Quantum has broadcast loud and clear the best practices regarding site control for your GPS machine control systems. When expanding your tech repertoire into drone data, (we have heard the Quantum Flight Pack is good) it is just as important for you to understand how Ground Control Points (GCP) are utilized and why they are necessary when collecting drone data.
Ground control is a target placed on the ground that can be seen in your drone photos. It is what ties your drone data to the "ground" and functions in much the same way as site control for your GPS system.
We have broken the Ground Control process down into five simple principles you can apply to ANY drone data project and ANY drone system. Click on each one for a separate post with a detailed explanation.
The center of the GCP target is measured with the GPS system you are using for that project. We can see the targets in your drone photos, it's what we use to align your drone data with your machine control model, the project plans and any other survey work that has been done on the site. Without ground control, at the very best, your drone data will only be within a few feet of the correct location horizontally and dozens of feet off vertically. Nowhere near close enough to make it useful for much of anything when it comes to measuring your progress against the construction plans.
Let's address the elephant in the GCP room --> There is a lot of buzz in the industry about PPK and RTK capable drones with very accurate photo geotags. They have their place and big potential, but you still can't beat the simplicity, low cost and reliability of standard ground control. You already have an expensive and highly accurate GPS base/rover system, may as well give it double duty in measuring ground control. Even with a PPK or RTK drone you should still have a few GCP's to guarantee your drone data will align with your machine control model. You rarely get a second chance to fly a constantly changing construction site.
On the right, is a photo of a good ground control target. Note it has a clearly defined center, a matte finish and contrasting colors that show up well in drone photos. The basic design you see below is how most good quality GCP's are designed. Also, notice how this target is very low tech. Remember, you will use the GPS rover already set up on site to measure in the center of the target. If a dozer or truck runs over this target, its unfortunate, but you are only out the price of a good lunch. Not a few hundred $$$.
It's ok to use ground paint in difficult to access or high traffic areas, but a good quality re-useable target is always best. If using ground paint, heavily paint the target and make it so the center will be easy to see from the air. Lightly painted or target colors that blend into the surface won't serve their purpose very well. Orange and blue seem to work well for most ground conditions.