Tuesday, August 11, 2020

GP, BD, SB, and other satellite annotations in cgps/xgps gpsd service

Sometimes I stumble onto a problem and Google really has no idea what I'm asking about.

In my case it's the 2-letter satellite code in the CGPS/XGPS program. What are these 2-letter symbols and what do they represent? They are different satellite-based radionavigation (RNSS) identification codes.

Below is the output from cgps, a terminal GUI for the gpsd software I currently have running on my stratum-1 raspberry pi NTP timeserver:

Not my real GPS coordinates :-)

Here's what those two-letter satellite codes mean:

The GPS system that everyone knows and loves started (like many pieces of technology) as a military research project. In its early days it was used to track nuclear-capable subs, and was later expanded by the DOD to be a general purpose navigation system[1].

Now GPS is used worldwide for virtually all positioning applications. However, the satellites that power GPS are still largely under the control of the US government, and the things that are given can also be taken away.

As you can imagine the US hegemony of control is seen as a national security risk by other countries. Given that, some countries have launched their own competing technologies so as not to rely on a rival's generosity. The three largest alternatives to GPS are Russia's GLONASS, China's Beidou, and the EU's Galileo.

Here's a summary of these systems:

GPS/GNSS (United States) 🇺🇸
By far the most widely-used navigation system. Originally developed for military use. Accurate down to 10 centimeters or less. This is the system you think of when you hear the word "GPS".

GLONASS (Russia) 🇷🇺
Competing technology designed in the 1970s by the USSR, now used throughout Russia.

BeiDou (China) 🇨🇳
Launched in 2000 as a rival to GPS. The positions of the satellites are said to make this system more accurate around Asia. China has 22 operational BeiDou satellites and is expected to continue to launch more and increase the coverage and accuracy of this system. Did you know that China uses datum displacement to intentionally obfuscate GNSS map accuracy? Read more here.

Galileo (EU) 🇪🇺
Launched in 2011 by the European Union. Galileo currently operates 14 satellites and is intended to be more accurate at higher latitudes than GNSS systems such as GPS.

There are other systems as we the Indian Regional Navigation Satellite System (IRNSS). These systems are meant to improve the accurate and coverage of specific geographic locations (in this case India).