Dear GPS Developers<div><br></div><div>I am a Ph.D student working on real-time GPS algorithms. Currently I have a problem about the reference satellite selection.</div><div><br></div><div>As we know, most of the RTK algorithm choose the highest elevation satellite as reference satellite, but when the baseline is quite long(eg. network-rtk), it may take quite long time (may be more than half hours) to get the ambiguity initialized, and during the initialization we don't want the reference satellite changes, otherwise we may need to restart the initialization. </div>
<div><br></div><div>So if at the very beginning, we could find the longest session satellite as the reference satellite, it will help us to guarantee the reference satellite will not change before the initialization finished. I read GPStk's source code of "vecsol", it give a solution of project the satellite's velocity "V" to the U direction of the local NEU coordinate "Vu", and take the biggest "Vu" satellite as the reference satellite. I check this method and find it indeed give us a longer session satellite, however, when I check this method for all the available satellite at that epoch, It doesn't conclude that "the bigger the Vu, the longer the following observed session". </div>
<div><br></div><div>I am very interested in this method because It's easy to implement and can be use in real-time algorithm. So I am wondering if someone can explain this method in a mathematical way, or give a better solution.</div>
<div><br></div><div>Thanks in advance.</div><div><br></div><div>Regards.</div><div><br></div><div>Shaocheng Zhang</div><div>School of Geodesy and Geomatics, Wuhan University, P.R.China</div><div>Email: <a href="mailto:gnss.zhangsc@gmail.com">gnss.zhangsc@gmail.com</a></div>