Objectives  Flatness inspection during construction period is critical to ensure the floor perform its desired function after completion. There are some shortages in traditional floor flatness measurement methods based on straight edge or levelling instrument, for example, not all locations in area can be measured and the measurement speed is slow, so that these methods can not fit the fast and accurate flatness measuring requirement of oversized floor during construction.

  Methods  According to the features of target floor, which has large area and is not entirely solid, we present a rapid measuring and calculating method for floor flatness based on inertial navigation system and total station. First, we collect inertial data by inertial measurement sled, and observe the coordinates of the sled by total station. Second, we use Kalman filter to fuse inertial data and the unit̓s coordinates to solve locations and attitudes of trajectory points. Third, we calculate the flatness indicator according to the elevation of trajectory points.

  Results  Experimental results show that the proposed method has nearly equal accuracy comparing to levelling instrument, with significant improvement in speed performance.

  Conclusions  The proposed method can not only make flatness quality assessment for floor under construction, but also detect and locate the flatness abnormalities so that provide direction for floor grinding. This method has great practical value and a wide application prospect.