The disclosure includes embodiments for generating a real-time high-definition (HD) map for an ego vehicle using wireless vehicle data of a remote vehicle. In some embodiments, a method includes receiving a V2X wireless message which includes remote GPS data and remote road parameter data of the remote vehicle. The method includes retrieving ego GPS data of the ego vehicle. The method includes generating ego road parameter data describing an initial estimate of a geometry of a road on which the ego vehicle is located. The method includes fusing the ego road parameter data and the remote road parameter data to form fused road parameter data which describes an improved estimate of the geometry of the road that is more accurate than the initial estimate. The method includes generating a real-time HD map based on the remote GPS data, the ego GPS data, and the fused road parameter data.