AF wrote:
Where are you getting your information? Your matter-of-fact presentation of it is a bit concerning, given the error in your statements.
Maybe are talking about different things? From my point of view, the discussion began with your claim that receivers could correct for ionospheric delays if they had access to the P code. I replied that access to the P code is not what makes that possible — it is the availability of signals on different frequencies. That is really my only claim. Then I guess that both of us have started to argue about other things.
In any case, I was not aware of the civilian L2C signal. According to Wikipedia, the first satellite with that capability was launched in 2005, so before that there was no possibility for civilian receivers to do ionospheric corrections. Do civilian receivers (including IFR navigators) typically use the L2C signal today?
AF wrote:
My humble opinion would be that velocity is provided in 2D for reasons of navigation (think ETE and so on).
Also a few years ago, when GPS wasn’t that accurate, there was always 1 dimension sacrificed for the benefit of the accuracy of the other two.
Naturally altitude was sacrificed so that time, lat & long would be as accurate as possible.
Perhaps that has changed, but it would seem to lead to the conclusion that a lot of receivers would use a 2D position to interpolate velocity.
Peter wrote:
It is not calculated by the device, by taking consecutive position points and the time from one to the next. That would produce an inaccurate result with a lot of jitter.
That’s not true. General GPS receivers output new coordinates every second. All you need to do is take a few-second-average of the calculated speed (distance over time), and you eliminate the jitter. Remember too that time is incredibly accurate in GPS. We’re talking nanoseconds.
