An error associated with graphical parametric operations

Abstract

In grid and moire analyses, patterns developed in a deformed body are sometimes superposed to obtain the difference of their parameters, as when it is desired to obtain velocities by superimposing two isothetic patterns. In this operation, an inherent difficulty develops because, as a consequence of the deformation, not all points can be matched. An error follows which is analyzed here. Means to avoid or to compute the error are suggested.