The spot mode is one of the operation methods used in frame aerial cameras. The mode can point at interest objects via rotating scan mirror in position angle and depression angle directions and can view objects from different directions. In this paper

the geometrical model of a camera is presented and the relative coordinate axes are chosen. Then

a mathematical model for computing the image velocity from track coordinate system to image plane coordinate system is established. To compute the compensation velocity

the object velocities under aircraft coordinate axes and the velocities under compensation coordinate axes are computed and the visual axis length is also calculated

then the compensation angle velocity is obtained. Finally

the image plane revolution mechanism's function is explained in detail. The scan mirror and image plane revolution mechanism are incorporated in frame attitude compensation method based on spot mode. The numerical values calculated by coordinate conversion will provide the references for IMC engineering application.