GPS Toolkit Support Questions

[Abhay_Samant]

1.  Using GPS Toolkit , is it possible to write a trajectory script to accelerate upwards at an angle starting from a stationary point?

With GPS toolkit 2.0, it's possible to move from stationary point and accelerate upward at some angle. This could be done using a straight command by providing an initial heading at the beginning.

Here is an example of the kind of setting that you would need -

Front Panel Setting:
Initial Heading 45
Initial speed 0
Initial Vd 0

Syntax :-
Straight constant_heading distance duration altitude_change

Example 1: Climb motion (Only altitude change/elevation angle at  90deg with the LTP plane)
Straight constant_heading 0 100 1000

Example 2: Climb motion (elevation angle at  45deg with the LTP plane)
Straight constant_heading 1000 100 1000

Notes:
distance = cos(elevation_angle)
altitude_change = sin(elevation_angle)
Initial heading is with respect to LTP plane only.

2.  Some GPS receivers report a 7,168 day offset from what is being generated by the GPS Simulation Toolkit?

GPS time is transmitted as week number and time of week. The week number is a 10-bit number, which means it rolls over every 1,024 weeks, which is equivalent to the 7,168-day offset.  So, what is probably happening is that when GPS receiver manufacturers create a new firmware, they want it to last for as long as possible, so the assume that any GPS signals they are receiving cannot be in the past.

So, for example, if a firmware was created in 1995, they would interpret week number 947 as being in March 1998.
However, if a firmware was created in 2001, after the Aug. 1999 roll-over of GPS weeks, then they would interpret week number 947 as being in Oct. 2017.

In such a situation, GPS receivers will work fine with real GPS signals, but have this 7,168-day offset when you use them with the GPS RF simulator.