  Robust and accurate pose estimation is crucial for many applications in
mobile robotics. Extending visual Simultaneous Localization and Mapping (SLAM)
with other modalities such as an inertial measurement unit (IMU) can boost
robustness and accuracy. However, for a tight sensor fusion, accurate time
synchronization of the sensors is often crucial. Changing exposure times,
internal sensor filtering, multiple clock sources and unpredictable delays from
operation system scheduling and data transfer can make sensor synchronization
challenging. In this paper, we present VersaVIS, an Open Versatile Multi-Camera
Visual-Inertial Sensor Suite aimed to be an efficient research platform for
easy deployment, integration and extension for many mobile robotic
applications. VersaVIS provides a complete, open-source hardware, firmware and
software bundle to perform time synchronization of multiple cameras with an IMU
featuring exposure compensation, host clock translation and independent and
stereo camera triggering. The sensor suite supports a wide range of cameras and
IMUs to match the requirements of the application. The synchronization accuracy
of the framework is evaluated on multiple experiments achieving timing accuracy
of less than 1 ms. Furthermore, the applicability and versatility of the sensor
suite is demonstrated in multiple applications including visual-inertial SLAM,
multi-camera applications, multimodal mapping, reconstruction and object based
mapping.
