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function [xM,dtsvS,vMps,dtsvSDot] = GpsEph2Pvt(gpsEph,gpsTime)
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%[xM,dtsvS,vMps,dtsvSDot] = GpsEph2Pvt(gpsEph,gpsTime)
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%
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% Calculate sv coordinates, in ECEF frame, sv clock bias, and sv velocity
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% Inputs:
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% gpsEph: vector of ephemeris structures, as defined in ReadRinexEph.m
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%
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% gpsTime = [gpsWeek, ttxSec]: GPS time at time of transmission, ttx
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% ttx = trx - PR/c - dtsvS, where trx is time of reception (receiver clock),
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% dtsvS is the satellite clock error (seconds), can be computed in advance
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% using eph2dtsv.m or iterating this function: gps time = sat time - dtsvS
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% gpsWeek, ttxSec must be vectors of length(gpsEph),
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%
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% outputs:
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% xM = [i,j,k] matrix of coordinates of satellites (ecef meters)
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% dtsvS = vector of satellite clock error (seconds)
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% vMps = [i,j,k] matrix of satellite velocity (ecef m/s)
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% dtsvSDot = vector of satellite clock error rate (seconds/second)
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% The row dimension of xM, dtsvS, vMps, dtsvSDot = length(gpsEph)
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%
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% xM and vMps are the satellite positions and velocities
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% at time ttxSec, in terms of ecef coords at the same time
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% Use FlightTimeCorrection.m to get xM & vMps in ecef coord at time of reception
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%
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% functions called: GpsEph2Xyz.m
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%
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% See IS-GPS-200 for details of data
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%Author: Frank van Diggelen
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%Open Source code for processing Android GNSS Measurements
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vMps = []; dtsvSDot = [];
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[xM,dtsvS]=GpsEph2Xyz(gpsEph,gpsTime);
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if isempty(xM)
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return
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end
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%compute velocity from delta position & dtsvS at (t+0.5) - (t-0.5)
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%This is better than differentiating, because both the orbital and relativity
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%terms have nonlinearities that are not easily differentiable
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t1 = [gpsTime(:,1), gpsTime(:,2)+0.5]; %time + 0.5 seconds
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[xPlus,dtsvPlus] = GpsEph2Xyz(gpsEph,t1);
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t1 = [gpsTime(:,1), gpsTime(:,2)-0.5]; %time - 0.5 seconds
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[xMinus,dtsvMinus]= GpsEph2Xyz(gpsEph,t1);
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vMps = xPlus - xMinus;
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dtsvSDot = dtsvPlus - dtsvMinus;
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end %end of function GpsEph2Pvt
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% Copyright 2016 Google Inc.
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%
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% Licensed under the Apache License, Version 2.0 (the "License");
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% you may not use this file except in compliance with the License.
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% You may obtain a copy of the License at
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%
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% http://www.apache.org/licenses/LICENSE-2.0
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%
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% Unless required by applicable law or agreed to in writing, software
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% distributed under the License is distributed on an "AS IS" BASIS,
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% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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% See the License for the specific language governing permissions and
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% limitations under the License.
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