An enhanced bit-wise parallel algorithm for real-time GPS software receiver

Software-based global positioning system (GPS) receivers perform all the baseband signal processing and the high level functions on a general purpose processor. The heavy computational loads of the signal correlation in baseband processing make it difficult for software receivers to operate in real time. In order to improve the real-time performance, an enhanced bit-wise parallel algorithm has been developed in this study. The enhanced algorithm has been implemented and tested in a 12 channels real-time GPS software receiver. The system consists of a radio frequency front end, a data acquisition board and software that runs on a laptop with a Pentium-M 1.5 GHz processor running the Window^® XP operating system. The data acquisition board packs the 2-bit intermediate frequency samples with a 2-bit in/8-bit out shift register and transfers the packed samples to laptop through a USB port. The software running on the laptop performs all the baseband and navigation processing in real time. The test results show that the enhanced algorithm significantly improves the real-time performance of the software receiver by reducing the computational operations for signal correlation by 50% compared with the existing bit-wise parallel algorithm. Furthermore, the enhanced algorithm also reduces the amount of required memory for storing data for signal correlation.     

矢量数据的一种分层动态组织方法

提出矢量数据分层组织的一种动态结构,在该结构中,单点、单字符或符号作为基元,以属性串组织基元,并分层叠置。采用区别于链式结构的动态通用串结构及C语言予以实现。     

The CNSDTF topological vector model and structure

Geo-Spatial Data Transfer Standard is an important part of "National Spatial Data Infrastructure(NSDI)" ,as well as a necessary means for data sharing. "Chinese National Geo-Spatial Data Transfer Format (CNSDTF)" was approved by National Quality Technology Supervise Bureau in 1999 with the standard serial number of 17798-1999. It is designed to support vector and raster spatial data. This paper describes the vector part of CNSDTF, including design ideas, main characters, conceptual model, definition of spatial object, and file structure.     

A density-based approach for detecting network-constrained clusters in spatial point events

Existing spatial clustering methods primarily focus on points distributed in planar space. However, occurrence locations and background processes of most human mobility events within cities are constrained by the road network space. Here we describe a density-based clustering approach for objectively detecting clusters in network-constrained point events. First, the network-constrained Delaunay triangulation is constructed to facilitate the measurement of network distances between points. Then, a combination of network kernel density estimation and potential entropy is executed to determine the optimal neighbourhood size. Furthermore, all network-constrained events are tested under a null hypothesis to statistically identify core points with significantly high densities. Finally, spatial clusters can be formed by expanding from the identified core points. Experimental comparisons performed on the origin and destination points of taxis in Beijing demonstrate that the proposed method can ascertain network-constrained clusters precisely and significantly. The resulting time-dependent patterns of clusters will be informative for taxi route selections in the future.     

等距等高电磁波测距三角高程测量及精度分析

介绍了等距等高电磁波测距三角高程测量的原理，详细深入地分析了这种高程测量方法的精度，通过计算和作图表示，可直观地反映在不同条件下的精度变化情况，讨论了代替国家等级水准测量的范围和条件，可供生产实际和进一步研究参考。     

Quick Bird遥感影像的几何校正

以高分辨率的Quick Bird卫星数据为对象,经影像信息融合,使处理后的图像分辨率提高且接近真彩色,具有良好的判识效果;选择若干个GPS地面控制点作为参考点,以遥感图像处理软件ER Mapper6.2为平台,对图像进行二次多项式几何精校正,纠正后的图像点位误差在lm左右,说明纠正后的图像具有较高的几何精度.     

Exploring the spatial and temporal dynamics of land use in Xizhuang watershed of Yunnan, southwest China

Over the last two decades, China has introduced a series of agricultural and forestland use reforms, aiming to feed the largest population in the world and maintain ecological services locally and nationally. This paper studies the impacts of local government-driven reforestation on land use and land cover change, as well as its further impacts on livelihoods of upland farmers in Xizhuang watershed. An analysis of aerial photographs and ASTER satellite imagery from 1987 to 2002, respectively, showed that the forest has significantly increased at the expense of decreasing farmland. However, the monoculture reforestation of pine has caused both biophysical and socio-economic consequences. This case study also shows forestry decentralization in China remains incomplete. Land use and land cover change is also a political economic issue. Some of the reforms designed to protect forest resources have had a negative impact on rural livelihoods.     

Automatic placement of GIS vector map annotation in area feature by long-diagonal

IntroductionMap is a graphics expression of spatial infor-mation. Map language includes map symbolwhose basic languageis graphics ,and map anno-tation as nature language (letters) . Map annota-tion plays an i mportant role in computer aidedcartography and GIS.It is a complementarityformap graphics and makes the map hold richer in-formation[1].Map annotation is one of the international ar-duous problemsin automatic map generalization.With the development of computer technology ,the automatic …     

智能CAD中图的一种表示方法

试图提出广义结点概念，并给出图的一种表示方法。该方法用邻接表法表示广义结点与邻近广义结点的关系，用向量表示法表示单一属性广义结点链。在实现方法上，不采用链接表结构，而用动态通用串结构很好地实现了图的运算操作。并举例说明在智能地ＣＡＤ中的运用。     

MODELING FUZZY GEOGRAPHIC OBJECTS WITHIN FUZZY FIELDS

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