  Baseline generation for tracking applications is a difficult task when
working with real world radar data. Data sparsity usually only allows an
indirect way of estimating the original tracks as most objects' centers are not
represented in the data. This article proposes an automated way of acquiring
reference trajectories by using a highly accurate hand-held global navigation
satellite system (GNSS). An embedded inertial measurement unit (IMU) is used
for estimating orientation and motion behavior. This article contains two major
contributions. A method for associating radar data to vulnerable road user
(VRU) tracks is described. It is evaluated how accurate the system performs
under different GNSS reception conditions and how carrying a reference system
alters radar measurements. Second, the system is used to track pedestrians and
cyclists over many measurement cycles in order to generate object centered
occupancy grid maps. The reference system allows to much more precisely
generate real world radar data distributions of VRUs than compared to
conventional methods. Hereby, an important step towards radar-based VRU
tracking is accomplished.
