Quasi indicatrix approach for distortion visualization and analysis for map projections     

Ibrahim Oztug Bildirici 《International journal of geographical information science》2013,27(12):2295-2309

Tissot’s indicatrix or ellipse of distortion is a diagram that is the projection of an infinitesimal circle on the original surface. It is normally an ellipse of which elongation depends on the amount of distortion caused by map projection. It provides a medium for analyzing existing projections and developing new ones. The ellipse can be scaled and depicted on the map for visualization purposes. This paper presents an alternative approach, in which the projection of a finite small circle on the sphere is used. Its projection is normally an ellipse that can be very close to Tissot’s indicatrix, and is called quasi indicatrix, here. Its parameters can be derived from the forward projection equations without using partial derivatives. Therefore, it is a useful and practical approach from a programmer’s point of view. The quasi indicatrix approach is also numerically tested on Aitoff–Hammer projection with a set of points. The indicatrix parameters obtained by using this approach deviate 0.5% from the ground truths at most, being the average less than 0.2%.  相似文献   

Climatic Change and Desert Vegetation Distribution: Assessing Thirty Years of Change in Southern Nevada's Mojave Desert     

Ross J. Guida  Scott R. Abella  William J. Smith Jr.  Haroon Stephen  Chris L. Roberts 《The Professional geographer》2013,65(2):311-322

A major theme in physical geography and biogeography is understanding how vegetation changes across geographic gradients during climate change. We assess shifts in distributions of fifteen Mojave Desert plant species based on a 2008 resurvey of 103 vegetation transects that were established in 1979. We model changes in species distributions using Maximum Entropy (Maxent) with environmental and climate variables to predict probability of species’ occurrences. Climate during the ten-year period preceding the 2008 vegetation survey was 1.5°C warmer and 3 cm per year of precipitation drier than the ten years preceding 1979. Species inhabiting the highest elevations and strongly correlated with precipitation displayed areal reductions from 1979 through 2008.  相似文献   

Choosing a Suitable Projection for Navigation in the Arctic     

Andriani Skopeliti  Lysandros Tsoulos 《Marine Geodesy》2013,36(2):234-259

Navigation at sea is based on Electronic Chart Display and Information Systems (ECDIS) that allow for the use of a limited number of projections. As navigation in the Arctic region becomes a reality due to the progressive melting of the polar ice cap, a re-examination of the most suitable projections for navigation in the Arctic becomes timely. Several projections are proposed in the literature for this area. In our approach, the selection is based on an analytical study utilizing three criteria: the control of the magnitude of distortions within acceptable limits, the shape of great circles (GCs) and rhumb lines/loxodromes, and the shape of the graticule lines portrayed on the chart. The analysis carried out shows that to fulfill the set criteria, the arctic area should be divided into Arctic and sub-Arctic regions. More specifically, for the Arctic region the Azimuthal Polar Equidistant projection and the Azimuthal Polar Stereographic projection are the most suitable ones. For the sub-Arctic region, the Lambert Conformal Conic and the Conic Equidistant projection are considered more appropriate. All four projections proposed can be used for both the traditional nautical chart and the ECDIS, and both are considered as the starting point for further study of specific ECDIS requirements.  相似文献   

Techniques for slope stability analysis: Site specific studies from Idukki district,Kerala     

S. Sreekumar 《Journal of the Geological Society of India》2009,73(6):813-820

The occurrences of slope failures are frequent in Idukki district of Kerala state particularly along the road cuttings and hill slopes causing disruption in traffic, loss of lives and property. This demands a critical evaluation of stability of slopes along the hill roads. This paper deals with stability analysis of a typical hard rock profile at Chuzhappu and a lateritic profile at Kumili along the road connecting Kottayam and Kumili. A large number of factors have been examined and studied; the orientation of discontinuities has been identified as one of the major inherent factors influencing slope instability along Chuzhappu hard rock profile. These have been analysed carefully using stereographic/equal area projection technique in order to determine the vulnerability to slope failure and to understand the type of rock slide that can occur in this profile. The buoyant force of water acting along the discontinuities after heavy rain storm further aids the down slope movement. As the laterite slope is mostly homogeneous, Bishops method and Swedish method were adopted for stability analysis of laterite slope at Kumili. The study also examines the efficacy and applicability of the different methods employed in soil mechanics to assess the stability of laterite slope.The results obtained by this method are compared by actual field conditions. The stability assessment indicates that two sectors at Chuzhappu and one sector at Kumili profile are at the geo-technical threshold of failure, when piezometric head rises during rainstorm. The study indicates that these methods are highly useful in determining the Factor of Safety in profiles with similar geological setting.  相似文献   

Banach空间中非扩张映像的强收敛性     

李全刚 《成都信息工程学院学报》2010,(6):321-323

在实光滑和一致凸Banach空间中通过引入广义度量投影,证明了一个关于非扩张映像的修正Mann迭代序列的强收敛性定理。目的是利用广义度量投影来修改Nakajo与Takahashi的迭代方案,并将Nakajo与Taka—hashi文中所对应的主要结果由Hilbert空间推广到实光滑和一致凸Banach空间。  相似文献   

Development implications of demographic trends and projections for an arid region:: the case of the Badia Research and Development Project area of Jordan     

Allan M. Findlay  Mohammed Maani 《Applied geography (Sevenoaks, England)》1999,19(4):29

Development planners in arid areas face many difficulties in preparing appropriate strategies. Their task is made harder by the dearth of reliable demographic information. This paper presents population projections for the arid area of eastern Jordan covered by the Badia Research and Development Project and evaluates the economic and social implications of these projections over the next 20 years. The paper argues that conventional demographic forecasting methods are extremely problematic when applied to a population such as this. Furthermore, the pastoral economy, which has in the past been the main source of livelihood, cannot hope to sustain the region's future population. High fertility rates will continue to place great stress on the educational and health infrastructure. If appropriate planning responses are not achieved, the demographic regime of the Badia project area and the quality of life of the population may continue to diverge from the patterns found in other parts of Jordan.  相似文献   

21世纪西北太平洋台风变化预估   总被引：3，自引：1，他引：2  

赵宗慈  罗勇  高学杰  徐影 《气候变化研究进展》2007,3(3):158-161

对近年多个气候模式考虑不同的人类排放情景作了总结,并对21世纪西北太平洋台风变化作了预估。研究表明,集成多个气候模式考虑人类排放情景,预估到21世纪后期,西北太平洋年总编号台风数可能减少,但强台风数及其降水和风速可能增强。需要强调的是,台风的长期预估是极其困难的,存在极大的不确定性,有待作更深入的研究。  相似文献   

不同情景达到碳中和下中国区域气候变化的预估          下载免费PDF全文

邓荔  朱欢欢  江志红 《大气科学学报》2022,45(3):364-375

利用第6次耦合模式比较计划（CMIP6）中的9个全球气候模式的模拟结果,通过CO₂浓度达峰时间确定SSP1-1.9和SSP1-2.6两种情景下的全球碳中和时间,预估了全球碳中和下中国区域气候较历史参考期（1995—2014年）的未来变化,分析不同时间达到碳中和下气候响应差异,并与未实现碳中和的SSP2-4.5情景下的气候变化对比。结果表明,SSP1-1.9和SSP1-2.6情景下全球达到碳中和的时间分别为2041年和2063年,相较于历史参考期,SSP1-1.9/SSP1-2.6下中国区域平均年气温上升1.22/1.58℃,平均年降水量增加7.1％/9.9％。SSP1-2.6（晚碳中和）较SSP1-1.9（早碳中和）情景下年均温增高约0.36℃,最大升温区位于西南及高原地区。对降水而言,晚碳中和较早碳中和全国平均年降水量增加约2.7％。全年及夏季降水量显著增加区主要在西北,新疆地区出现降水增加超过8％的大值区,冬季则集中于黄河中下游,增幅也超过8％。未碳中和的SSP2-4.5情景下中国区域的升温显著强于SSP1-2.6（碳中和）情景,年平均气温高约0.61℃,西北地区是升温差别大值区,其中新疆部分地区增加升温超过0.8℃。SSP2-4.5较SSP1-2.6情景年降水量在西北地区增加显著,内蒙古西北部最大增加超过10％。有无碳中和对冬季降水影响更大,SSP2-4.5情景下新疆部分地区降水增加比SSP1-2.6下多20％左右,云南部分地区则少15％左右,表明有无碳中和对气候的影响远大于早晚碳中和。  相似文献   

The Anomalous Mei-yu Rainfall of Summer 2020 from a Circulation Clustering Perspective: Current and Possible Future Prevalence※     

Robin T.CLARK  Peili WU  Lixia ZHANG  Chaofan LI 《大气科学进展》2021,38(12):2010-2022

Highly unusual amounts of rainfall were seen in the 2020 summer in many parts of China, Japan, and South Korea. At the intercontinental scale, case studies have attributed this exceptional event to a displacement of the climatological western North Pacific subtropical anticyclone, potentially associated Indian Ocean sea surface temperature patterns and a mid-latitude wave train emanating from the North Atlantic. Using clusters of spatial patterns of sea level pressure, we show that an unprecedented 80％ of the 2020 summer days in East Asia were dominated by clusters of surface pressure greater than normal over the South China Sea. By examining the rainfall and water vapor fluxes in other years when these clusters were also prevalent, we find that the frequency of these types of clusters was likely to have been largely responsible for the unusual rainfall of 2020. From two ensembles of future climate projections, we show that summers like 2020 in East Asia may become more frequent and considerably wetter in a warmer world with an enhanced moisture supply.  相似文献   

加权残值法与等角投影数值变换     

李家权  张勤 《地球科学与环境学报》1989,(3)

本文介绍了描述等角投影变换的Dirichlet模型和用加权残值法求解该模型的一般原理和方法,并给出了应用上述方法所获得的某些等角投影变换的数值公式。文章最后指出,由于应用数值方法,有可能形成一门新的学科,即计算地图投影学。  相似文献