When and Why Are GCPs Important?
When used correctly, ground control points greatly improve the global accuracy of your drone map. That is to say, they help ensure that the latitude and longitude of any point on your map corresponds accurately with actual GPS coordinates. This is important in situations where precision mapping and true global accuracy are needed. As we mentioned above, surveying companies generally use GCPs, because a high level of global accuracy is important in most of the work that they do. Virtual design and construction is another sector that often requires this level of precision drone mapping.
Landpoint, a surveying company based in Louisiana, uses ground control points when creating drone maps used for topographical surveying. Using GCPs on an 85-acre map, their team conducted an accurate aerial survey, saving over 80 man hours compared to traditional land survey methods.
Each drone mapping project is unique, and not all projects require a high level of global accuracy. Because of this, it is important to assess each project individually before you decide to take the extra step of using GCPs. But generally speaking, projects like geo-referenced overlays, design documents and land title surveys benefit from the use of ground control points. In an upcoming post, we’ll take a deeper look at which types of projects are best suited for using GCPs.
How to Construct a Ground Control Point
There is no one right way to make a ground control point. One important thing to remember is that the GCP must be easily visible in your aerial imagery. This is achieved by using high-contrast colors and by making sure the ground control point is large enough to be seen from your particular flight altitude. We generally recommend flying at 300 feet with a frontlap and sidelap of 70/75 when using ground control points. Keep in mind that this may change dependent upon the area you are mapping. Learn more by reading our recent post about mapping accuracy and reviewing our GCP support documents.
A number of companies do sell pre-made, portable ground control points. However, many drone users simply fashion their own.