{"id":4416,"date":"2017-12-11T20:21:54","date_gmt":"2017-12-11T20:21:54","guid":{"rendered":"https:\/\/www.use-snip.com\/kb\/?post_type=ht_kb&p=4416"},"modified":"2019-11-25T00:34:30","modified_gmt":"2019-11-25T00:34:30","slug":"orbit-and-clock-corrections-feeds","status":"publish","type":"ht_kb","link":"https:\/\/www.use-snip.com\/kb\/knowledge-base\/orbit-and-clock-corrections-feeds\/","title":{"rendered":"Orbit and Clock corrections feeds"},"content":{"rendered":"

The number of SNIP<\/strong><\/span> users, both SNIP<\/strong><\/span> Caster<\/a> operators, and those connecting to SNIP<\/strong><\/span> nodes with NTRIP Clients<\/a>, have been asking about orbital and clock corrections (the so called ‘State Space Representation’ (SSR) messages found in RTCM 3.3 messages<\/a> and beyond).\u00a0 SNIP<\/strong><\/span> handles every defined and adopted SSR message, as well as those still in the experiential range and those send in proprietary message assignments.\u00a0\u00a0 If you wish to send any non-standardized messages, simply disable parsing<\/a> and send the message using the bent-pipe<\/a> mode.<\/p>\n

This article discusses how to set orbital and clock corrections up on your own copy of SNIP<\/strong><\/span> or how to get them from either NTRIP.use-snip.com or from the RTK2go.com<\/strong><\/span><\/a> open Caster. If you also need a source for a broadcast ephemeris<\/span> stream, you can connect to the RTCM3EPH<\/strong> stream for that content.<\/p>\n

Aside<\/strong><\/span>: It is typical to connect to a RTCM3EPH<\/strong> stream once just after rover power-up (to obtain the data quickly) and then disconnect.\u00a0 Long term connections can put a usage cost on cellular links to be avoided. The same data is transmitted for long periods without any change until the orbital update (~2hr GPS, ~30min GLO, etc.).<\/p>\n

Corrections to Broadcast Ephemerides<\/span> and Clocks, background<\/h3>\n

The basic format for sending clock offset and drifts and describing the orbital data for each GPS space vehicle (SV) was developed over 35 years ago.\u00a0 Times (and politics) have changed and we now provide much more accurate data than the original message definition allowed.\u00a0 Many of the firms with claims along the lines of “download our orbital data and use them for 2 weeks with better accuracy<\/em>” exploit this fact.\u00a0 Other aspects of the problem (clock drifts and walks) can be bounded but cannot be predicted, hence a semi real time data link is wanted.<\/p>\n

\"\"<\/a>Thankfully we have IGS<\/strong> <\/a>to save the day and provide the entire world with various data products in several ready-to-use formats.<\/p>\n

To use their own words about this wonderful and vital group:\u00a0\u00a0 Mission<\/a><\/p>\n

The International GNSS Service provides, on an openly available basis, the highest-quality GNSS data, products and services in support of the terrestrial reference frame, Earth observation and research; positioning, navigation and timing; and other applications that benefit science and society.\u00a0 To learn more about the IGS Mission, and how it is benefitting society, please refer to the IGS Strategic Plan<\/a>, and the IGS Progress Report<\/a>.<\/p>\n

These two articles provide a very good job of explaining the issues and mention which RTCM message are used for various needs.\u00a0 Keep in mind that you need to be sure what reference frame is being used with the different orbital data feeds as well.<\/p>\n