Quality Control for Terrain Modeling

[ewhite]

1. A grading contractor has a grading plan provided to them by a firm that doesn't use 3d modeling.

2. Said grading contractor asks my company to provide a 3D terrain model that they can use in their GPS controlled equipment.

What I am looking for is a way to create some quality control to the final product. How do we check the model to ensure that what we are providing to the contractor is an accurate representation of the other firms grading plan? What liabilities are acceptable? Has any other company out there had any experience or success with this?

[jpaulsen]

Assuming the grading plan consists of contours and spot elevations, you should make sure that your surface is accurate at those locations. Your surface should contain an x,y,z at every spot shown on the plans and every contour should be included in the surface.

Does the contractor expect accurate elevations where there are none on the plans? For example, if you have a two spot elevations 100' apart along a curb line does he want the surface to have an accurate elevation on the curb between those points?

If so, you will need to trace all grade breaks (curbs, gutters, sidewalks, ditches, flowlines, etc.) with feature lines using the elevations provided on the plans. I would be careful here though. You need some kind of CYA in writing. If you agree to provide interpolated data other than what is shown on the plans you are opening yourself up to liability.

[ewhite]

Thank you for your response.

The main thing that we are struggling with is at what point are you responsible for the design? What happens when the other firm is deliberately vague in certain areas, or provides you with a grading plan that is down right wrong? There is no chance for our firm to comment or review before it’s approved. There would definitely have to be some clever language in the scope of services contract, not to mention a signed indemnification agreement.

I don't believe there is any legislation (so far) requiring any sort of certification on a terrain model, so there is also the issue of providing the internal quality control, how do we assure a contractor that what we are providing is a workable terrain model.

[jpaulsen]

I think your safest bet is to make sure your surface is accurate where the grading plan shows spots and contours. Beyond that you should not be responsible for any interpolated data or for the integrity of the design.

Good luck. I'd like to know how this turns out for you.

[bhaugi]

I don't have a great answer, but this is a great topic. Even if you did do the design, it is so hard to stress the importance of this quality control check.

[scott.wagner]

This is a big issue that the industry is still trying to figure out. I've seen a lot of companies come up with language with the delivery transmittal that ends liability once the plan is handed over. (Prevents them from adding things to the CAD model)

One quick check is to check for holes/spikes in the model by flipping it in 3D. This will help catch any thing that could really hurt your earthwork.

I've done work in the past reviewing Civil 3D models for companies to make sure they match the plans and to make sure they are ready for giving to consultants/contractors. If you want to talk more contact me at mrscottwagner@yahoo.com

I am a PE in California, but I worked for 2 years with a reseller for Autodesk training Civil 3D and implementing the program. I even taught at Autodesk University on how to make sure your models are accurate. (Look at the class here:
http://au.autodesk.com/?nd=class&session_id=433) There are some definite tricks to making sure your model is tight before handing it out. Good luck and strip yourself of as much liability as possible.

[brian.hailey933139]

I agree with Scott. Strip the liability as much as you can. The best way to do this is to talk with your insurance carrier. Since they are ultimately responsible for your errors and omissions, they will want to protect you as much as possible.