  In this paper we present methods for triangulation of infinite cylinders from
image line silhouettes. We show numerically that linear estimation of a general
quadric surface is inherently a badly posed problem. Instead we propose to
constrain the conic section to a circle, and give algebraic constraints on the
dual conic, that models this manifold. Using these constraints we derive a fast
minimal solver based on three image silhouette lines, that can be used to
bootstrap robust estimation schemes such as RANSAC. We also present a
constrained least squares solver that can incorporate all available image lines
for accurate estimation. The algorithms are tested on both synthetic and real
data, where they are shown to give accurate results, compared to previous
methods.
