  Adding fiducial markers to a scene is a well-known strategy for making visual
localization algorithms more robust. Traditionally, these marker locations are
selected by humans who are familiar with visual localization techniques. This
paper explores the problem of automatic marker placement within a scene.
Specifically, given a predetermined set of markers and a scene model, we
compute optimized marker positions within the scene that can improve accuracy
in visual localization. Our main contribution is a novel framework for modeling
camera localizability that incorporates both natural scene features and
artificial fiducial markers added to the scene. We present optimized marker
placement (OMP), a greedy algorithm that is based on the camera localizability
framework. We have also designed a simulation framework for testing marker
placement algorithms on 3D models and images generated from synthetic scenes.
We have evaluated OMP within this testbed and demonstrate an improvement in the
localization rate by up to 20 percent on four different scenes.
