April-Tags are visual target markers (comparable to QR codes) that help with the automatic alignment of cameras or autonomous mobile robots, for example. Special April-Tag recognition software calculates the exact 3D position and alignment, which is then used for orientation. The rough black-and-white patterns are also recognizable from long distances.
In robotics, they enable fast, cost-effective, and accurate localization and orientation. This also makes them the ideal alternative in environments where GPS or other navigation aids do not work reliably.