Bundle adjustment with additional constraints applied to imagery of the Dunhuang wall paintings

In the digital conservation of the Dunhuang wall painting, bundle adjustment is a critical step in precise orthoimage generation. The error propagation of the adjustment model is accelerated because the near-planar photographic object intensifies correlation of the exterior orientation parameters and the less than 60% forward overlap of adjacent images weakens the geometric connection of the network. According to the photographic structure adopted in this paper, strong correlation of the exterior orientation parameters can be verified theoretically. In practice, the additional constraints of near-planarity and exterior orientation parameters are combined with bundle adjustment to control the error propagation. The positive effects of the additional constraints are verified by experiments, which show that the introduction of weighted observation equations into bundle adjustment contributes a great deal to the theoretical and actual accuracies of the unknowns as well as the stability of the adjustment model.