ARTag, a fiducial marker system using digital techniques

Fiducial marker systems consist of patterns that are mounted in the environment and automatically detected in digital camera images using an accompanying detection algorithm. They are useful for augmented reality (AR), robot navigation, and general applications where the relative pose between a camera and object is required. Important parameters for such marker systems is their false detection rate (false positive rate), their inter-marker confusion rate, minimal detection size (in pixels) and immunity to lighting variation. ARTag is a marker system that uses digital coding theory to get a very low false positive and inter-marker confusion rate with a small required marker size, employing an edge linking method to give robust lighting variation immunity. ARTag markers are bi-tonal planar patterns containing a unique ID number encoded with robust digital techniques of checksums and forward error correction (FEC). This proposed new system, ARTag has very low and numerically quantifiable error rates, does not require a grey scale threshold as does other marker systems, and can encode up to 2002 different unique ID's with no need to store patterns. Experimental results are shown validating this system.

1. Introduction

Designing markers to add to the environment for robust detection in camera and video imagery is a computer vision application useful to situations where a camera-object pose is desired such as Augmented Reality (AR), position tracking, photo-modeling and robot navigation. 2D planar patterns can be added to the environment and recognized in the camera images. A 2D planar marker system consists of both a set of planar patterns and the associated computer vision algorithms to recognize them in an image. ARToolkit [5], [7] is a popular such system which contains a 2D planar fiducial marker system, it is used in many Augmented Reality applications and is used frequently in this paper for a basis to evaluate ARTag.