We’ve all experienced the simple but exceptional functionality of using a Barcode to scan items at the grocery store. This quick, electronic identification is likely under-appreciated until you’re forced to punch in the item number for a russet potato at self-checkout. Similarly, QR codes have saved smartphone users abundant frustration by allowing them to fast-track to an advertised website or even dinner menu – rather than punching in colons, slashes, and the remaining randomized characters that make up a web address. Now, imagine if this same idea could be used to streamline flying your Drone. When multiple moving parts and processes are calculated at a mile a minute- such a simple concept could be highly beneficial. But what if more information than just identification could be transferable through such a “tag”? This is where April Tags come in! 

An April Tag is a fiducial marker that is used in robotics, augmented reality, and camera calibration thanks to its robust ability to offer clear detection based on lighting conditions, view angle and orientation. This allows such robotics interacting with April Tags to establish its precise 3D orientation relative to the tag, and use that information to operate and make decisions. For an agile aerial robot like the DEXI, April Tags are a great tool to orientate and assist in interesting tasks.

In this course, DroneBlocks co-founder Dennis Baldwin walks us through enabling April Tag Detection in the DEXI ROS2 project so that the DEXI can read April Tags in both Node-RED and Python. Students will be amazed to see how quickly markers are detected when in the field of view of the Raspberry Pi camera. By the end of the course, Dennis will have your DEXI lighting up its LEDs based on tag detection, which could stand as a metaphor for multiple applications of how April Tags could be used practically. In a future course, Dennis plans to transfer this exercise to allow the DEXI to determine certain poses in relation to the tags based on the detection of various April Tags placed around the environment. All of this becomes possible thanks to the DEXI’s ability to add the Raspberry Pi2 camera attachment. 

This lesson is inspired by this year’s Advanced Vertical Robotics competition, where student teams will be utilizing the DEXI to read April Tags as part of the competition scenario. This course also builds on the knowledge you have gained in the DEXI Sensor Wiring and Programming course, so please be sure to check it out first!