apriltags

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AprilTags library

Detect April tags (2D bar codes) in images; reports unique ID of each detection, and optionally its position and orientation relative to a calibrated camera.

See examples/apriltags_demo.cpp for a simple example that detects April tags (see tags/pdf/tag36h11.pdf) in laptop or webcam images and marks any tags in the live image.

Ubuntu dependencies: sudo apt-get install subversion cmake libopencv-dev libeigen3-dev libv4l-dev

Mac dependencies: sudo port install pkgconfig opencv eigen3

Uses the pods build system in connection with cmake, see: http://sourceforge.net/p/pods/

Michael Kaess October 2012

AprilTags were developed by Professor Edwin Olson of the University of Michigan. His Java implementation is available on this web site: http://april.eecs.umich.edu.

Olson's Java code was ported to C++ and integrated into the Tekkotsu framework by Jeffrey Boyland and David Touretzky.

See this Tekkotsu wiki article for additional links and references: http://wiki.tekkotsu.org/index.php/AprilTags

This C++ code was further modified by Michael Kaess ([email protected]) and Hordur Johannson ([email protected]) and the code has been released under the LGPL 2.1 license.

• converted to standalone library
• added stable homography recovery using OpenCV
• robust tag code table that does not require a terminating 0 (omission results in false positives by illegal codes being accepted)
• changed example tags to agree with Ed Olson's Java version and added all his other tag families
• added principal point as parameter as in original code - essential for homography
• added some debugging code (visualization using OpenCV to show intermediate detection steps)
• added fast approximation of arctan2 from Ed's original Java code
• using interpolation instead of homography in Quad: requires less homography computations and provides a small improvement in correct detections

todo:

• significant speedup could be achieved by performing image operations using OpenCV (Gaussian filter, but also operations in TagDetector.cc)
• replacing arctan2 by precomputed lookup table
• converting matrix operations to Eigen (mostly for simplifying code, maybe some speedup)