A method of identifying a surface point or region of an object to be measured by means of an optical sensor providing defined measuring conditions regarding emission of measuring light and reception of reflected measuring light in a defined spatial relationship. The method comprises defining a point or region of interest of the object, determining an optical property of the defined point or of the defined region and deriving an object information base on the optical property. The determination of the optical property is performed by optically pre-measuring the point or region using the optical sensor by illuminating the point or the region with the measuring light, capturing at least one image by means of the optical sensor of at least one illumination (Lr,Li) at the object and analyzing respective illuminations (Lr,Li) regarding position or appearance plausibility with respect to the measuring conditions of the optical sensor.