Abstract: In response to the common problem of projection deformation exceeding the limit in expressway plane control survey,this paper analyzs the causes and characteristics of projection deformation in the plane control network of east-west long span expressways.It proposes a method for determining the projection control threshold and this method has been test that it is convenient to determine the effective range of the compensatory projection plane.Two parameters are defined for the optimal compensatory projection plane.Furthermore,a method for quickly determining the optimal solution of the compensating projection plane is proposed.It designs a technical route for determining the optimal solution for compensating projection surfaces.The maximum projection deformation of the optimal compensatory projection surface determined by the proposed method is 17.7 millimeter per kilometer and the control effect of the projection deformation of the optimal compensatory projection surface on the reference ellipsoid surface is between 10.4~14.4 millimeter per kilometer based on the specific engineering example dataspecific data.It is shown that the optimal compensatory projection plane has a significant effect on controlling projection deformation compared to the limit of 25 millimeter per kilometer.The research results of this paper have certain practical value in the projection deformation control of expressway control networks.

Key words: projection deformation, control, threshold, optimal compensatory projection plane, expressway control network