Ground Control Points for Precision Imagery

With any form of data collection, there is uncertainty. For instance, today’s Global Positioning System (GPS) enabled smartphones are typically accurate to within a 4.9 m (16 ft.) radius under open sky. This radius matters in precision agriculture, when growers often want to consistently monitor thousands of plants week after week, year after year!

To address this issue, we at Pollen Systems turn to technology like Ground Control Points (GCPs) to achieve the highest confidence in our imagery location accuracy. Our GCPs are 2’ x 2’ aluminum plaques that are secured to the ground by a metal spike and placed to be visible from above, allowing us to align aerial images with great precision. GCPs can be geolocated down to the centimeter which enables us to track plant and tree canopy growth to centimeter accuracy.

When considering a GCP installation, the following are highly recommended:

• Minimum of 5 GCPs, 4 placed around the perimeter of the area and 1 interior

• No more than 1500 feet to the nearest neighboring GCP

• Even distribution, placed to include high and low elevations

• Placed with 360-degree clear view of the sky, minimizing obstructions and shadow

We work closely with growers to ensure the GCP locations we recommend suit their needs. Once installed, we ground-truth the center of each point with survey-grade accuracy so we can use them to consistently align images season after season.

While most often used with drone imagery, high-resolution fixed-wing imagery also yields effective (although not quite as precise) results. Such reliable location data opens the door for many useful analytics, including change detection on a per-plant level and facilitating differential harvest of specific areas within a site.

If you want to know more about Ground Control Points for your field, please drop us a line at info@pollensystems.com or call us at (888) POLLEN8. Remember to keep learning and keep growing!