coordinates are fixed?

     A point, as you know, is only a mathematical concept; it has no dimensions. In essence, a coordinate point does not exist in a physical sense, it merely serves as an identifier for a specific, unique location within that coordinate system. These coordinate points mimic any moves that their origin does. They are conceptual points and remain in their exact relative positions to each other within that system.

     Fixed point coordination contains a set of inter-related, inter-coordinated points, which theorectically could remain forever in place, or until one selects a new random origin location. ( from somewhere within the existing coordination. )

     Each point would have its own unique coordinate position within the mathematical grid. These coordinate points never move in relationship to one another. There is not just THE one possible fixed point grid. Indeed, any coordinate point can be deemed as origin, and has choice of unit distance and orientation as well. An infinite amount of possible coordinate systems, not just Cartesian, each of unlimited extents, are mathematically obtainable, as well.
Coordinate points are never in motion, wrt their own origin; they are eternally fixed wrt their own origin.