I am performing a static PPP positioning and I have got the precise ephemeris from IGS rapid corrections. I got bad results compared to the satellite positions estimated by the NovAtel receiver which should not be the case. The precise data itself even before interpolation has around 300-1000 meter error compared to estimated position by receiver! What am I missing?
Check your PDOP. If it is too high (over 6) then you have to address this.
make sure you have enough satellites well dispersed and the area (site) is open (no obstruction by trees or others).
Let me know about total period of aquisition.
The result usually converge to a acceptable precision after two hours.
The data is two hours static but my problem is not about convergence yet. My problem is that the satellite position obtained from the precise ephemeris is different from the one calculated from the broadcast ephemeris by a range of 300 - 1000 meters !!! The one calculated from the broadcast ephemeris is giving me accuracy in the meter level as expected. The precise position is giving me much worse results. It seems like I am missing an operation that should be done to the precise data obtained from the IGS before it is used. (something rather than the interpolation)
Mohamed, i´ve been using the igr ephemeris directly as they are available in the IGS page and found nothing suspicous yet. If you want, send me your SV positioning results and will chek it, ok? By the way, did you already calculate your site position using some PPP oficial software?
@Mauro Menzori , Sorry for the late reply. I used an official software (inertial explorer) to calculate my site position as a reference. In the code, when you get the satellite position from IGS page, you need to interpolate it, compensate for Sagnac effect, right? Do you use a software for that or you do it on your own?
Dear Mohamed, i do not process PPP in separated parts. I´ve used the software available at Canadian Spatial Reference System (CSRS) page, for automatic processing.
I will try this software. However, in my research, I need to do the coding myself to be able to contribute to it later as I will integrate PPP with some other sensors
i hope i could help.
Interesting research you are developing. Let me know about the final results.
happy new year.
I really liked the online tool, but hope I will still develop my own code.
Thanks Mauro, happy new year for you too!
Now after spending time with PPP and its corrections, I can tell you guys what I have reached:
- when calculating the satellite position, correct for the signal transit time to know the correct signal transmission time
- when calculating the sat clk bias, correct also for relativity term
- Correct for the Sagnac effect
- Correct sat. position using sat. antenna sat phase center offsets in the IGS atx files.
- Correct for the antenna phase center offset if your reference receiver position is taken at antenna reference point
- Correct the for the code differential biases if exists (Ex: if you use C/A code for L1 and P2 code for L2, you have to correct using C1_P1 bias)
At least with this stage, you should reach centimeter-level in case of static scenarios. you can go for further precise corrections such as phase wind up, phase center variations, tidal effects ..etc
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