What does the red straight line in the navigation mean?

[GriffinAnn]

Red line indicates the traffic flow condition on the road, where red represents congestion. Below is relevant information: 1. Components: The automotive GPS navigation system consists of two parts. One part is composed of the GPS receiver and display device installed in the vehicle; the other part is the computer control center, with both parts connected via positioning satellites. 2. Working principle: In GPS observation, the distance from the satellite to the receiver can be obtained. Using the distance formula in three-dimensional coordinates and three satellites, three equations can be formed to solve for the position of the observation point. Considering the error between the satellite clock and the receiver clock, there are actually four unknowns: X, Y, Z, and clock difference. Therefore, a fourth satellite needs to be introduced to form four equations for solving, thereby obtaining the longitude, latitude, and elevation of the observation point.