[FOSS-GPS] Required files/products for post-processed PPP

[Anders Wallin]

Hi, fwiw some notes from mostly using NRCan's gpsppp, just testing ESA gLAB
or rtklib once or twice. Receivers are dual-frequency so the ppp uses an
'ionosphere-free' linear combination - I don't have any experience with
ionosphere corrections for single frequency receivers.

For the clock and orbit products, note that there are many variants: final
(slow), rapid (1-2 days), and ultra-rapid (6h?) depending on what latency
you can tolerate. For me Rapid products seem to yield almost identical
results with Final producsts so I am using those. I haven't tried the
ultra-rapid products.
Also some datacenters have CLK and EPH files with 30s data interval (the
usual data interval in my RINEX files) but for long term storage they keep
only data with 300s interval, so when using these the CLK and EPH numbers
are interpolated - not sure about the effect on the position/time error.

ERP: earth-rotation-parameters, also from the IGS datacenter. Probably
these do not change rapidly so you are ok even if not using the latest file.

igs08.atx my understanding is that this contains the receiver antenna phase
center variations.

svb_gnss_yrly: satellite phase center variations?

OLC-file with ocean tide loading data in HARPOS format. afaik this is
modeled as a weighted sum of spherical harmonics. These change slowly so
you only need a new file maybe once a year. Onsala space obsevatory has a
site that outputs parameters if you input the coordinates of your antenna.

After all of these inputs it seems that the variation among ppp-flavours
(rtklib, gpsppp, ESA gLab, GIPSY, etc) is how they model troposhperic delay
ZTD. These parameters can also be adjusted but I haven't seen guidelines
for how to do it. I ran a comparison a while ago:
http://www.anderswallin.net/2013/12/comparing-gps-ppp-solutions/

The ppp-solution is a kind of digital filter, and many programs have the
option of running the filter both forward and backward on the time-series,
thus eliminating start/end transients. Not sure what is the best way to
combine the FWD and BCKW solutions into one. A popular option seems to be
to use teqc to concatenate many RINEX files into a long one, run the
ppp-solution, and then just discard transients at start and end.

Discussion/comments welcome!

Anders


On Sat, May 9, 2015 at 11:59 AM, Dimitris Psychas <psxdimitris at hotmail.com>
wrote:

> Hey everyone,
>
> I would like to ask about the required files that someone needs in order
> to estimate PPP solutions.
>
> Besides the precise orbit and clock products (sp3 and clk), observation
> and navigation files, is there any other file that someone should use for
> PPP estimation ? Is it mandatory to include ANTEX files (atx, pcv) for
> antenna phase center variations, or DCB files ?
>
> Afterwards, in the case of multi-GNSS post-processing PPP, MGEX has not
> published any MGEX ANTEX files, so is it fine if igs08.atx file is used
> within the processing ?
>
> Thank you in advance.
>
> Best regards,
> Dimitris Psychas
>
>
>
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