|VSI Labs will do a cross-country roadtrip this summer, ending at gthe Drive World Conference held from August 27 to 29. (Image source: VSI Labs)|
This August, autonomous vehicle (AV) research firm VSI Labs is embarking on the classic American cross-country road trip–with a twist. VSI will utilize their autonomous research vehicle for the 2,000-mile journey, driving from Minneapolis, MN, to Santa Clara, CA, where the Drive World conference will be held from August 27 to 29.
The purpose of this unprecedented project is to test the value of using HD maps and enhanced GPS technology to improve the performance and safety of highway autonomous driving applications. The team is also hoping to better understand how these technologies operate across varying terrains, weather, and driving conditions.
VSI has been testing its AV research vehicles at its lab facility and on public roads for more than two years. The team launched its second-generation AV research vehicle last October–the same vehicle they will take on the Drive West. The vehicle is a 2018 Ford Fusion equipped with Dataspeed’s by-wire control system, along with numerous other AV technologies. VSI engineers built a Linux-based computer installed inside the vehicle which acts as a domain controller for AV functions.
Because the Drive West will be the first experiment in which VSI attempts a cross-country drive in AV mode, the team began preparing for this project months in advance. VSI’s engineers will leverage some existing software developed for their standard testing, but they also needed to develop new software and methodologies that allow them to test outside of a geofenced area. We’ve detailed some of the preparations VSI engineers have been making to prepare the vehicle for the Drive West.
Dynamic Map Data Loading
VSI will use two main AV applications for the drive: adaptive cruise control (ACC) and lane keeping. These two applications utilize data from HD maps and on-board sensors, and the engineers have developed algorithms for these applications in-house. While VSI has done extensive research on lane keeping and ACC using HD maps, this research has always been conducted in a geofenced area. In previous tests, VSI engineers downloaded and processed the map data prior to testing. Because the upcoming Drive West spans more than 2,000 miles of highway roads, it was necessary to develop a method of downloading and processing map data during the drive.
To accomplish this, VSI wrote scripts to download the correct map data given the vehicle’s location at any given time. The script first checks to see if the file already exists, and only downloads the data if it has not already done so. After the new map data is downloaded, the map data must be processed to find a new target path for both lane keeping and ACC. Once a new target path is found using the new map data, the steering command slowly transitions from the current target path to the new target path. Although not strictly necessary, the gradual transition to the new target path allows the driver enough time to react in case any errors occurred in the loading of the new map.
Large-scale Map Distortion
One of the major difficulties with using HD maps over large distances is dealing with map distortion. While distortion is negligible over a small geofenced area, the distortion can seriously disrupt lane keeping when relying on centimeter-level accuracy of the map.
VSI engineers investigated whether this coordinate transformation was viable for driving across a large distance. The team graphed the transformed coordinates following the entire 2,000-plus miles west and saw that this transformation broke down over large distances due to the curvature of the earth.
After some research into alternate coordinate systems, they decided to proceed with the Universal Transverse Mercator (UTM) coordinate system, which breaks the earth into 6-degree longitudinal sections and gives coordinates in meters. A problem arises when considering they will be driving through 6 of these zones on the Drive West, and the easting value in the UTM coordinate system resets in each zone, meaning they would need to find a way to smoothly transition between zones.
UTM Zones from Minneapolis to Santa Clara. (Image source: VSI Labs)
After testing with autonomous control enabled while transitioning between UTM zones, all the code worked as expected, but interesting behavior was observed regarding the vehicle’s orientation with respect to the map. Because there is higher distortion at the edges of UTM zones, the offset angle VSI uses to correct misalignment of the IMU needed to be adjusted by nearly 2 degrees. The distortion inverses when changing zones, causing the offset angle to no longer be accurate enough to keep the vehicle centered in the lane, leading the vehicle to drift drastically to one side. To solve this, the engineers artificially translated their latitude and longitude coordinates and monitored the optimal offset angle in various areas within a UTM zone. They found that a simple linear relation between the longitudinal distance to the center of the UTM zone and the offset angle would suffice to dynamically correct for map distortion throughout a UTM zone.
Follow Our Journey
The preparations outlined above are a brief look into the extensive work done by our team of engineers. VSI will share more information, including all the results and findings from the ADW project at the Drive World Conference. You can also follow the journey through VSI's website or social media channels where we post photos and videos of the ADW.
Jacob Miller, is a Autonomous Solutions Engineers at VSI Labs .
This summer (August 27-29), Drive World Conference & Expo launches in Silicon Valley with North America's largest embedded systems event, Embedded Systems Conference (ESC). The inaugural three-day showcase brings together the brightest minds across the automotive electronics and embedded systems industries who are looking to shape the technology of tomorrow.