Methods for GNSS measurement

Since the 1980s, several methods and techniques for GNSS surveying have been developed and the development is still ongoing. The use of GNSS surveying constantly opens new areas of application, both in research and commercial activities.

The basic principles of all GNSS surveying

All GNSS surveying is based on the same basic principles:

  • GNSS surveying requires a clear line of sight between receivers and satellites.
  • A GNSS receiver determines the distance between receivers and satellites using code measurement and/or carrier phase measurement on the GNSS signal. See also a brief comparison of code and carrier phase measurements. Based on the distances to at least four satellites, the receiver then calculates its position.
  • GNSS surveying has a number of sources of error that affect the uncertainty of calculated positions. Using so-called overdetermination by measuring against more than four satellites and by trying to estimate or model the impact of the sources of error on the satellite signals, you can reduce the uncertainty in the receiver's calculated positions.
  • GNSS surveying can also be carried out with one or more GNSS receivers. Surveying with one receiver is called absolute positioning. If you are using more than one receiver, you can have some of them measure over points with an already known position. These receivers are called reference receivers and the measurement method is called relative positioning.

Methods for accurate geodetic GNSS surveying

Accurate geodetic surveying with GNSS enables a standard uncertainty of a few centimetres in calculated positions and is today almost exclusively done with relative carrier phase measurements. The position van be calculate either in real time using RTK technology or by post-processing.

Ground-based GNSS infrastructure, such as SWEPOS, is a common way to collect and exploit information from a network of permanent GNSS receivers for accurate relative positioning. Such infrastructure enables positioning services based on network RTK technology and can facilitate or improve positioning for you by eliminating the need to set up your own reference receivers at points with known positions.

However, even if you only have direct access to information from your own receiver, you can still reduce the impact of certain sources of error by adding external information about these sources of error with accurate absolute positioning. This measurement method is called Precise Point Positioning.

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