Support RTCM-SSR to SPARTN

[y3nd]

Hello,
I know the title may seem a bit strange but I think the idea is worth a try.

The CNES (a french space agency) is providing free SSR streams to the scientific community and general public through the PPP-WIZARD project http://www.ppp-wizard.net/. They announce sub-30 sec convergence with sub-decimeter accuracy worldwide.

The SSR streams are encoded with RTCM-SSR messages that cannot be interpreted by common receivers, which only use RTCM-OSR (legacy/MSM4/MSM7 messages), provided by a real RTK base. Common SSR/RTK providers use Geo++ software suites to both create a SSR model from a RTK base network and distribute the correction streams in RTCM-SSR, SPARTN (formerly SAPA) and RTCM-OSR for compatibility with all receivers.

SSR to OSR seems very complicated to do, at least it is not just copying data from a format to another, and it is one of the main modules of the Geo++ suite. There are multiple solutions available but not a single one with RTCM-OSR message generation :
https://github.com/GeoppGmbH/RTCM-SSR-Python-Demonstrator
https://github.com/QZSS-Strategy-Office/claslib
https://github.com/tomojitakasu/RTKLIB

PPL/PointPerfectLibrary/libpointperfect, formerly SAPALIB, provides SPARTN (SSR) to RTCM (OSR), so basically a VRS service that can bridge the gap between SPARTN and legacy receivers. The library is used by the PointPerfect service to provide RTCM-OSR streams based on the position in the rover-sent GxGGA message.
arm
https://github.com/septentrio-gnss/uBloxCorrectionsWithSeptentrio/tree/main/ssnppl_demonstrator/raspberry-build
xtensa
https://github.com/sparkfun/SparkFun_u-blox_PointPerfect_Library/tree/main/src

So, by building an SSR (RTCM-SSR) to SSR (SPARTN) converter, we could provide worldwide corrections to SPARTN-compatible receivers (ublox only for now...). Then, using PPL, we could provide these corrections to any RTCM-compatible receivers.

[semuadmin]

Hi @y3nd

Unfortunately I don't think I'll have the time to look into this, but happy to consider contributions.

If the CNES SSR message definitions are available in the public domain, the pyrtcm library can be updated to include the RTCM-SSR messages, assuming they conform to the general RTCM3 transport specification, but I think that would only go half way to meeting your requirement.