  Attitude determination is a popular application of Global Navigation
Satellite Systems (GNSS). Many methods have been developed to solve the
attitude determination problem with different performance offerings. We develop
a constrained wrapped least-squares (C-WLS) method for high-accuracy attitude
determination. This approach is built on an optimization model that leverages
prior information related to the antenna array and the integer nature of the
carrier-phase ambiguities in an innovative way. The proposed approach adopts an
efficient search strategy to estimate the vehicle's attitude parameters using
ambiguous carrier-phase observations directly, without requiring prior
carrier-phase ambiguity fixing. The performance of the proposed method is
evaluated via simulations and experimentally utilizing data collected using
multiple GNSS receivers. The simulation and experimental results demonstrate
excellent performance, with the proposed method outperforming the ambiguity
function method, the constrained LAMBDA and multivariate constrained LAMBDA
methods, three prominent attitude determination algorithms.
