1. Lecture 23 – Versions of ITRF, WGS 84, and their relationships to NAD 83
9 April 2009
GISC3325

2. Dilution of Precision
A planning measure measuring the effect of satellite geometry wrt the satellite constellation. Smaller values are better.
PDOP – Position (East, North and Up)
GDOP – Geometric (E,N,U and Time)
VDOP – Vertical (Up)
TDOP – Time (Time)
DOP combined with UERE to estimate positioning accuracy.

3. SKYPLOT

17. Antenna Phase Centers

22. WGS 84

23. WGS 84 and NAD 83 When first implemented they were equivalent.
NAD 83(1986) = WGS 84
WGS 84 does NOT use the GRS 80 reference ellipsoid.
Both NAD 83 and WGS 84 do not include a provisions for velocities.
Over time, both systems have diverged.
Currently WGS 84(G1150) is compatible with ITRF but NOT NAD 83.

24. Maintenance of WGS 84

30. HTDP Toolkit Item

31. Unless you have a good reason to do so, use the velocities coded into this tool.