The flatness measurement of a large 2-D flat work- piece such as a satellite solar panel substrate is a key problem in its manufacturing process. Based on the current measuring methods and the actual engineering project, a new noncontact high-precision, low-cost large 2-D flat workpiece flatness measuring system is developed, in which the techniques of oblique optical triangle measuring structure, virtual measurement datum plane, and error self-correction are adopted. By means of the oblique optical triangle measuring structure that is first proposed, the measuring area and resolution of the measuring system can be greatly increased. Meanwhile, on the basis of the techniques of virtual measurement datum plane and error self-correction, the noncontact high-precision, low-cost flatness measurement can be realized on a nonprecise large metallic platform. Experimental results on the satellite solar panel substrate indicate the correctness and effectiveness of the proposed noncontact flatness-measuring system of the large 2-D flat workpiece. Although the specific application of the satellite solar panel substrate is presented in this paper, the proposed measurement techniques and measuring system could be applied independent of the nature or use of the large 2-D flat workpieces. [ABSTRACT FROM AUTHOR]