“…Euclidean Distance sketch in spectral space, each pixel corresponds to a multidimensional spectral vector, and the angle between the two vectors is defined as spectral angle (Fig. 3) [23].The smaller the spectral angle is, the more similar the two spectra are and the more likely they are to belong to the same kind of features. Similarly, the Spectral Angle Distance makes full use of the information of the pixel in the spectral dimension, but different from the Euclidean Distance, the Spectral Angle Distance is not affected by the light, shadow and other conditions, that is, when the brightness value increases or decreases, its angular direction will remain unchanged.…”