In the stereoplotter, the origin of the axis system is referred to as what?

In a stereoplotter, the upper nodal point serves as the origin of the axis system. This point is crucial because it represents the position of the optical system of the stereoplotter, where all lines of sight converge. When creating stereoscopic pairs of images, the upper nodal point allows for the correct interpretation of the three-dimensional relationships between points in the landscape being surveyed. An understanding of this concept is essential for accurately handling stereoscopic data and ensuring that the measurements and interpretations of terrain features are precise.

In contrast, the other points mentioned do not represent the origin of the axis system within a stereoplotter. The lower nodal point, for instance, has different geometrical significance related to the imaging system, while the central nodal point refers to a different aspect of the optical arrangement. The base nodal point, while similar in terminology, is not recognized as the primary point of reference for the system's axis. Thus, understanding the role of the upper nodal point is integral to the functionality and accuracy of stereoplotting techniques in surveying.