Wholi', some of the modern toys are so clever that they can provide an altitude indication using methods less crude than GPS height.
Given the present position of the aircraft, a 3-D geographical database knows the elevation of the immediate terrain and and can apply the radalt (radio usually, not radar) indication to that to obtain an altitude amsl. The problem, though, is that whilst this is probably pretty accurate, altimeters work on ISA lapse rates etc as a standard, so everyone must 'speak the same language' - particularly in RVSM airspace. But this 3-D geo-database information can at least be used to set the CCWR scanner tilt to the optimum value, avoiding the need for barely-trained people-tube co-piglets to learn the art of weather radar control....
The radar altimeter indications are going to be rushing up and down like the drawers of a lady I once knew at RAF Valley, but even faster (if that were possible).
One of the 'Sandymount set', perchance?