Surveying subsystem comprising a camera module and a control and evaluation unit, wherein the surveying subsystem is adapted to be used as part of a surveying system that is adapted to determine positions of a position measuring resource, • the camera module comprising at least one camera for capturing images, • an inertial measuring unit being associated with the surveying subsystem in a fixed spatial relationship relative to the surveying subsystem, • the control and evaluation unit having stored a program with program code so as to control and execute a calibration functionality in which - when moving along a path through a surrounding - □ inertial measuring data is gathered while moving along the path, and □ camera-based localisation data is generated, wherein · a series of images of the surrounding is captured with the at least one camera, the series comprising an amount of images captured with different poses of the camera, the poses representing respective positions and orientations of the camera, and · a SLAM-evaluation with a defined algorithm using the series of images is performed, wherein a plurality of respectively corresponding image points are identified in each of several sub-groups of images of the series of images, characterised in that • the SLAM-evaluation comprises, based on resection and forward intersection using the plurality of respectively corresponding image points, □ building-up a reference point field comprising a plurality of reference points of the surrounding, wherein coordinates of the reference points are derived, and □ determining the poses for the images; and • the calibration functionality comprises deriving calibration parameters for the inertial measuring unit based on the gathered inertial measuring data and the camera-based localisation data. • the camera module comprising at least one camera for capturing images, • an inertial measuring unit being associated with the surveying subsystem in a fixed spatial relationship relative to the surveying subsystem, • the control and evaluation unit having stored a program with program code so as to control and execute a calibration functionality in which - when moving along a path through a surrounding - □ inertial measuring data is gathered while moving along the path, and □ camera-based localisation data is generated, wherein · a series of images of the surrounding is captured with the at least one camera, the series comprising an amount of images captured with different poses of the camera, the poses representing respective positions and orientations of the camera, and · a SLAM-evaluation with a defined algorithm using the series of images is performed, wherein a plurality of respectively corresponding image points are identified in each of several sub-groups of images of the series of images, characterised in that □ inertial measuring data is gathered while moving along the path, and □ camera-based localisation data is generated, wherein · a series of images of the surrounding is captured with the at least one camera, the series comprising an amount of images captured with different poses of the camera, the poses representing respective positions and orientations of the camera, and · a SLAM-evaluation with a defined algorithm using the series of images is performed, wherein a plurality of respectively corresponding image points are identified in each of several sub-groups of images of the series of images, · a series of images of the surrounding is captured with the at least one camera, the series comprising an amount of images captured with different poses of the camera, the poses representing respective positions and orientations of the camera, and · a SLAM-evaluation with a defined algorithm using the series of images is performed, wherein a plurality of respectively corresponding image points are identified in each of several sub-groups of images of the series of images, • the SLAM-evaluation comprises, based on resection and forward intersection using the plurality of respectively corresponding image points, □ building-up a reference point field comprising a plurality of reference points of the surrounding, wherein coordinates of the reference points are derived, and □ determining the poses for the images; and □ building-up a reference point field comprising a plurality of reference points of the surrounding, wherein coordinates of the reference points are derived, and □ determining the poses for the images; and • the calibration functionality comprises deriving calibration parameters for the inertial measuring unit based on the gathered inertial measuring data and the camera-based localisation data.