source: ntrip/trunk/BNC/src/todo.txt@ 6812

Last change on this file since 6812 was 4282, checked in by mervart, 12 years ago
File size: 2.3 KB
Line 
1Todo's sorted by priority:
2
3(1) Should we spend time to improve BNC's convergence? Should we follow a
4procedure like the one Oscar implemented? If not: Can we do something which
5helps a bit and does not involve too much work? Or should we better do nothing?
6
7(a) Calculate, for each satellite, the STD of the code multipath in the
8iono-free combination Pc, as a combination the carrier phase and the code.
9Do this continuously, using a circular register that contains the observations
10of the previous 10 minutes.
11(b) Introduce a default STD that is used when, either at the beginning or
12after an interruption in the data, there is less than 10 minutes worth of
13data for finding the multipath STD as in (1), and the STD with insufficient
14data is less than this default.
15(c) Introduce use a "fudge factor" to multiply the data-based STD and get the
16actual value used to get the data. This is necessary, because the correct weight
17of the data depends on numerous factors, particularly the weights assigned to
18the phase and to the a priori values of the unknowns. This problem also is true
19for (b), (c), and (d). So the fudge factor really depends on the overall strategy
20and cannot be used in different software implementations.
21Everyone has to find it the hard way, by trial and error, making lots of solutions.
22(The variance of unit weight is of very limited help for this purpose.)
23(d) Downweight the code by a large factor when a satellite is below 20 degrees
24in elevation, or the 3-D precision of the coordinates being estimated falls
25below something like 25 cm (again, this will be a different threshold with
26different software).
27
28(2) NMEA GGA string is not fully compatible with the standard.
29The following are observations by Tamas Horvath:
30(a) Time tag should refer to UTC time and not GPS system time.
31(b) Time tag format is hhmmss.ss and not hhmmss.
32(c) The GPS Quality indicator field is 1 (GPS SPS Mode), which is correct, as
33there is no category for PPP. In my opinion the NMEA protocol should be
34extended by a new indicator number for PPP to make a clear difference between
35autonomous GNSS and PPP.
36(d) The HDOP value is constantly 2.0, which is obviously not real. I think this
37field is filled with 2.0 as a default value in BNC.
38(e) The Age of Differential GPS data field is not populated. I believe here the
39age of RTCM SSR data should be put.
40
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