Online Positioning User Service (OPUS)—A data processing service run using National Geodetic Survey (NGS) computers and software. Users send in GPS data in RINEX file format, and NGS processes the data with respect to the three best CORS sites available and returns a position to the user.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

Part of LearnCST’s exam text bundle.