Ground Control Points (GCPs) Best Practices

What materials, size, and location you should set GCPs for your LiDAR Flight

Making Aerial Targets

Material, Size, Pattern

Our recommendation is to use a sizeable, square, target material. 2 foot by 2 foot or 4 foot by 4 foot plywood is a great option.

To color the plywood simply use paint to color it black and white. Take a look at the below patterns for inspiration.

We strongly caution against using retro-reflective materials (reflective tape) for your targets as it creates a thick cloud reflection around the target.

The basics to a good aerial target is something of high contrasting color (black and white) that is large enough to be seen from the air.

 

RGB View:

Intensity View:

Placing Your Targets

The best place to set your aerial targets is in a flat, open area that you can easily place the targets without them wobbling or being blocked from the sky. We do NOT recommend placing your targets on the back of curb, on small feature items (fire hydrants, water meters, junction boxes, etc) because you want the target to be viewed as ground so your DEM and accuracy report read properly. Placing your GCP on the back of curb will most likely cut out your GCP points from the DEM and you'll see a 6" delta from "ground" to GCP. Avoid tall grass since placing your target on it provides wiggle room for the target during flight.

Flying Your Targets

If you really want to lock in your final point cloud to your GCPs it is recommended that you make a manual flight pass above your GCP at a lower altitude. Be sure to fly slowly for the highest point density. A recommended height and speed is around 30 m (<100 ft) and 2 m/s (<4.5 mph). A good time to do this would be before or after a battery hot swap and using a target that is close to your LZ. 

See the below screenshots for the difference between a high altitude GCP flight and low low altitude pass.

High Altitude

 

Low Altitude