首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 562 毫秒
1.
Analyses and Solutions of Errors on GPS／GLONASS Positioning   总被引：1，自引：0，他引：1  
This paper focuses mainly on the major errors and their reduction approaches pertaining to combined GPS/GLONASS positioning.To determine thd difference in the time reference systems,different receiver clock offsets are introduced with respect to GPS and GLONASS system time.A more desirable method for introducing a independent unknown parameter of fifth receiver,which can be canceled out when forming difference measurements,is discussed.The error of orbit integration and the error of transformation parameters are addressed in detail.Results of numerical integration are give.To deal with the influence of ionospheric delay,a method for forming dual-frequency ionospheric free carrier phase measurements is detailed.  相似文献   

2.
Introduction Thepotentialvulnerabilityofsatellitenaviga tionsystemthatreliesongroundstationsisthat thesystemwouldbreakdownifgroundstations weredestroyed,whichcannotmeettherequire mentofnavigationwarfare[1].Withthedevelop mentofsuchspace basedsystemsasgrou…  相似文献   

3.
Through analyzing the principle of data sharing in the database system, this paper discusses the principle and method for integrating and sharing GIS data by data engine, introduces a way to achieve the high integration and sharing of GIS data on the basis of VCT in VC , and provides the method for uniting VCT into RDBMS in order to implement a spatial database with object-oriented data model.  相似文献   

4.
Pixel-based or texture-based classification technique individually does not yield an appropriate result in classifying the high spatial resolution remote sensing imagery since it comprises textured and non-textured regions. In this study, Hölder exponents (HE) and variance (VAR) are used together to transform the image for measuring texture. A threshold is derived to segment the transformed image into textured and non-textured regions. Subsequently, the original image is extracted into textured and non-textured regions using this segmented image mask. Afterward, extracted textured region is classified using ISODATA classification algorithm considering HE, VAR, and intensity values of individual pixel of textured region. And extracted non-textured region of the image is classified using ISODATA classification algorithm. In case of non-textured region, HE and VAR value of individual pixel is not considered for classification for significant textural variation is not found among different classes. Consequently, the classified outputs of non-textured and textured regions that are generated independently are merged together to get the final classified image. IKONOS 1 m PAN images are classified using the proposed algorithm, and the classification accuracy is more than 88%.  相似文献   

5.
The present study aims to estimate the loss of land use/cover and infrastructure facilities due the submergence by constructing the reservoir over the River Godavari at Polavaram Village. Detailed Land use/cover mapping has been carried out using LISS-III sensor data of IRS P6 satellite and linked to socio-economic data to analyze the administrative boundary wise environmental impact assessment in the study area. Land use/cover features are estimated from the Remote Sensing data through visual interpretation. Area covered below the 45.72 m contour above the mean sea level (MSL) is taken as submerged area due to the dam construction. Total area under submergence is estimated to be 58,658 ha, where 159 villages of three districts are affected by the project. The total population to be rehabilitated is about 1.2 lakhs, out of which maximum affected are Scheduled Tribes (58,781). Besides this, about 311 educational institutions, 202 medical institutions, 37 credit institutions and 55 postal institutions will be submerged due to the project. Further, nine mining sites, 24 tourist/historical sites and 78 agro-based industries will be displaced. The total road length of 673 km will go under submergence.  相似文献   

6.
  相似文献   

7.
Glyphs are small geometric shapes that in geovisualization are often used to represent multidimensional spatial data. The aim of this study is to investigate the effectiveness of their two types – star and polyline glyphs, as they can encode the same message and can provide similar functionality. Thus, if the two glyph types are similar and can be used for the same data, the question arises as to which of them better facilitates various user tasks. To address this question, an empirical study of 26 individual users is conducted to investigate differences in user performance for polyline and star glyphs shown either in a grid plot or on a map display. In this study, a task-based approach with eye-tracking is applied, as well as a subjective questionnaire and a psychological test of cognitive style. The finding is that polyline glyphs better facilitate tasks when datapoint values in glyphs are to be read, whereas star glyphs are better when a visual search among glyphs is to be done. Moreover, the results reveal that the map display works better than the grid plot. If star glyphs are to be used, the key (legend) needs to be better incorporated into a visual interface.  相似文献   

8.
Net primary production (NPP) is a crucial feature of ecosystem function and structure. Furthermore, precipitation use efficiency (PUE) is a critical indicator for exploring NPP in grassland ecosystem responses to variations in precipitation and temperature. In this study, we examined the spatial patterns of NPP and PUE in China’s grasslands from 2000 to 2010 and explored the effects of environmental factors on NPP and PUE at different scales. The results showed first that the spatial distribution of NPP and PUE decreased from the northeast to southwest. NPP increased in most places across China’s grasslands; however, there was no obvious change in PUE during 2000–2010. Second, in most regions across China’s grasslands, positive and negative correlations existed between precipitation and NPP and PUE, respectively. The spatial distribution of the relationship between temperature and NPP and PUE was consistent with the relationship between precipitation with NPP and PUE. Finally, for the gradients of the various environmental factors in different regional grassland ecosystems, on the Tibetan Plateau, there were unimodal correlations between precipitation with NPP and PUE and aridity with NPP and PUE, but a positive linear correlation existed for temperature with NPP and PUE. However, in the Inner Mongolian Plateau, there were positive correlations between precipitation and NPP, temperature and NPP, and aridity and both NPP and PUE and negative correlations between precipitations and PUE and temperature and PUE. Our findings improve understanding of grassland ecosystem responses to global climate change and provide a basis for the protection of grassland ecosystems in arid and semi-arid regions.  相似文献   

9.
A scheme for an automatic road surface modeling from a noisy point cloud is presented. The normal vectors of the point cloud are estimated by distance-weighted fitting of local plane. Then, an automati...  相似文献   

10.
Abstract

Fighting the 1914–18 war largely on enemy territory in both the east and the west, German was at a disadvantage compared to the Allies when it came to survey and mapping as it did have access to much of the geodetic, topographic and cartographic data, relating to this terrain, necessary for modern warfare — in particular for artillery survey. German and Austria did, however, have a commanding lead in terrestrial and aerial photogrammetry, and the latter was to prove crucial in the production of accurate large-scale maps of enemy and occupied territory. Despite strong forces of conservatism in the high and field commands and in the artillery and military survey organizations, new air survey methods based on the photogoniometer and radial triangulation were rapidly developed. Through continual laboratory and field experimentation and testing, German was to increase her lead in aerial photogrammetry, and by the end of the war had not only set up a completely new air survey organization but was developing a new generation of optical-mechanical stereoplotting instruments of great precision. German progress was not, however, evident in all fields of military survey, and this paper examines the approaches taken by German to survey and mapping on the Western Front, and briefly compares and contrasts them with those of the Allies.  相似文献   

11.
Much progress has been made in the field of web-based cartography through standards developed by the Open Geospatial Consortium (OGC). While automated access and presentation of cartographic data have been defined, the services for automated generalization are yet to be standardized. This paper aims to show advantages of applying the service concept to generalization and suggests several classification schemas of generalization services at different levels of granularity. A detailed explanation of a real implemented Generalization Service is provided. We show how software developers can make their generalization functionality available as a service and how these services can be accessed dynamically. For the implementation, the open source Java Unified Mapping Platform (JUMP) was extended to work as a framework for generalization. Generalization services could be used in different application scenarios, for instance as a middleware component extending a web map service with adaptive zooming or as stand-alone services supporting the production of topographic maps by national mapping agencies. They may also allow the development of a common research platform, where researchers would have access to a common generalization framework.  相似文献   

12.
Monitoring of river width and centerline is one of the most important activities in river engineering. Changes in the width and center line can be attributed to several reasons and monitoring these changes can be conveniently achieved with the aid of remote sensing images. In this study, digital image processing techniques have been implemented using the image processing tool-box available in MATLAB for studying temporal variations of width and centerline of the river Brahmaputra in its 300 Km reach in the state of Assam, India. The current study uses relatively high resolution imageries acquired from the LANDSAT series of satellites. Apart from the LANDSAT imageries, the low resolution imageries acquired by MODIS program is also used in order to see the variation in the obtained results. The evaluation of the results shows that the digital image processing technique is very handy and can be applied to obtain the centerline and width of a river. The evaluation also shows that the low resolution image can also be used for obtaining centerline of a river. However, it may give erroneous result when width of the river is narrow or very large.  相似文献   

13.
Urban system is shaped by the interactions between different regions and regions planned by the government, then reshaped by human activities and residents’ needs. Understanding the changes of regional structure and dynamics of city function based on the residents’ movement demand are important to evaluate and adjust the planning and management of urban services and internal structures. This paper constructed a probabilistic factor model on the basis of probabilistic latent semantic analysis and tensor decomposition, for purpose of understanding the higher order interactive population mobility and its impact on urban structure changes. First, a four-dimensional tensor of time (T)?×?week (W)?×?origin (O)?×?destination (D) was constructed to identify the day-to-day activities in three time modes and weekly regularity of weekday/weekend pattern. Then we reclassified the urban regions based on the space clustering formed by the space factor matrix and core tensor. Finally, we further analysed the space–time interaction on different time scales to deduce the actual function and connection strength of each region. Our research shows that the application of individual-based spatial–temporal data in human mobility and space–time interaction study can help to analyse urban spatial structure and understand the actual regional function from a new perspective.  相似文献   

14.
The veracity of land evaluation is tightly related to the reasonable weights of land evaluation fac- tors. By mapping qualitative linguistic words into a fine-changeable cloud drops and translating the uncertain factor conditions into quantitative values with the uncertain illation based on cloud model, and then, inte- grating correlation analysis, a new way of figuring out the weight of land evaluation factors is proposed. It may solve the limitations of the conventional ways.  相似文献   

15.
Multi-technique space geodetic analysis software has been developed which allows to combine data on the observation level. In addition to local tie information, site-wise common parameters, i.e., troposphere and clocks, can be estimated with this software. Thus, it will be discussed how common parameters have to be estimated and where biases/offsets need to be taken into account. To test such a novel concept, Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) data from the CONT11 campaign are being utilized. Since the VLBI baselines of this campaign extend over several thousands of kilometers, GPS data are processed in precise-point positioning mode and satellite orbits and clocks are kept fixed to the IGS final products. From the obtained results, it can be shown that the combination of space geodetic data on the observation level leads to a consistent improvement of station position repeatability as well as nuisance parameters like troposphere estimates. Furthermore, estimation of common parameters (troposphere or clocks) at co-located sites helps to improve the solution further and derive an utmost physically consistent model of the concerned parameters.  相似文献   

16.
There have been rapid population and accelerating urban growth with associated changes in land use and soil degradation in northeast China, an important grain-producing region. The development of integrated use of remote sensing, geographic information systems, and combined cellular automata– Markov models has provided new means of assessing changes in land use and land cover, and has enabled projection of trajectories into the future. We applied such techniques to the prefecture-level city of Harbin, the tenth largest city in China. We found that there had been significant losses of the land uses termed “cropland”, “grassland”, “wetland”, and “floodplain” in favour of “built-up land” and lesser transformations from “floodplain” to “forestland” and “water body” over the 18-year period. However, the transition was not a simple process but a complex network of changes, interchanges, and multiple transitions. In the absence of effective land use policies, projection of past trajectories into a balance state in the future would result in the decline of cropland from 65.6% to 46.9% and the increase of built-up area from 7.7% to 23.0% relative to the total area of the prefecture in 1989. It also led to the virtual elimination of land use types such as unused wetland and floodplain.  相似文献   

17.
Incremental LOD can be transmitted on the network as a stream, then users on the clients can easily catch the skeleton of terrain without downloading all the data from the server. Detailed information in a local part can be added gradually when users zoom it in without redundant data transmission in this procedure .To do this, an incremental LOD method is put forward according to the regular arrangement of grid. This method applies arbitrary sized grid terrains and is not restricted to square ones with a side measuring 2^k 1 samples. Maximum height errors are recorded when the LOD is preprocessed and it can be visualized with the geometrical Mipmaps to reduce the screen error.  相似文献   

18.
IntroductionThe GRACE (gravity recovery and cli mate ex-peri ment) mission,twin satellites flying in for-mation ,which carries several key payloadsinclu-ding KBR (K-band ranging) system, waslaunchedin 2002 . The unique design of GRACEmissionis expected to lead to ani mprovement inseveral orders of magnitude in these gravitymeasurements and allow much i mproved resolu-tion of the Earth gravity field of finer scale overbothland and ocean to study a lot of geosciencesphenomena[1]. Though th…  相似文献   

19.
Combining the dense GPS and gravity observation data in Sichuan-Yunnan area, where there are the relatively complete active tectonic zones and seismic data, this paper applies the geodesy and geophysical inversion technique and the advanced numerical simulation to the synthesis study of geodesy inversion to find the dynamic process of tectonic movement and deformation in the area and finally to investigate the kinematics characteristic of the geological structure of different layer and different scale. This paper discusses the kinematics, dynamics model about the crustal movement of active blocks in Sichuan-Yunnan area and its adjacent areas.  相似文献   

20.
Satellite-to-Satellite Tracking in low-low model （SST-Ⅱ） is a new technique to resolve the series of problems met in the determination of the earth＇s gravity field. As the key technique of SST-Ⅱ, KBR can get SST-Ⅱ measurements directly. So the KBR performance analysis is the first step in SST-Ⅱ design. In this paper, assuming that the satellite pairs of SST-Ⅱ are in near circle polar orbits, the spectrum relationship between the earth gravity field and KBR is established using analytic method. And then some examples are analyzed, the suggestions and conclusions are drawn from these examples. The research results could be taken as a reference for future satellite gravity project of China.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号