Generating a scanned-surface model representing a scanned surface includes various steps. For example, instrument model coordinates may be obtained that represent a position of the instrument in the 3D model. In addition, surface-distance measurements may be derived describing a distance from the scanned surface. Inertial measurements are also recorded. The instrument model coordinates, surface-distance measurements, and inertial measurements are correlated and filtered by a rules based selection process to determine scanned-surface model coordinates.