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1.
王树连 《测绘工程》1997,6(3):40-45
概述魏晋南北朝时期的测绘管理及职官设置,疆域测量了及地图绘制,天文观测及其新发现等史实,勾画出了这一时期测绘发展的轮廓。  相似文献   

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喻沧 《测绘工程》1997,6(4):42-49
介绍隋、唐,五代时期测绘职官,天文大地测量,工程测量,地图制图等简史,盛唐时期是中国测绘继汉代以后发展的又一高峰。  相似文献   

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Rhind (1992) argued that government data policies and Intellectual Property Righr (IPR) considerations would play an increasingly large role in influencing the use of GIS. This has proved to be correct in general but the non-technical factors affecting data collection, supply, and price have become ever more complex. Indeed, one characteristic of the present situation is that it is now impossible to consider the legal, economic, and public policy issues in isolation. Consequently, this paper sets out to identify the interactions between them and the areas of conflict. It draws upon the literature of a much wider area than traditional GIS. This approach is essential because of two factors. The first is that GIS databases are presently of modest commercial value compared to some other data and hence key decisions on IPR, etc are being made outside our discipline. The second is that the nature of GIS databases is mutating rapidly through the wider use of multi-media and of the internet. It is concluded that the future is largely unpredictable in any detail since the interactions differ in different countries and at different moments in time. In many cases, however, revenue generation from sales or leasing of data or from services built upon data exploitation is likely to be a characteristic of both the public and the private sectors. Such charging has observable beneficial effects to set against the frequently claimed disadvantages, whether measured in financial, legal, or public access terms.  相似文献   

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An analysis of the drainage network of a part of Sivasagar district, Assam, India, is undertaken to reveal the role of neotectonic activity of the area. A number of fluvial geomorphic anomalies have been identified in the area. A prominent annular drainage anomaly is displayed by the major rivers—the Dikhu, Jhanzi, Namdang, Dorika and Disang, whose courses are carved in response to the ongoing tectonic deformation in the area. This study reveals that the development of topography and drainage system of the study area have been influenced by active subsurface geological structures. Formation of paleochannels, compressed meanders, reticulate streams, swamps, sagging of grounds, stream alignments, lineaments, knick points and abandonment of rivers as well as development of smaller drainage anomalies also substantiate the active nature of the subsurface structures.  相似文献   

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Coastal resources viz., coral reefs, seagrasses, mangroves, and coastal land features viz., sandy beach, mudflats and salt pan/aquaculture ponds were classified and assessed in the Palk Bay region of the south-east coast of India using IRS LISS III satellite image (1996, 2000, 2002 and 2004). The study recorded an areal coverage of 286.95 ha of reef area during 2004, which is 177.54 ha lesser than that of the reef area of 1996. The reef vegetation composed mainly of seaweeds has gained over 29.44 ha during the same period. Likewise, sand over reef area has also increased alarmingly i.e. 120.34 ha between 1996 and 2004. The seagrass beds of Munaikkadu region of the Palk Bay are comparatively protected and have gained over 7.5 ha between 1996 and 2004. It has been found that both the dense (2.99 ha) and sparse (36.45 ha) mangroves have gained their areal coverage considerably between 1996 and 2004. Whereas in Devipattinam region, many anthropogenic pressures are exerted only on the seagrass resources which has led to the reduction of over 785.5 ha of dense seagrass beds between 1996 and 2004. The study clearly indicated that the resources are under the pressures of low to high threats, especially the coral reefs and seagrasses, if the pressures continue, coastal resources of the Palk Bay may face serious threats of destruction in this part of the Bay in the years to come.  相似文献   

9.
吴承园 《测绘工程》1998,7(2):75-79
概述辽、金、元三代有关测绘的管理和机构、职官设置,各在测绘状况成果,着重介绍了元代的测绘技术、发明创造及著述。  相似文献   

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The study of the photolinears and the groundwater flow directions in the Lonavala area of the Pune distrtict suggests the relationship between these two parameters. In the western part of the Lonavala area the groundwater flow lines are running along a dark toned linear trending N 20° - 30°W. This linear is a fracture controlled linear valley covered by dense vegetation which is supported by the groundwater channelised along this linear. The higher specific capacities of the dugwells situated along the trend of this linear also suggest the movement of groundwater along the linear.  相似文献   

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Geoid, topography, and the Bouguer plate or shell   总被引:1,自引:1,他引:1  
 Topography plays an important role in solving many geodetic and geophysical problems. In the evaluation of a topographical effect, a planar model, a spherical model or an even more sophisticated model can be used. In most applications, the planar model is considered appropriate: recall the evaluation of gravity reductions of the free-air, Poincaré–Prey or Bouguer kind. For some applications, such as the evaluation of topographical effects in gravimetric geoid computations, it is preferable or even necessary to use at least the spherical model of topography. In modelling the topographical effect, the bulk of the effect comes from the Bouguer plate, in the case of the planar model, or from the Bouguer shell, in the case of the spherical model. The difference between the effects of the Bouguer plate and the Bouguer shell is studied, while the effect of the rest of topography, the terrain, is discussed elsewhere. It is argued that the classical Bouguer plate gravity reduction should be considered as a mathematical construction with unclear physical meaning. It is shown that if the reduction is understood to be reducing observed gravity onto the geoid through the Bouguer plate/shell then both models give practically identical answers, as associated with Poincaré's and Prey's work. It is shown why only the spherical model should be used in the evaluation of topographical effects in the Stokes–Helmert solution of Stokes' boundary-value problem. The reason for this is that the Bouguer plate model does not allow for a physically acceptable condensation scheme for the topography. Received: 24 December 1999 / Accepted: 11 December 2000  相似文献   

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In the present study, we investigate the effects of urbanization growth on river morphology in the downstream part of Talar River, east of Mazandaran Province, Iran. Morphological and morphometric parameters in 10 equal sub-reaches were defined along a 11.5 km reach of the Talar River after land cover maps were produced for 1955, 1968, 1994, 2005 and 2013. Land cover types changed extremely during the study period. Residential lands were found to have increased in area by about 1631%, while forest land and riparian vegetation decreased in by approximately 99.9 and 96.2%, respectively. The results of morphometric and morphological factors showed that average channel width (W) for all 11.5 km of the study river decreased by 84% during the study period, while the flow length increased by about 2.14%.  相似文献   

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Satellite gravity missions, such as CHAMP, GRACE and GOCE, and airborne gravity campaigns in areas without ground gravity will enhance the present knowledge of the Earths gravity field. Combining the new gravity information with the existing marine and ground gravity anomalies is a major task for which the mathematical tools have to be developed. In one way or another they will be based on the spectral information available for gravity data and noise. The integration of the additional gravity information from satellite and airborne campaigns with existing data has not been studied in sufficient detail and a number of open questions remain. A strategy for the combination of satellite, airborne and ground measurements is presented. It is based on ideas independently introduced by Sjöberg and Wenzel in the early 1980s and has been modified by using a quasi-deterministic approach for the determination of the weighting functions. In addition, the original approach of Sjöberg and Wenzel is extended to more than two measurement types, combining the Meissl scheme with the least-squares spectral combination. Satellite (or geopotential) harmonics, ground gravity anomalies and airborne gravity disturbances are used as measurement types, but other combinations are possible. Different error characteristics and measurement-type combinations and their impact on the final solution are studied. Using simulated data, the results show a geoid accuracy in the centimeter range for a local test area.  相似文献   

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Balat River has abandoned its westerly course and followed an old course to the east during the recent past. This has lead to the recognition of an oscillation pattern for this river with its periodic shift where the course if confined to the zone bounded by the two channel courses.  相似文献   

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Peri-glacial studies of the Samudra Tapu glacier reveal three stages of well preserved moraines which are also marked by fluvial overprinting. The signatures of fluvial outwashes over the otherwise morainal deposits have been utilized in estimating the extent of palaeo-lake in the valley of Samudra Tapu glacier of the Chandra basin. Distance and thickness of snout of the glacier and its morainal deposits is estimated by the Laser Range Finder. With the change in the position of the snout there is a change in the extent and orientation of the lake. Recent expedition to the glacier confirms this process to be continuing. The study is important in reconstructing formation of the lake with respect to snout position of the glacier. Based on ground truth, fast melting of the snout is confirmed from year 2004 onwards, with the development of fresh end/terminal moraine. The study reveals that the snout region of the Samudra Tapu glacier is thinning and retreating at an alarming rate and is enlarging the lake extent. The development of fresh terminal moraine has the potential to impound the fast melting glacial waters which in turn can pose serious threat to the downstream regions of the Chandra valley.  相似文献   

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Based on the method of virial equations, the integro-differential equations governing the physical figure of the earth are derived. Volume forces of gravitational type and surface forces of stress type are assumed. Initial stress is represented by the H. TAKEUCHI (1951) model. Equilibrium figures for different earth models-elastic, elastic under initial stress, liquid-are studied. It is proved that non-liquid earth models allow ellipsoidal structures of MACLAURIN type.  相似文献   

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