The new method of separation of strains in elastic plane stress state, called the method of characteristics, is presented. The photoelastic experiment for determination of isochromatic order is supported by additional numerical procedure. To determine the fractional order of fringes, the automatic image process is applied.
"Computer-aided separation of strains in photoelasticity", Proc. SPIE 2342, Interferometry '94: Photomechanics, (30 November 1994); doi: 10.1117/12.195492; https://doi.org/10.1117/12.195492