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  • Writer's pictureHammer Missions

How to use Ground Control Points (GCPs) for Drone Mapping?

Updated: Dec 18, 2023




Overview

GCPs (Ground Control Points) have become an increasingly popular method for you to capture highly accurate 2D maps and 3D models using drones. Mapping accuracy can come in different shapes and forms. It's important to realise that GCPs are generally a useful tool to achieve geo-referencing (absolute) accuracy in projects, and generally a good fallback tool in case RTK / PPK processing options are unavailable.


In this guide, we'll go through the step by step process on how to plan, capture and process GCPs alongside your drone images in Hammer Missions to achieve cm-level absolute accuracy in your drone maps and 3D models

If you aren't familiar with GCPs and drone accuracy, please visit our guides below:




Step-by-Step Guide


If you prefer watching a video, checkout our step-by-step workflow here:




Step 1: Place & Measure your GCPs



The first step in the process of creating highly accurate maps is to place your GCPs on site. Generally speaking, it's good to have at least 3 GCPs evenly spread throughout your site. The number of GCPs required highly depends on the size of the target site, but we typically see 5-7 GCPs covering most sites.


Once placed, measure your GCP's location coordinates using GNSS base station equipment such as Emlid Reach RS 2 or DJI RTK2 Base Station.



img credit: heliguy.com



Step 2: Prepare your GCP location coordinates CSV file


Once you've captured the locations of your GCP markers, you should end up with a CSV file with the GCP names and locations. If your file is not in CSV format, it's best to convert it to this format and taking note of the different column headers. A typical CSV file might look like the following:



GCPs CSV File

Step 3: Upload your data


It's time to upload your drone data along with your CSV file. Navigate to the 'Data Analysis' tab in Hammer Hub. Select 'New Project' and upload your drone images.




Once the upload is complete, press the 'Process' button on the top right corner.


Step 4: Upload GCP Coordinates





In the processing workflow, tap on 'Use GCPs' option. Now upload the CSV file prepared in step 2. Choose your coordinate system and the type of your file. If your CSV file contains a header row, choose the 'ignore first line' option.


Step 5: Mark GCPs Pixels




The next step in the process is to mark GCP pixel coordinates. Once you have uploaded your CSV file, Hammer Hub will navigate you through your captured images to mark the GCP pixel coordinates. This process is done as it helps Hammer Hub correlate the location coordinates of the GCPs with their pixel locations.


Make sure to mark the GCP pixels as precisely as possible. Hammer Missions needs a minimum of 3 images marked per GCP.


Step 6: Process Your Data


If you have gone through steps 1-5, your data is now ready to be processed. Tap on the 'Process' button to kickstart the processing.


The processed map or model should be available for you to use in a few hours depending on the size of your dataset.


Summary


We hope the article helps you understand the GCP workflow in Hammer Hub.


If you'd like to learn more about how to capture high-quality data and get the most out of your drone flights using our cloud-based platform, please feel free to visit our learning resources.


To learn more about our enterprise solutions, including mission collaboration, data processing, and AI solutions, don't hesitate to get in touch with us at team@hammermissions.com.

We look forward to hearing from you.

— Team at Hammer Missions


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