This paper presents a method to analyze 3D displacement data captured by digital image correlation (DIC) method over a long period of time. It allows monitoring of an object when a 3D DIC setup is not fixed in the same position between a consecutive series of measurements. An implementation of the data merging procedure is described and a proof of concept is provided using example measurements for both a numerical model and a real experiment in laboratory conditions. We evaluated the accuracy and discuss the main sources of errors. The obtained results prove the method is feasible for in situ long-term measurements and monitoring in industry and civil engineering.