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GNSS positioning calculation : ウィキペディア英語版
GNSS positioning calculation

The global navigation satellite system (GNSS) positioning for receiver's position is derived through the calculation steps, or algorithm, given below.
In essence, a GNSS receiver measures the transmitting time of GNSS signals emitted from four or more GNSS satellites and these measurements are used to obtain its position (i.e., spatial coordinates) and reception time.
==Calculation steps==
# A global-navigation-satellite-system (GNSS) receiver measures the apparent transmitting time, \scriptstyle \tilde_i, or "phase", of GNSS signals emitted from four or more GNSS satellites (\scriptstyle i \;=\; 1,\, 2,\, 3,\, 4,\, ..,\, n ), simultaneously.〔Misra, P. and Enge, P., Global Positioning System: Signals, Measurements, and Performance, 2nd, Ganga-Jamuna Press, 2006.〕
# GNSS satellites broadcast the messages of satellites' ephemeris, \scriptstyle \boldsymbol_i (t), and intrinsic clock bias (i.e., clock advance), \scriptstyle\delta t_ (t) as the functions of (atomic) standard time, e.g., GPST.〔(The interface specification of NAVSTAR GLOBAL POSITIONING SYSTEM )〕
# The transmitting time of GNSS satellite signals, \scriptstyle t_i, is thus derived from the non-closed-form equations \scriptstyle \tilde_i \;=\; t_i \,+\, \delta t_ (t_i) and \scriptstyle \delta t_ (t_i) \;=\; \delta t_ (t_i) \,+\, \delta t_ (\boldsymbol_i,\, \dot,i} (\boldsymbol_i,\, \dot_i \;=\; \boldsymbol_i (t_i) and \scriptstyle \dot}_i (t_i).
# In the field of GNSS, "geometric range", \scriptstyle r(\boldsymbol_A,\, \boldsymbol_B) , is defined as straight range, or 3-dimensional distance,〔3-dimensional distance is given by \scriptstyle r(\boldsymbol_A,\, \boldsymbol_B) = |\boldsymbol_A - \boldsymbol_B| = \sqrt where \scriptstyle\boldsymbol_A = (x_A, y_A, z_A) and \scriptstyle\boldsymbol_B = (x_B, y_B, z_B) represented in inertial frame.〕 from \scriptstyle\boldsymbol_A to \scriptstyle\boldsymbol_B in inertial frame (e.g., Earth Centered Inertial (ECI) one), not in rotating frame.〔
# The receiver's position, \scriptstyle \boldsymbol_}, satisfy the light-cone equation of \scriptstyle r(\boldsymbol_i,\, \boldsymbol_}) \;=\; 0 in inertial frame, where \scriptstyle c is the speed of light. The signal transit time is \scriptstyle -(t_i \,-\, t__i,\, \boldsymbol_}) \,+\, \delta t_ \,-\, \delta t_ \;=\; 0 , where \scriptstyle \delta t_ is atmospheric delay (= ionospheric delay + tropospheric delay) along signal path and \scriptstyle \delta t_ is the measurement error.
# The Gauss–Newton method can be used to solve the nonlinear least-squares problem for the solution: \scriptstyle (\hat},\, \hat__} ), where \scriptstyle \phi ( \boldsymbol_} ) \;=\; \sum_^n ( \delta t_ / \sigma_ } )^2 . Note that \scriptstyle \delta t_ should be regarded as a function of \scriptstyle \boldsymbol_}.




# The posterior distribution of \scriptstyle \boldsymbol_} is proportional to \scriptstyle \exp ( -\frac \phi ( \boldsymbol_} ) ), whose mode is \scriptstyle (\hat},\, \hat__^\infty \exp ( -\frac \phi ( \boldsymbol_} ) ) \, d t_{\text{rec}}.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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