When does a design model become a GIS model?

October 2011 » Columns » CE + GIS INTERSECT
Janet Jackson, GISP

Civil engineer perspective
Kahler: Most modern infrastructure design is done in an electronic environment, with 2D and 3D files representing the model of the project that the design engineer intends to have built. This design model, sometimes known as master files, consists primarily of basic geometric elements such as lines, arcs, spirals, and even parabolas for vertical curves. These elements constitute a graphical requirement for the project and are intended to be combined with specifications that provide the tolerances and materials. At some point, however, the project is actually built and becomes part of the landscape. The question that many are asking is: Should the project continue to be represented by its theoretical design model, or should its actual finished condition be represented by a technology that was designed to manage information about the existing world – in this case, GIS?

GIS has evolved to deal with existing, incomplete information. While the as-constructed condition of the project can be measured at discrete locations, it is impractical to measure every feature of the project, especially those you can't see or touch once they are in place. Measuring the project is practical, just not in the pure original geometry of the original design file. You can't really measure the true constructed center of a large horizontal curve, or the true tangent points, but that's how these elements are stored in the original design. So keeping actual measurements in GIS is more practical because it doesn't assume anything that you didn't actually measure.

Many design errors have resulted from an assumption that an element was built exactly as designed when it really wasn't. GIS has better capability to store information about the inspections, samples, and tests that were performed on the project than the typical design platform. These inspections, samples, and tests are necessary to confirm that the project was built according to the plans and specifications; some states require that this information be completed before accepting the work.

GIS can serve as a complementary platform to design tools, capturing and managing all measurable characteristics of a constructed project to support project management, final acceptance, operations, and maintenance. The challenge for implementation is in defining an information model for constructed projects that is practical, yet still contains enough information to answer our key questions about the project.

Danny L. Kahler, P.E., is a civil engineer with more than 25 years of experience in transportation design and construction. He developed a new technology-founded engineering practice method known as Model-Centric Quality Assurance. Learn more about Kahler Engineering Group at www.kahlerengineering.com.

 


GIS perspective
Jackson: A common saying I have is, "The technology has already been invented to solve many problems. What has not been invented is the people who will use the technology." With that in mind, I believe a design model becomes a GIS model whenever the personnel on the project are ready to make the case that a central repository, such as GIS, provides the right technology for storing, organizing, and displaying all the project pieces and parts.

Danny Kahler is correct when he says that "the challenge for implementation is in defining an information model for constructed projects that is practical, yet still contains enough information to answer our key questions." However, the challenge can be solved. I suggest the engineer and a GIS professional sit down together and work out the basic GIS database structure needed to house all of the project's specific information. Project questions to be answered might be: Will there need to be a separate data field for as-built or construction photos? Will the construction photos be date/time stamped or will the data field need to contain this information? Will all the project's inspection reports be contained within the project phases or will they be kept in one project data field? What column heading will be given to the field that contains the reports?

Your GIS database can be as detailed or as general as needed, yet to be useful and efficient, it needs to answer the engineer's questions by visually displaying the answers. If you start with the KISS (Keep It Super Simple) principle, you can add more complex data fields to the GIS data model as you involve more complex engineering projects. Then through a series of trial and error with changes to the GIS database, it will become clear which details of the data model work best for certain types of engineering projects. Again, the GIS technology and data model are flexible and scalable, and there are a variety of online tutorials that can help you get started. Hopefully the next time you find yourself struggling to keep your entire project's pieces and parts compiled, you'll think geospatially and use GIS as your model.

Janet Jackson, GISP, is president of INTERSECT (www.intersectgis.com), a GIS consulting firm. She travels the country talking about the importance of intersecting GIS with other professions to create effective solutions for clients. She can be contacted at jjackson@intersectgis.com.


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