Abstract: To find tie points from semi-randomly distributed point clouds is difficult,though such a task can be completed much easier in terms of images.Therefore,conventional imageto-image registration algorithms are no longer valid,where tie points are the main features for calculating registration parameters.We take the collinearity equation as a strict mathematical model for registration,and replace point features by linear ones through the parametric form of a straight line.High accuracy registration results have been achieved by such a manner.Meanwhile,semi-quantitative analysis is conducted in terms of the relationship between the image resolution and the LiDAR point density,which,to the author's best knowledge,has never been performed in literature.