation.
By Thad Glankler, PE
I started working for a machine control dealer eight years ago, managing their construction data services division. Today I run my own data-management company. Over the past eight years the two questions I’ve heard asked most frequently by engineers and surveyors about machine control are “What do I need to know to create models for machine control?” and “How do I make money with it?”
I believe these are both related to the underlying (unasked) questions: “How can I replace my lost income due to the lack of construction staking with the widespread use of machine control?” and “What experience do I need so I can provide complete data management?”
I have identified five different skill sets that a good 3D data manager or management company should possess. To illustrate them I describe below a typical data-management process for a project. These different areas of expertise overlap during the data-management process, and the importance of one area isn’t any greater than another. On different projects one area of expertise may be used more frequently, depending on the nature of the project.
The areas of expertise that I have identified, in no particular order, are CAD; applying surveying, engineering, and construction staking knowledge in new ways; and learning about machine control.
Learn to Work with CAD Files
Obviously, one possible new source of income is preparing 3D data models for a construction project that uses machine control or a GPS rover. These models are usually produced with CAD files and paper plans. Although I have created models entirely from paper plans, the CAD file is typically available after the project has been awarded, and then you can incorporate that data into the 3D model.
The design CAD file can be delivered in a variety of file formats, and a good CAD operator should be able to identify the different file types and use them accordingly. Some of the file types you may need to be familiar with are .dgn, .dwg, .dxf, .pro, .ttm, .tin, .aln, .svd, .svl, .tn3, .tp3, and .xml. I have imported design files with as few as 30 layers to over 300 layers (Figures 1 & 2
). Being able to identify the layers you need and use them efficiently is paramount to getting started. Knowing how to evaluate the design layers, xrefs, viewports, paper s
pace/model space, drawing scales, and the overall drawing validity for 3D modeling goes a long way in helping produce an accurate 3D model.
I have prepared hundreds of models from CAD files, and all of them have needed some “cleanup” of the CAD drawing before I could start to build the model. You need to use your surveying knowledge to ask yourself some important questions about the CAD file.
• Is this the correct file, and does it match the paper plans?
• Are there phases?
• Do contours have elevations, and if so, are they the correct elevations?
• Are pavements and curb lines continuous lines or are they broken?
• Are curb lines 3D sloping lines or flat?
• Are spot elevations real “points” or just text representing spots?
• Is the project in the correct coordinate location, at the correct scale, and in the correct units?
• Do building pads have elevations or are they flat?
• Is there road profile information, horizontal, vertical, or superelevation already defined so as to save some time?
Apply Your Surveying, Engineering, Construction Staking Knowledge
After the initial cleanup, the 3D modeling can start. If there are both defined roads (horizontal and vertical profiles) and typical sections, the typical sections are applied and any superelevations and widenings are added to the model. Having the engineering knowledge of how roads are defined (horizontal and vertical alignment and superelevation) allows you to recognize if there are any missing or incorrect data. Once errors are identified you can correct them, or, if they require a major design change, bring them to the attention of the design engineer to correct. All road intersections should be transitioned smoothly from radius point to radius point and from the edge of pavement to at least the right of way.
In building a model, there will be many areas where an elevation is needed and not specified, such as high/low points, spot elevations on curbs, and elevations around buildings. Your engineering and construction staking experience helps in identifying these areas and creating a workable model.
The contractor will need the site to be “calibrated,” and this calibration file must be added to the 3D surface file and associated linework files for the equipment to grade the site correctly. The best practice is to have at least five control points (northing, easting, and elevation) spread evenly around the perimeter of the project, which will be used by the contractor to translate and rotate GNSS measurements to the site coordinate system. Setting these points, calibrating the site for the contractor, and creating its associated calibration file are possible income sources for surveyors in situations where the contractor is creating the 3D model.
If the contractor needs additional information, such as 3D underground utility line data for trenching, you should collect existing ground points after the site has been cleared, compare the existing contours to the plan topography, and prepare a report or plan to show the discrepancies (Figure 3
). It is better for the contractor to know if his or her earthwork quantities are correct at the start of a project, rather than at the end.
Progress quantities can be determined by collecting topographic data at predetermined intervals and then creating maps (plan, profile, cross-sections) to show the changes and earthwork quantities (Figure 4
). Material quantities zcan also be established by the same method after the subgrade is cut. After the base is graded, collect the top of base points and generate your volume. The contractor can compare your number with his truck count and use this information for bidding future projects. This process can be repeated for all layers of materials.
Computing stockpile quantities is another potential source of income related to building 3D data models. When contractors need accurate numbers for stockpiles, you can measure the piles with topo points and then compare them against the existing or proposed surface, analyze the data for the quantities, and relay this information to the contractor so he can better manage his projects. You can also verify that detention basins meet specifications by collecting points and generating reports and plans during construction, saving costly regrading after the ponds are constructed and as-built. Like they say, a picture is worth a thousand words.
When building models, you should always have your engineering hat on to look for errors, design flaws, and omissions.
• Is the accessible parking sloped correctly?
• Are the spot elevations correct and phase transitions smooth?
• Are road intersections connected smoothly with no low spots?
Do the details match the drawn contours for roads and detention basins, and do the curb and gutter details match the CAD file?
All these problems will affect the overall constructability of the project. As you go through the entire site, you will find areas that lack in design information, and those discrepancies must be resolved and remodeled.
Some contractors like parking lot islands and medians to be left out of the model so they are able to grade through them without the machines “jumping” when they get to the curbs, but only if the pavement is at a smooth slope, without a major grade break. Landings and steps outside truck docks usually do not get modeled either, because contractors like to grade through those areas as well (Figure 5
). Unless a contractor is doing his own s
taking, accessible ramps in sidewalks will not be needed in the model. You need to check with each contractor to verify how his field crews would like those areas modeled.
One aspect that often gets overlooked in the modeling process is the linework files. A surface is not very helpful without an associated linework file so the operator can see his position (Figure 6
). If the contractor is going to do any kind of staking or alignment checks (centerlines, curb and gutter, storm, sewer, water, etc.), the linework must be adjusted so it can be used based on each equipment manufacturers’ specifications. You need to learn how to handle both the hardware and software differences among vendors.
Learn Machine Control Processes and Procedures
A proficient 3D data manager will need to understand the individual machine control equipment processes. Each manufacturer has its own software to import surface and linework data and create its own unique working files. The process is also different for each manufacturer, so obtaining the individual software packages to create these files is important. If you get a call from the field saying that the contractor thinks there is a problem with the model, you’ll need the skills to troubleshoot their equipment with them to determine if the errors is with the model, equipment, or operator.
I have found that most errors are related to field procedures, so a data-prep firm should offer to periodically check the contractor’s field procedures and help train the field personnel in proper procedures, maintenance, daily setup, blade-wear check, rover checks, machine checks, offsets (vertically and horizontally), grade checking, point collecting, and construction staking.
To gain the experience necessary to offer machine-control-related services, you can contact your local machine control dealers for training in correct model-building techniques, or better yet contact a contractor who uses machine control to set up a duel training day or two—and offer to share the cost. Familiarize yourself with all the equipment you will be providing data for and ensure that the data is created so as to maximize the efficiency of each unique piece of equipment.
You can also gain valuable insight by searching the internet for data-prep providers and viewing examples of models they have created to see how models are being built and used in your area. Learn everything you can before submitting your first proposal to build a model for a contractor. Remember the old saying, “You get only one chance to make a first impression.”
Thad Glankler, PE is the president, founder and owner of Glankler Data Services, LLP, a data-prep management company that specializes in data prep for GPS machine control throughout the United States. Mr. Glankler is a registered as a professional engineer in North Carolina.
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