I spoke to the guy at Navtech (post #1) and they get true heading to 0.5 of a degree by comparing the carrier phase. It is not done by getting two GPS positions and working out the heading.
They get pitch, roll & yaw (heading) measurements in one go.
tomjnx wrote:
Urgh no, pseudoranges are the only thing the GPS measures (unless it has augmentation input, like barometric pressure, gyro, wheel revolution sensors), so it is used all the time. Pseudo because it’s not actually a range, but the signal propagation time for the satellites to the receiver converted to distance (with some errors, like ionospheric added)
Hmmm. Both the Oxford Aviation Academy ATPL manual and the PPL/IR PBN Manual state that the term “pseudorange” is used only when calculating the initial fix, as the receiver does not have the correct time at that point.
The Wikipedia article you linked to also says that the term pseudoranges is used “with unknown receiver clock offset”.
Airborne_Again wrote:
The pseudorange measurements are only used for the initial fix, are they not?
Urgh no, pseudoranges are the only thing the GPS measures (unless it has augmentation input, like barometric pressure, gyro, wheel revolution sensors), so it is used all the time. Pseudo because it’s not actually a range, but the signal propagation time for the satellites to the receiver converted to distance (with some errors, like ionospheric added)
tomjnx wrote:
Yes, that’s the whole point of the GPS receiver firmware, it makes “educated guesses” (educated through pseudorange measurements) about your position, your velocity, your track angle, etc.
The pseudorange measurements are only used for the initial fix, are they not?
what_next wrote:
But this is because the software in your device makes “educated guesses” about what you are doing derived from your previuos movements.
Yes, that’s the whole point of the GPS receiver firmware, it makes “educated guesses” (educated through pseudorange measurements) about your position, your velocity, your track angle, etc.
Jan_Olieslagers wrote:
For the the gps track and ground speed readings to become erratic, one must move slower than the average pedestrian.
But this is because the software in your device makes “educated guesses” about what you are doing derived from your previuos movements. And it gets enough position measurements to perform some averaging while you move slowly. Right now I am building a quadcopter drone with my son and we are getting all these issues discussed here…
Perhaps. It might also be for lack of electrical power to feed all those modern gizmo’s 
Actually, my self-brew gps, basing upon a standard cheapish Hi-204 receiver, has worked very well even when cycling – and though I am from the country of Eddy Merckx, I am not a very fast cyclist. For the the gps track and ground speed readings to become erratic, one must move slower than the average pedestrian. So even in the lowest powered Cub there should be no issue.
But anything which moves slowly or not at all will get erratic track/heading and speed readouts.
Is that why the Super Cub community tends to use charts and compass?
If mankind didn’t use freely available resources for purposes they weren’t made for we’d still be making fire rubbing two sticks together and using the resulting smoke for communication….
what_next wrote:
I don’t know if they work well on fast moving vehicles like aircraft.
Why shouldn’t they? Compared to the speed at which the satellites move, even fast aircraft are still pretty stationary.
