As I know internally any GPS reciever solve equation and get X,Y,Z and VX,VY,VZ in orthogonal coordinates WGS-84 system.
But in Android API I get only VX,VY,VZ projection to north-east plane (Location::getSpeed, Location::getBearing), so
How can I get full 3d vector of speed?
Based on what getAccuracy calculated for GPS, GDOP, VDOP or what?
As I remeber, and as you can find in the android docu, getAccuracy is related to horizontal accuracy.
From the DOP values its is more or less related to HDOP. But the chip manufacturers, which calculate the horizontalAccuracy estimate, do not specify how they internaly calculate that value. Nor they are willing to tell.
Your first sentence probably simplifies things. This might be valid for a demonstration modell of a GPS receiver.
In practise speed (over ground) considers, the doppler effect, too, which then gives more precise speed than just evalution the location change per time.
"How can I get full 3d vector of speed?"
I doubt you can get it. You can try to self caluclate by evalutaing altitude(m) change per time, for higher vertical speeds, like airplane, that might work.