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Positioning Methods
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
In addition, UNB’s PPPSC (Precise Point Positioning Software Centre) compares solutions from online PPP applications (http://www2.unb.ca/gge/Resources/PPP). All of the aforesaid systems support RINEX format, and the online processing services provide the coordinates in a recognised datum. However, it should be mentioned that while producing these coordinates, all services depend on the quality of the data and the length of data span supplied to them by the user (Tsakiri 2008). Generally, these services produce coordinates in the ITRF or their national geodetic reference frame. Transformation of coordinates is possible from one reference frame to another, either using the published transformation parameters or available online software from governmental organisations, such as NGS Coordinate Conversion and Transformation Tool (https://www.ngs.noaa.gov/NCAT).
Rotational Sequences and Quaternion
Published in Yaguang Yang, Spacecraft Modeling, Attitude Determination, and Control Quaternion-based Approach, 2019
Like the Earth Centered Inertial (ECI) frame, the Earth-centered Earth-fixed (ECEF) frame is the Earth-based frame. The ECI frame is independent from the motion and the rotation of the Earth. However, it may not be convenient in some case as observatories on the ground rotate with the Earth. The center of ECEF frame is the center of the Earth. Using the convention adopted at the International Meridian Conference in Washington D.C. 1884, the primary meridian for the Earth is the meridian that the Royal Observatory at Greenwich lies on. The XECEF is the direction from the center of the Earth pointing towards the cross point of the primary meridian and equator. The ZECEF is the direction from the center of the Earth pointing towards the north pole. The YECEF is the direction that follows the right-hand rule. The ECEF frame is sometimes called International Terrestrial Reference Frame (ITRF). Due to the plate tectonic motion, the frame may need some adjustment every year for certain applications.
Satellite positioning
Published in W. Schofield, M. Breach, Engineering Surveying, 2007
It can be seen from the above statements that constant monitoring of the WGS84 system is necessary to maintain its validity. In 1997, 13 tracking stations situated throughout the globe had their positional accuracies redefined to an accuracy of better than 5 cm, thereby bringing the origin, orientation and scale of the system to within the accuracy of its theoretical specification. Another global datum almost identical to the WGS84 Reference System is the International Terrestrial Reference Frame (ITRF) produced by the International Earth Rotation Service (IERS) in Paris, France. The system was produced from the positional coordinates of over 500 stations throughout the world, fixed by a variety of geodetic space positioning techniques such as Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Doppler Ranging Integrated on Satellite (DORIS) and GPS. Combined with the constant monitoring of Earth rotation, crustal plate movement and polar motion, the IERS have established a very precise terrestrial reference frame, the latest version of which is the ITRF2000. This TRF has been established by the civil GPS community, not the US military. It comprises a list of Cartesian coordinates (X, Y, Z), with the change in position (dX, dY, dZ) in metres per year for each station. The ITRF2000 is available as a SINEX format text file from the IERS website. Details are at http://www.iers.org/iers/publications/tn/tn31/. The ITRF is the most accurate global TRF and for all purposes is identical to the WGS84 TRF. A new ITRF2005 is in preparation which will be based on the time series of station positions and earth orientation parameters using observations from at least 1999–2005.
Analysis on the differences between EOP 08C04 and EOP 14C04 related to the Earth rotation characteristics
Published in Journal of Spatial Science, 2022
Zhangzhen Sun, Tianhe Xu, Shi'e Zhou, Nan Jiang, Chunhua Jiang, Yuguo Yang
The IERS provides three types of products: International Celestial Reference Frame (ICRF), International Terrestrial Reference Frame (ITRF) and Earth Orientation Parameters (EOP). ITRF is the foundation for positioning services, satellite orbit determination and Earth science application. Since 1988, the IERS has released 13 versions of ITRF, among which ITRF2008 and ITRF2014 are commonly used. EOP 08C04 and EOP 14C04 were also released together with ITRF2008 and ITRF2014, respectively. Compared to previous ITRF versions, ITRF2014 is more stable and accurate (Altamimi et al. 2016).