The invention relates to a system for estimating the spatial position (pose) of a tool (2) within an object (1), particularly in the form of a human bone that is to be machined with said tool, comprising: a sensor (21) being designed to be coupled to said tool (2), which sensor (21) is further designed to generate an sensor output signal (31) upon machining of said object (1) along an actual trajectory (30), which sensor output signal (31) depends on a material property of said object along said actual trajectory (30), an analyzing means being designed to determine a correlation between said sensor output signal (31) upon machining said object (1) and a plurality of pre-determined candidate output signals (42), each candidate output signal (42) being generated in beforehand using said material property along an associated model trajectory (40) in a model of said object (1), and wherein said analyzing means is designed to estimate a spatial position of the tool (2) within the object (1) using the model trajectory (40) whose associated candidate output signal (42) has the highest correlation with the sensor output signal (31), for instance. The invention further relates to a method for estimating the pose of the tool (2), as well as a computer program product.