What Are GCPs? Tips for Creating Better GCPs

If you have ever worked with drone mapping software, you are likely familiar with ground control points (GCPs). GCPs are used in the surveying, construction, and design industry to various extents The main reason GCPs are used is to increase the accuracy of drone maps. 

If you are among the people who do not know what drone GCP targets are and how you use them, then you’ve come to the right place. In this article, we will discuss what GCPs are and provide some tips for creating good ground control points for photogrammetry projects. 

What Are Ground Control Targets? 

Ground control points, in surveying terms, are the known locations within an area of interest. These points are identified on the ground so that they can be visualized in pictures taken from drones by placing targets on the ground directly above on top of the ground control points. The targets have a pattern that points directly to the center of the target in some way so that the exact coordinate can be located in the picture.

The term “GCPs” can also be used to describe these targets themselves, which can be confusing. The GCPs are placed throughout the entire area for maximum coverage, with the minimum GCPs required for most maps being five total GCPs, with one at each corner of the map and one in the center. The GCP targets and their perspective coordinates are then used to aid the drone mapping software for accurately positioning the map in the real world around it, providing a way to scale the map appropriately so that the map can be used to make accurate measurements.

Why It’s Important To Delineate GCPs? 

Some of the most important factors to consider when placing GCPs are: 

• Are the targets visible in their surroundings?
• Is the size large enough to be visible from the images taken by the drone, aircraft, or satellite? 
• Also, Is the GCP made of sturdy and durable material? 
• Is the GCP properly secured?
• Does the GCP have a unique number or identifier so that the coordinates of the GCP can be matched if needed?
• Is the GCP antireflective to reduce glare on sunny days?
• How does the GCP perform when precipitation is present?
• Is the GCP portable and easy to carry?
• Does the GCP need to be used over a long period? 

These are just some of the important things that need to be considered. These factors could affect the quality of your project and its deliverables. 

3 Prime Tips For Better GCP Results

Tip #1: Master Your GCP Placement

The most important tip you need to consider when using GCPs in your projects is the placement of your GCPs. The location of your GCPs is quite important when it comes to drone mapping. The targets must be visible and easy to identify in the images. Additionally, you should try to achieve an even distribution of the targets across the map with a GCP at each corner of the map and at least one GCP in the center of the map.   

Tip #2: Create Preflight Planning for Your GCP Mapping Projects

Is your project in the middle of an active construction zone or busy roadway? If this is the case, your GCPs should be placed intelligently out of the way of the activity in the area. Locate areas where they will be safe from the project site or, even better, outside it. Oftentimes, it may be easier to find a safe space for your targets at the extreme perimeters of the sites; which makes having proper control in the center of the site challenging. Once your GPC locations are set, make sure you set your flight duration as needed for the best outcomes.

Tip #3: Make the GCPs Easily Recognizable

With a handheld camera or phone, take pictures of each ground control target and include them with the survey report. This makes it easier for the GCPs to be identified manually if needed during post-processing. Having numbered GCPs is useful when attempting to match each GCP with its corresponding coordinates; which can quickly become confusing in areas without many identifying features. 

With these tips, you’ll be sure to be a GCP expert in no time!