The points of intersection between the fitted drop shape and the baseline are determined in all drop shape analysis methods for measuring the contact angle. These points of intersection correspond to the three-phase contact points of the system.
The ADVANCE Software determines the baseline from the video image of the drop with the help of discontinuities in the contour. These occur either due to the termination of the contour line itself or - in the case of reflecting solids - due to the transition between the drop image and its reflection.
The baseline can also be set manually however.
The mathematical description of the baseline depends on its shape: a linear equation for flat surfaces and a trigonometric function for rounded substrates.