As we get more classes filled for training, I seem to get one question that confuses potential students. “Why do I need a class in both Data and Takeoffs?” The two disciplines are related, but in practice are very different. I will  breakdown some of the differences.

Surfaces:
Sure, takeoffs require two surfaces and data usually only one. Existing and proposed information may be in one or all of the three basic elevation elements. Points, 2D lines (contours) or 3D lines (curb or breaklines).

It is how these surfaces are prepared and detailed that makes the difference. In a takeoff often times the best you can do is to review the existing surface for vertical spikes and use the supplied data. The best thing is to perform a topo of the site and use it for accurate results. There are two problems with this. First your number may be substantially different than everybody else’s. Second if there is no information to localize your GPS to the site it is hard to fit a topo from assumed coordinates into the takeoff. Takeoff training addresses these and other issues, data builders won’t use this much.

The surface necessary for use in machine control and layout goes through more checks and fixes than one for a takeoff. When we do a takeoff for a client, and then are asked to do the data, we start all over again. The process for a data surface is so completely different than one for a takeoff; the approach varies from the initial opening of the file. Data builders need to use different steps in building their surfaces.

Subgrades:
During a takeoff there may be areas where the subgrade depth is not called out. An educated guess will be made and life goes on. Data needs an Request For Information to get the correct depth. For data, the easiest way to do subgrades is to draw 2D lines and dial down the finish to the appropriate depth. To get accurate dirt quantities subgrade depth and type of material go a long way in getting the best results possible. Data folks don’t worry much about subgrades, takeoff needs plenty of detail.

70% of our takeoff students are not sure what to do with shrink and swell. Some software needs the amounts entered differently to make it work. It is sometimes difficult to make educated guesses at the exact percentages unless you just finished a job next to the proposed site. In training we get everybody comfortable with it, data classes don’t talk about it.

Bore logs can make a job profitable or go upside down quickly. Takeoff training goes into great detail about how to deal with bore logs and what to do when they are not dense enough. Topsoil stripping and replacement gets confusing. Takeoff must be accurate in the amounts of material available and what is to get used and what can get sold off the site. The whole issue of sub-surface strata is critical in a takeoff. Data gets involved when the crew hits rock where there was not supposed to be any. Dealing with those issues is a takeoff function, but quite easy to learn and a good tool to have for data professionals.

Linework:
In a takeoff, the linework for subgrade areas needs to be correct so the program reduces the correct areas. The best example of this is for islands, you don’t want the paving in those areas. When building data, this linework cannot be used, if you were to try and follow a “donut hole” section it would drive an operator crazy.

These are several of the differences in what education is required for takeoffs and data. Our courses are targeted to these and other disciplines. At some point in the future, I will talk about the differences in sites and roads.