One of our most common client questions is “ Why do you need a surveyor to measure ground control? So and so said they don’t need it for my project” The short answer is “To give you the best results”. Really, it is a little more complicated than that. Without taking a deep dive into the details there are a few reasons we need ground control.
First, it orients our flight data with the survey control system used on your project. Basically, it allows us to match the survey or orthographic work you have done in the past, or plan to do in the future. The X,Y,Z (latitude, longitude, altitude) values on our orthographic photos and 3D models will align with all of your CAD design work. We can match local coordinate systems or any common system (state plane, UTM, etc…). If we are aligned to a common public coordinate system it is easier for other service providers to use our data as well. Our photos and 3D models can be used by a surveyor for stakeout, in CAD drafting, 3D modeling or we can even build a detailed machine control model for your contractor – all starting with a UAV flight.
Second, ground control reduces deformation in your photo and model. You will be able to take accurate measurements across your site, right from the photo. Some studies show deformation as high as 9% over large flights without ground control. That might be ok if all you want is a pretty picture but we expect more from our data.
For the relatively small cost of good ground control why wouldn’t you use it?