  We present a method using Zernike moments for quantifying rotational and
reflectional symmetries in scanning transmission electron microscopy (STEM)
images, aimed at improving structural analysis of materials at the atomic
scale. This technique is effective against common imaging noises and is
potentially suited for low-dose imaging and identifying quantum defects. We
showcase its utility in the unsupervised segmentation of polytypes in a twisted
bilayer TaS$_2$, enabling accurate differentiation of structural phases and
monitoring transitions caused by electron beam effects. This approach enhances
the analysis of structural variations in crystalline materials, marking a
notable advancement in the characterization of structures in materials science.
