The recently developed integrated Precise Point Positioning (PPP) GPS/INS system can be useful to many applications, such as UAV navigation systems, land vehicle/machine automation and mobile mapping systems. Since carrier phase measurements are the primary observables in PPP GPS, cycle slips, which often occur due to high dynamics, signal obstructions and low satellite elevation, must be detected and repaired in order to ensure the navigation performance. In this research, a new algorithm of cycle slip detection and identification has been developed. With the aiding from INS, the proposed method jointly uses WL and EWL phase combinations to uniquely determine cycle slips in the L1 and L2 frequencies. To verify the efficiency of the algorithm, both tactical-grade and consumer-grade IMUs are tested by using a real dataset collected from two field tests. The results indicate that the proposed algorithm can efficiently detect and identify the cycle slips and subsequently improve the navigation performance of the integrated system.
Suprachoroidal hemorrhage (SCH) is a rare but serious sight-threatening complication of inner eye surgery. Despite continuous advances in treatment, visual prognosis remains poor. The disease has a more typical clinical presentation, the etiology and pathogenesis are not well defined, and intraoperative ocular and systemic factors may induce fulminant SCH. To investigate risk factors and treatments of SCH-associated intraocular surgeries, summarize diagnosis, characteristics, management, and prevention of SCH developed during and after intraocular surgeries. A retrospective study of SCH occurred in six cases of intraocular surgeries including cataract, glaucoma, pars plana vitrectomy (PPV), and silicone oil removal surgery. Assess baseline systemic and ocular characteristics of SCH eyes. Analyze the second surgery timing and technique, and visual outcomes were measured. SCH occurred in six patients including five eyes during surgeries and one eye after the surgery. Three eyes that underwent cataract surgery had hard nucleuses (nuclear sclerotic 4+). One eye was due to hypotony during the vitrectomy procedure. One eye developed SCH when silicone oil was extracted from the eyeball. One eye developed delayed SCH after glaucoma surgery. Incision closure and anterior chamber deepening were performed. B-scan ultrasonography was used to diagnose SCH, and determine the timing and location of sclerotomy for the second surgery. Vitrectomy and sclerotomy were performed in five eyes. The median follow-up time was six months. The final best-corrected visual acuity (BCVA) was 0.3 in one eye, one eye had light perception with retinal adherence, and four eyes had no light perception with retinal detachment. The results showed that risk factors including advanced age, hypertension, taking anticoagulants, antiplatelet drugs, and cardiovascular drugs were systemic risk factors, and hard nucleus (nuclear sclerosis 4 +) cataract, long-term uncontrolled ocular hypertension glaucoma, vitrectomy, silicone oil removal, high myopia, aphakia, previous intraocular surgery, intraocular pressure during surgery, and others were ocular risk factors. The most important risk factor is a sudden drop in intraocular pressure during or after surgery. The outcome of visual acuity depends on retinal status. Because of the poor prognosis, the prevention of SCH is of utmost importance during intraocular surgery.
The BeiDou system has been providing a regional navigation service since 27 December 2012. The Global Navigation Satellite System (GNSS) user community will benefit from combined Global Positioning System (GPS)/BeiDou positioning due to improved positioning accuracy, reliability and availability. But to achieve the best positioning solutions, precise weights of the GPS and BeiDou observations are important since this involves the processing of measurements from two different satellite systems with different quality. Currently, a priori variances are typically used to determine the weights of different types of observations. However, such an approach may not be precise since many un-modelled errors are not accounted for. The Helmert variance component estimation method is more appropriate in this case to determine the weights of GPS and BeiDou observations. This requires high redundant observations in order to obtain reliable solutions, which will be a concern in the case of insufficient numbers of visible satellites. To address this issue, a weighting approach is proposed by a combination of the Helmert method and a moving-window average filter. In this approach, the filter is applied to combine all epoch-by-epoch weight estimates within a time window. As a result, more precise and reliable weights for GPS and BeiDou observations can be obtained at every epoch. Both static and kinematic tests in open sky and under tree environments are conducted to assess the performance of the new weighting approach. The results indicate significantly improved positioning accuracy. K E Y
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