三维激光标靶球球心整体最小二乘拟合方法研究

通过分析整体最小二乘球心拟合算法及其在三维激光标靶球球心拟合中计算量较大的问题,提出了在保证球心精度不变的基础上尽可能减少多余球面点的方法,以加快TLS球心拟合算法的运算速度。针对TLS构建的大型稀疏矩阵,采用大型稀疏矩阵快速乘法计算法方程系数矩阵,大大减少了TLS拟合球心所消耗的时间。通过试验分析表明:对多余球面点进行适当过滤既可以保证球心坐标精度又可以加快球心拟合速度;采用大型稀疏矩阵快速乘法可以大大缩短TLS球心拟合的时间。

圆形隧道断面检测数据拟合新方法

针对圆形隧道断面检测数据拟合算法存在的不足,提出一种新的数据拟合算法。该算法首先对所有的观测点进行平面拟合,而后将所有的观测点进行球壳拟合,该球壳的球心必须位于拟合的平面内,并且在拟合的流程中加入粗差检验。该方法避免了坐标投影、坐标转换、迭代计算等复杂操作,可以直接得到空间圆的圆心、半径等参数。该模型可靠,拟合精度高,实现简便,节省计算资源,是一种良好的圆形隧道断面拟合算法。

一种评定最小二乘球的优化算法

提出一种评定最小二乘球的优化算法，其基本思想是利用最小二乘球线性简化模型的迭代运算去逼近最小二乘球非线性精确模型的优化解。算法具有收敛速度快、寻优精度高的优点，适用于球、半球和球冠的参数拟合及其形状误差的评定。

基于俯仰轴相交和球拟合的天线旋转中心测量方法

针对传统天线旋转中心测量时,俯仰轴生成方式不严密对其精度和可靠性产生不利影响的问题,提出了俯仰轴相交和球拟合两种新的旋转中心测量方法。对不同方位下标志点绕俯仰轴的运动轨迹进行圆拟合,得到含有方位信息的俯仰轴,多条俯仰轴求交点作为旋转中心,称之为俯仰轴相交法,较传统方法可靠性更高。对标志点的运动轨迹进行球拟合,取所有球心的均值作为旋转中心,称之为球拟合法,避免了圆拟合及求交点的过程,方法更为严密。以3台φ3 m上行阵天线为实验对象,应用全站仪和工业摄影测量技术获取标志点在规划姿态下的坐标,采用两种新方法处理观测数据,均得到了内符合精度达亚毫米级的旋转中心。

面向结构光三维测量的两轴转台标定

提出了一种基于结构光测量数据的两轴转台标定新方法.在转台绕摆动轴转动过程中对按一定布局固定在转台上的2个标定球进行不同视角测量,通过数据分割得到每个球的数据并计算其球心,采用2个标定球球心所在圆的圆心精确标定了转台摆动轴轴线;同理,可以标定出转动轴的初始轴线.通过计算得到转动轴在任意视角的方位,从而精确标定了两轴转台的位姿,实现了多视测量数据在线自动拼合,提高了数据拼合的精度.实验证明,所提出的标定方法简单、高效,并适用于其他转台测量系统.

GGOS对流层延迟产品精度分析及在PPP中的应用

对流层延迟是卫星导航定位的主要误差源,GNSS广域增强需要高精度的对流层延迟产品进行误差修正。对流层延迟可通过GNSS进行实时估计,也可通过融合多源数据的数值气象预报模型获取。IGS发布的全球对流层天顶延迟产品由GNSS解算,其精度可达4mm,时间分辨率为5min,但其分布不均匀,在广袤的海洋区域无数据覆盖。GGOS Atmosphere基于ECMWF 40年再分析资料,可提供1979年以来时间分辨率为6h、空间分辨率为2.5°×2°的全球天顶对流层总延迟格网数据。本文通过2015年全球IGS测站的ZTD资料对GGOS的ZTD产品进行了评估,研究了GGOS Atmosphere对流层延迟产品与IGS发布ZTD资料之间的系统差,通过线性拟合估计出每个测站GGOS-ZTD与IGSZTD系统差系数(包括比例误差a和固定误差b),然后对比例误差a、固定误差b进行球谐展开,建立了两种ZTD数据源之间的系统差模型。选取IGS测站和陆态网测站,对附加系统偏差改正后的GGOSZTD产品对PPP的收敛速度的影响进行研究。本文研究结果表明:GGOS-ZTD与IGS-ZTD间存在系统偏差,其bias平均为-0.54cm;两者之间较差的RMS平均为1.31cm,说明GGOS-ZTD产品足以满足广大GNSS导航定位用户对对流层延迟改正的需要。将改正了系统差后的GGOS-ZTD产品用于ALBH、DEAR、ISPA测站、PALM测站、ADIS测站、YNMH测站、WUHN测站进行PPP试验,发现可明显提高定位收敛速度,尤其是在U方向上,收敛速度分别提高10.58%、31.68%、15.96%、43.89%、51.46%、14.69%、18.40%。

MetroIn在大尺寸天线罩安装测量中的应用

阐述大尺寸天线罩的高精度安装测量方案,基于MetroIn工业测量软件平台对测量数据进行处理和分析,全方位实时指导天线罩的现场安装。通过对一台口径为5m的天线进行防护罩安装测量,验证方案的正确性,表明其理论和技术成功可行。

Prosthetic modeling for femoral head based on ellipsoid fitting

A novel modeling method which can restore the shape of the femoral head with collapse induced by ischemic necrosis is proposed. First, sequential tomograms of the hip are obtained from a CT scan; secondly, an accurate and automatic method is used to extract the profile of the acetabulum; thirdly, a hybrid method is utilized to gather fiducial marks on the acetabulum; fourthly, bulky error sampling points are removed. Finally, an ellipsoid fitting method is used to fit the ellipsoid model of the femoral head. Two male sufferers with different necrosis extents are chosen as experimental subjects for contrastive simulation. Fifty cases of different ages （from 25 to 79 years old） are utilized for statistical comparisons of matching errors. The prosthetic models highly resemble the primary shape of the femoral head in health. This new method provides not only a theoretical model for accurate operation position fixing in an orthopaedics clinic, but it is also an innovative practical means for the individual manufacture of artificial femoral heads.

一种基于向量的空间圆检测方法

提出一种新的空间圆检测方法。首先以观测点拟合平面,然后采用空间向量构成中垂面的方法拟合球壳,并加入圆心在拟合平面内的限制条件,直接解算空间圆的圆心坐标及半径;同时在拟合过程中加入粗差剔除。该方法的数学模型可靠、拟合精度高,相比其他拟合方法,其实现更加简便。

Mensi激光扫描仪精度测试方法研究

本文报道了一种新颖的激光扫描仪精度测试方法。采用室内双频激光干涉仪为计量标准,建立了一条高精度室内基线。以扫描仪的定向球作为测量目标,通过对球面拟合获得其球心,以此作为间接测量点,并统计建模前的点位精度。将多个间接测量点与室内基线进行比对,得到了建模后的点位精度,并检验出了扫描仪的尺度因子。合成建模前的点位精度和建模后的点位精度,即为扫描仪的综合点位精度。将本文的研究成果进行拓展,即可应用于其它类型扫描仪的精度测试。

坐标测量机校准中三维探测误差的计算方法的探讨

三坐标测量机是20世纪60年代发展起来的一种新型、高效、多功能的精密测量仪器。对于坐标测量机校准和性能评价中,其中最大允许探测误差(M PEP)是一项重要指标。文章对探测误差的计算方法从一种常见的数学模型出发,探讨具体的算法、数学原理以及实现该方法的过程。为从事该项目校准的人员提供理论和实践的参考。

Converting GPS height by a new method based on neural networks

The adjusted GPS height is the height above the surface of the WGS-84ellipsoid. It is necessary to convert a GPS height into a normal height in engineering. The conicoidfitting method (CFM) and the neural networks method (NNM) are used for this purpose, but each ofthem has its advantages and disadvantages. After studying these two methods, a new method (abbr.CF&NNM) is conceived. The procedure of the CF&NNM is introduced. A practical engineering example isused to study these three different methods. The results by the three methods are listed. The CF&NNMmethod can produce better results than either the CFM or the NNM in deriving normal height from GPSheight. The theory of the CF&NNM method is analyzed.

Glacier Changes during the Past 40 Years in the West Kunlun Shan

Recent studies on glaciers in the West Kunlun Shan, northwest Tibetan Plateau, have shown that they may be stable or retreating slightly. Here, we assess changes in the mass of the glaciers in the West Kunlun Shan(WKS) in an attempt to understand the processes that control their behavior. Glaciers over the recent 40 years(1970-2010) have shrunk 3.4±3.1%in area, based on a comparison between two Chinese glacier inventories. Variations of surface elevations, derived from ICESat-GLAS(Ice, Cloud, and Land Elevation Satellite-Geoscience Laser Altimeter System) elevation products(GLA14 data) using the robust linear-fit method, indicate that the glaciers have been gaining mass at a rate of 0.23±0.24 m w.e./a since 2003. The annual mass budget for the whole WKS range from 2003 to 2009 is estimated to be 0.71±0.62 Gt/a. This gain trend is confirmed by MOD10A1 albedo for the WKS region which shows a descent of the mean snowline altitude from 2003 to 2009.

Numerical Simulation of Viscous Flow Through Spherical Particle Assemblage with the Modified Cell Model

The cell model developed since 1950s is a useful tool forexploring the behavior of particle assemblages, but it demandsfurther careful development of the outer boundary conditions so thatinteraction in a particle swarm is better represented. In this paper,the cell model and its development were reviewed, and themodifications of outer cell boundary conditions were suggested. Atthe cell outer boundary, the restriction of uniform liquid flow wasremoved in our simulation conducted in the reference frame fixed withthe particle.

Optimization of multi-revolution low-thrust transfer based on modified direct method

A modified direct optimization method is proposed to solve the optimal multi-revolution transfer with low-thrust between Earth-orbits. First, through parameterizing the control steering angles by costate variables, the search space of free parameters has been decreased. Then, in order to obtain the global optimal solution effectively and robustly, the simulated annealing and penalty function strategies were used to handle the constraints, and a GA/SQP hybrid optimization algorithm was utilized to solve the parameter optimization problem, in which, a feasible suboptimal solution obtained by GA was submitted as an initial parameter set to SQP for refinement. Comparing to the classical direct method, this novel method has fewer free parameters, needs not initial guesses, and has higher computation precision. An optimal-fuel transfer problem from LEO to GEO was taken as an example to validate the proposed approach. The results of simulation indicate that our approach is available to solve the problem of optimal muhi-revolution transfer between Earth-orbits.

Along Road Height Interpolation Based on Discrete Elevation Points

The simulating exactly compared with realty of ground surface to run a model is more and more highly required. In the real, terrain of the earth surface is always complicated by the natural and human made ground objects. Because of limitation of collecting and storing technologies in the past time, data are usually not detailed so that the data can not be full for the simulation. Besides computing power and simulation increase more day by day, the increasing requirements more detailed of topography surface simulation is a demand. In simulated flooding phenomenon or phenomena related to energy and momentum of water flow, the linear objects of ground surface such as roads, dikes, dams, etc. need to have their vertical dimension along continuously. However, these datas have often no height information alternately, there are only discrete elevation points that are extracted from topographic maps. Consequently, the demand of a suitable method for linear objects height interpolation is necessary. This paper aims to provide a method and evaluate its accuracy to meet this requirement.

Seismic to Reservoir Simulation by Cooperative Inversion

Cooperative inversion for petroleum reservoir characterization produces an Earth model that fits all available geological, geophysical and reservoir production data to within acceptable error criteria. The mathematical formulation for the inversion requires an appropriate modeling description of both seismic wave propagation and reservoir fluid flow. The inversion requires the minimization of an objective function which is the weighted sum of model misfits for both geophysical and production data. While the complete automation of cooperative inversion may be unrealistic or intractable, geophysical data can provide useful information for enhancing heavy oil production. A methodology is given to demonstrate possible cooperative inversion application in heavy oil reservoirs.

Impacts of internal climate variability on meteorological drought changes in China

Drought is one of the extreme events that can be caused by internal climate variability （ICV） and external forcing （EF）. Here, the authors investigate the relative contributions of ICY and EF to meteorological drought changes in China using 40 members from the Community Earth System Model Large Ensemble （CESE_LE） project for historical simulations （in response to greenhouse gases and other EF） and future simulations under the RCP8.5 scenario. The authors use the Standardized Precipitation Index （SPI） to represent meteorological drought, and then define and analyze four drought parameters （frequency, severity, duration, and maximum duration） over eight regions of China. For historical periods, the ICV plays a dominant role in drought variation, while with global warming under the RCP8.5 scenario the EF becomes the prominent factor for drought characteristics. With the global warming signal, the effect of ICV varies with the drought parameters. This study suggests that the ICV should be taken into account when climate model simulations are used to investigate drought--in particular, for historical periods.

Process Optimization of Cu-en/AP Composite Microspheres Preparation by Electrostatic Spray Method Based on ANSYS Simulation

To investigate the process optimizationof Cu-en/AP composite microspheres preparation via electrostatic spraying,and to reveal the effects of droplet properties and flow rate variations on the experimental results during the electrostatic spraying process,the prepared process parameters of Cu-en/AP composite microspheres by electrostatic spray method under the orthogonal experimental design simulated by ANSYS(Fluent).The influence of flow rate,solvent ratio,and solid mass on the experimental results is examined using a controlled variable method.The results indicate that under the conditions of a flow rate of 2.67×10^(-3)kg/s an acetone-to-deionized water ratio of 1.5∶1.0,and a solid mass of 200 mg,the theoretical particle size of the composite microspheres can reach e nanoscale.Droplet trajectories in the electric field remain stable without significant deviation.The simulation results show that particle diameter decreases with increasing flow rate,with the trend leveling off around a flow rate of 1×10^(-3)kg/s.As the solvent ratio increases(with higher acetone content),particle diameter initially decreases,reaching a minimum around a ratio of 1.5∶1.0 before gradually increasing.Increasing the solid mass also reduces the particle diameter,with a linear increase in diameter observed at around 220 mg.Cu-en/AP composite microspheres with nanoscale dimensions were confirmed under these conditions by the final SEM images.

Orbit Fitting Based on Helmert Transformation

Orbit fitting is used in many GPS applications. For example, in Precise Point Positioning (PPP), GPS orbits (SP3 orbits) are normally retrieved either from IGS or from one of its Analysis Centers (ACs) with 15 minutes’ sampling, which is much bigger than the normal observation sampling. Therefore, algorithms should be derived to fit GPS orbits to the observation time. Many methods based on interpolation were developed. Using these methods the orbits fit well at the sampling points. However, these methods ignore the physical motion model of GPS satellites. Therefore, the trajectories may not fit the true orbits at the periods in between 2 sampling epochs. To solve this problem, we develop a dynamic approach, in which a model based on Helmert transformation is developed in GPS orbit fitting. In this orbit fitting approach, GPS orbits at sampling points are treated as pseudo-observations. Thereafter, Helmert transformation is built up between the pseudo-observations and dynamically integrated orbits at each epoch. A set of Helmert parameters together with corrections of GPS initial orbits are then modeled as unknown parameters. Results show that the final fit orbits have the same precision as the IGS final orbits.