One of the most common questions I am asked at seminars is about the issue of liability for land surveyors that are involved in machine control set up and 3D model preparation.  Many land surveyors are very concerned about the potential liability issues that could arise from mistakes on a site calibration or localization, or building a 3D model incorrectly. 

Back in October of 2009, I briefly mentioned the liability issues as it pertains to properly charging for creating a machine control 3D model, but this month I wanted to dig a little deeper into liability issue.  Land surveyors should be concerned about liability, but should this concern keep land surveyors from performing site calibrations or preparing 3D models?  With proper training, systems checks and due diligence, the liability issue should not keep you from being involved with machine control.  This is an opportunity if you approach it correctly.  

I have talked with some land surveyors that don’t want anything to do with machine control set up or creating 3D models because they are concerned with the liability that comes with performing these tasks.  However, in many cases, these are the same land surveyors that have been performing construction layout for years and have no concerns about pounding stakes into the ground and marking them with cuts and fills.  The reason they see liability issues associated with machine control and 3D models may be their uncertainty due to lack of knowledge and experience with the technology.

I have yet to see any situation or reason to assume that there is more liability associated with machine control set up and 3D modeling than there is in normal construction layout.  In fact, I will argue that with proper setup, proper file creation and proper system checks, using machine control and a 3D file will actually decrease the chances of an error and therefore decrease the liability you take on for a project. 

When I have talked to land surveyors about liability issues as they relate to machine control and 3D models, the liability issue is almost always about the liability involved with the 3D model or the vertical element and not the site calibration or the horizontal element, even though site calibrations do incorporate the project elevations.  I think this is because we are naturally used to working with control and elevations and the idea of doing site calibrations is not as threatening to us as working with the unknown 3D models.  However, when I work on a project, I certainly want to limit my liability in both the vertical and horizontal components.  If a project is off vertically by a foot, is that more critical than and being off horizontally by a foot?  It depends on the project, but I believe in most cases, land surveyors are more concerned with 3D files being wrong in the vertical aspect as opposed to horizontally.

On a typical project, if you do a site calibration or localization and tie into the project control correctly and you thoroughly review your calibration or localization file and determine your residual errors are within tolerance, your site calibration and all layout or measurements performed inside of the control points should be within tolerance.  But how do you ensure this from a liability standpoint?  You check, check and recheck.  After completing a site calibration, I don’t just go back and check into a couple of control points and assume the rest are all fine.  I make sure I recheck all control points on the project.  This is a simple way to ensure that all the control points on the project are correct, the site calibration or localization is correct, and all control is within acceptable tolerances.  This is a perfect opportunity for land surveyors to showcase their expertise and value as it relates to this emerging technology!

I also make sure that when we are working on a project, we check into the control points at the beginning of the day, at lunch, at the end of the day, and before and after completing certain tasks.  If you do this, you can virtually eliminate any errors or liability that is the result of bad instrument setups or errors in height or rod measurements.  If you repeatedly check into your control and achieve good results, you can safely assume you are minimizing your errors as it relates to project control. 

Another way I limit my liability on site calibrations is I personally perform the calibration or I at least work along side of my clients as they perform the calibration and we always perform the calibration using the client’s equipment.  By being on site, I can ensure the calibration is done properly and using the proper procedures.  I also like to use the client’s equipment rather than using my equipment and then transferring the files to client’s data collector.  This is just one of those simple measures that gives me a certain comfort level.  If I am using the client’s equipment, there are no chances of transferring the wrong files or not getting the information into the correct location.  I have had too many issues arise when transferring data from one data collector to another or dealing with someone that does not understand the importance of where the files need to be stored in order to work properly.  To me, it simply eliminates the possibility of errors associated with that one step and therefore decreases my liability. 

One of the biggest advantages in creating a 3D file for machine control is that when you take 2D paper or CAD plans and you turn them into a 3D model for machine control, you are literally building the 3D project in your office before you go out to the site.  This gives you the opportunity to catch the errors, missing data or discrepancies in the plans while you are still in the planning stages.  This is a huge advantage in helping to limit your liability on a project especially when the errors or discrepancies are not your fault.  When you find almost all these errors and discrepancies before you start to build a project, this gives you time to make the contractor aware of the issues and usually gives you time to ask the engineer or owner to correct the issues or at least offer clarification.  By solving these issues before construction, you are actually limiting your liability and in reality you are helping the project engineer limit their liability and you are helping the contractor eliminate issues before they arise.  There is certainly a value to that.   

One of the other advantages of building a 3D representation of the project before you start construction is the ability to view and assess the project early on.  It is a lot easier to view a project in 3D to gain an understanding of that project than it is to look at a set of paper plans and fully understanding what is involved in building the project.  It is also much easier to view a 3D model and see errors.  Most software has a “fly over” or “drive over” feature which allows for easy visualization of the site.  When you look at a project in 3D and you see a spike in the surface, you immediately know you had a zero elevation somewhere in the surface.  It is very easy to visualize these errors.  Even when you transpose a number and have a 544 contour elevation instead of a 455 elevation, visually this is very easy to see.  When you have a 3D surface, not only can you easily visualize that surface, but you can also contour that surface at a very small interval, such as 0.1 feet and see the variations and undulations very easily.  Again, you are making it easier to see any possible errors in a surface and in turn, making it easier to resolve those errors. 

I believe, in many cases, land surveyors are still using points to do their construction layout.  If you are massing grading a site, you probably still interpolate an elevation from contours and then have your field crew layout and stake the point and then grade to the point elevation.  Wouldn’t it make more sense to create a 3D surface and then stake to the elevation of the surface?  If you create the surface and stake to the surface, I think there is less potential for elevation errors as compared to interpolating the elevations and then taking those elevations and typing them into the point information.  If you still want to use points, you can use the point information to navigate to the location on the ground, but if you use the surface elevation for your vertical guidance, there is less chance for elevation errors.  The 3D model also allows you to get a cut or fill anywhere on the project site, not just at your calculated point locations.  Every step in your process that you can eliminate or eliminate the chance for error, you limit your liability. 

Building a 3D model is nothing more than building a 3D surface of the project, along with the line work and any other data that may be necessary to layout the project.  I believe that when you create a 3D surface of a project you have a better chance of seeing potential errors and therefore limit your liability on that project.  If this is true for land surveyors performing construction layout, why wouldn’t it also be true for machine control models?  I personally believe that creating 3D models and 3D surface files of project are a good way to decrease or limit our liability on a project. 

3D models are simply a tool and that tool offers us a way to visually see any errors and eliminate those errors before we go into the field.  3D models and site calibrations certainly don’t expose us to more liability, if they are done correctly and we have the proper systems checks in place.  Currently, I am not aware of any cases where a land surveyor or the creator of a 3D model has been held liable for errors on a construction project because of the file being wrong or the site not being properly calibrated.  If you are using 3D models or 3D surfaces and you have the proper procedures and system checks in place and you are repeatedly checking your work, I believe you are actually decreasing your chances for an error and ultimately limiting your liability. 

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