By: Thiago Santos
We’re encoding millimeter precision into HD Vector Maps that define Protobuf (PBF) for serialization designed to encode data with variable precision, optimizing the data size for the exact resolution needed by the dataset.
Coordinates traditionally are represented in memory as double triplet (Latitude, Longitude, Altitude). Our HD map format turns real world coordinates into a local tile grid. This means a long sequence of coordinates is now represented as sequence instructions. This radically saves bandwidth for streaming data to a car and reduces storage size for larger area coverage offline.
The HD map format uses “pen” commands to move a cursor in the tile grid, making it possible to encode a coordinate into something as small as 32-bits integer. Describing a four points 3D line would look like:
MoveTo(+2,+2,+5)
LineTo(+0,+8,+3)
LineTo(+3,+2,+5)
LineTo(+1,+0,+2)
The local tile coordinates are then converted back to the source projection when decoding the vector tile, to be consumed by the autonomous navigation engine.
HD Vector Maps support encoding arbitrary metadata. This lets each automotive company or tier 1 customize for their proprietary HD map formats. A point representing a road traffic sign valid in only four countries in Europe could have properties like:
The metadata is flexible and can be used for encoding strings, numbers, arrays and serialized nodes used to reconstruct a connected road graph inside a car with full level of detail.
The data is tiled in small pieces, distributed with low latency around the globe and receive partial updates in real-time as the road network gets smarter. Basically this brings Snapchat level scale for HD automotive maps, giving your fleet the latest up-to-date maps, in the fastest way possible, anywhere in the globe.
The code to encode, decode, optimize, and visualize HD Vector Maps is open source. For example, take a look at vtzero, our favorite decoder for embedded devices. It has a small memory footprint, is highly performant and it is designed to minimize memory allocations. Our open source approach fosters a healthy ecosystem of tools and means OEMs and suppliers can modify functionality to fit their exact needs and then use the Mapbox platform for visualization and distribution of HD Vector Maps to global fleets of vehicles.
Millimeter precision HD Vector Maps was originally published in Points of interest on Medium, where people are continuing the conversation by highlighting and responding to this story.