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1.
《测量评论》2013,45(75):218-227
AbstractThe oblique or general case of the gnomonic projection receives little serious attention in most text books on map projections and in the works which do include the theory it is unfortunately developed with unnecessary complexity. In consequence it is much less widely understood than are the special cases represented by the polar and equatorial forms. Yet the oblique form provides a gratieule which has proved incomparably more useful than either of the two Inore obvious and popular special cases. Thus, oblique cases have provided the graticules for the series of gnomonic charts of the oceans published by the Hydrographic Department of the Admiralty; the G.S.G.S. Consol Plotting Charts and the Gnomonic Fixing Chart (prepared specially for use with long range radio aids to navigation) are all oblique gnomonic graticules as are the special purpose charts for position fixing from radio bearings published by the Admiralty. In addition, all large scale port plans included in the range of Admiralty charts are drawn on a modified gnomonic. It is only in connection with the production of facets for “near globes” that one can point to the use of the polar and equatorial cases of the gnomonic and even here the greater number of facets are produced as oblique cases. 相似文献
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为解决传统球面高斯投影公式在极点处的奇异问题,通过引入余纬度对原有投影公式进行改进,推导了极区高斯投影非奇异公式;基于该公式推导了极区经纬线投影方程,并结合日晷投影进行长度变形及子午线偏移角分析。结果表明,在余纬度很小时,高斯投影与日晷投影非常接近,即其经纬网与日晷投影近似;在极圈内高斯投影长度变形小于日晷投影,其经线与日晷投影经线的最大偏移角为2.4688°,而在纬度80°以上,最大偏移角为0.4386°。极区非奇异高斯投影公式满足了极区内连续投影的需求,可为极区海图绘制提供理论依据。 相似文献
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《测量评论》2013,45(87):2-12
AbstractThe Hydrographic Department of the Admiralty performs a number of functions appropriate to its status as an Admiralty Department but it is also responsible through its head, the Hydrographer of the Navy, for the compilation, publication and distribution to the Merchant Navy and the public, as well as to the Fleet, of Admiralty charts and of other nautical publications concerned with the safety of navigation. The latter comprise the “Admiralty Sailing Directions”, the “Admiralty Tide and Tidal Stream Tables”, the the “Admiralty List of Lights” and the “Admiralty List of Radio Signals ”. 相似文献
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《测量评论》2013,45(14):502-505
AbstractFor several years it had been realized that aneroids in the Gold Coast showed a distinct lag in the readings when subject to fairly large changes of height. The range of height in the Colony, however, being relatively small and control heights fairly numerous, little interest was taken in the cause, which was generally thought to be due to hysteresis. * All aneroids in use on the Gold Coast are graduated on Airy's scale which is based on latitude 45° and temperature 50° F. In 1921 Mr. C. L. T. Griffith, at that time Chief Instructor of the Survey School, carried out various tests with a number of aneroids, and from these tests concluded that the main source of error arose from inappropriate graduation of the height-scale relative to pressure; using as constants latitude 15°, temperature 86° F., and mean humidity 67 per cent., he worked out a proposed general scale for the Tropics. Ten years later the purchase for test purposes of new aneroids graduated to this scale was considered but was eventually postponed when it was learnt that the question of a special scale for use in the Tropics was under consideration at home by a special Committee consisting of representatives of the Admiralty, War Office, Air Ministry, and National Physical Laboratory. 相似文献
7.
《International Journal of Digital Earth》2013,6(2):109-121
Abstract Bad weather in many countries limits the use of optical satellite imageries in spatial and temporal monitoring of the environment. In this paper, a series of low-altitude oblique aerial photos taken on daily, weekly and monthly intervals were used to monitor the geomorphological changes in the upper part of the Mersey Estuary, northwestern England. This low-altitude aerial photo methodology reveals itself to be a satisfying compromise between cost, accuracy and difficulty of implementation. It offered a large amount of information on a spatial and temporal scale aiding in the understanding of channel mobility. This was an important consideration in the sitting and installation of new bridge pier foundations. This series of oblique aerial photos was used in a dynamic model to determine the migration of the ebb channel and was effective in identifying the main route of flow. Few uncertainties were encountered and the level of accuracy achieved in resolving these uncertainties in the images was in the range from 40 cm to a maximum of 1.7 m. This was compared with historical navigation charts and showed good correlation. Further applications are required to improve the quality of the data output from these images and the development of the technique. 相似文献
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《测量评论》2013,45(92):263-276
AbstractMost books on the technique of map compilation omit a detailed consideration of projections on the grounds that this subject is adequately treated at length elsewhere. Texts on map projections, however, are largely theoretical and rarely consider the practical problem of the proper choice and use of the graticules which are otherwise so ably described. An investigation of this little explored field has produced the following picture which it is thought may be of wider interest. A study of the fundamental properties which influence the choice of map projections is followed by a survey of projections in use, considered in relation to the fundamental properties. 相似文献
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研究了极球面投影海图上准确便捷地量测距离的方法。推导了极球面投影下大圆航线和等角航线的方程,形状分析表明极区宜采用大圆航线量测距离;根据极球面投影下直线的几何意义推导了其距离计算公式,距离差值分析表明可用直线代替大圆航线准确量测距离;根据极球面投影上小圆线投影为圆的性质,提出了一种基于等距圆的准确便捷的距离量测方法,以满足极球面投影海图的极区导航应用需要。 相似文献
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《测量评论》2013,45(94):372-376
AbstractIn the October 1953 issue of this Review (E.S.R. xii, 90, 174), Mr. J. G. Freislich has written of the difficulties of a southern hemisphere computer attempting to use astronomical formulae from a textbook prepared for use in the northern hemisphere. He proposes a solution in which different conventions are adopted in the two hemispheres, leading to different formulae for the two cases, a solution which the present writer does not favour. 相似文献
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S. H. Laurila 《Journal of Geodesy》1969,43(2):139-153
The main environmental problem in tracking a satellite through the atmosphere is in finding the most probable value of the
mean refractive index. In this paper, the mean refractive index is computed as a four-part model. The troposphere is treated
as one altitude range from sea level to 9 kilometers, and the stratosphere is divided into three altitude ranges, 9 to 18,
18 to 27, and 27 to 36 kilometers. At 36 kilometers, the N-value is approximately equal to two and reduces rapidly to zero.
By the use of theEssen formula in radio wave application and the modifiedKohlrausch formula in light wave application, point-to-point values of the refractive index are computed through these altitude ranges.
The polynomial expansion of second order from the basic exponential function is selected as the model, and the curve-fitting
adjustments of the computed values are established separately to each altitude range to obtain coefficients A, B, and C.
A model based on the U. S. Standard Atmosphere, 1962, is used as the reference to which four sets of actual soundings made
in Lihue, Hawaii and Fairbanks, Alaska on February 3 and July 2, 1966, are compared. The results show that the parabolic adjustment
has a very high reliability. In the use of standard atmosphere, the standard error of the refractive index through the total
altitude range of 0 to 36 kilometers, and at the 70° zenith distance, equal only ±7 millimeters when radio waves are utilized,
and ±3 millimeters when light waves are utilized.
Paper presented at Conference on Refraction Effects in Geodesy and Electronic Distance Measurement, University of New South
Wales, 5–8 November 1968. Hawaii Institute of Geophysics Contribution No. 239. 相似文献
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《测量评论》2013,45(66):138-147
AbstractThat special air maps might be necessary was realised as long ago as 1909 when the use of maps in connection with balloons was being discussed: but there was little progress and Bleriot's flight in the same year imposed a completely new outlook. At first, with the air speeds common in the early days, it was possible for the aviator to use standard topographical maps on scales such as half or one inch to one mile and navigate by the identification of prominent landmarks. It was soon realised however that certain features were more outstanding than others and this observation was incorporated in one of the very first attempts to produce an "aero" map made in 1912. In this the roads, railways and lakes were emphasised by hand colouring on a photoprint of the one inch Ordnance Survey sheet. The practice of using, or hand amending, existing topographical maps continued in the early days of the 1914-18 war but the growth of the R.F.C. and the R.N.A.S. emphasised the need for specific air maps. By the end of the war the R.N.A.S. had special air charts for use over the coastal areas of the British Isles, and a special aviation map of France had been produced for the R.F.C. These maps were probably the first ever made in quantity for use in the air but they did not differ radically from the existing topographical series except in the simplification of certain detail and the showing of additional data of value to the airman -aerodrolnes, landing grounds, dangers etc. Air speeds were still not very high and flying was largely confined to fine weather so that the main form of navigation continued to be by the direct reading of maps. 相似文献
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《测量评论》2013,45(93):321-334
AbstractAn attempt has been made to answer this question by consideration of special cases in which the real errors are known. Some very interesting general results have been obtained, including a good estimate for the coefficient of correlation between real errors and L.S. corrections. The difference between L.S. solutions by angles and by directions has been further clarified. 相似文献
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《The Cartographic journal》2013,50(1):48-60
AbstractThe Lack hitherto of studies of cycle-touring mapping in Britain is noted, and some basic attributes of cycle touring, including speed, daily distance, gradients and wind, are described. Essential and desirable qualities for a cycle-touring map are enumerated, including the need to depict all rural routes available to cyclists; it is concluded that the optimum scale is in the range 1:100 000–1:126 720, and that relief should by contours at an interval not greater than 30 metres. National mapping in the optimum scale range which were published after 1945 are then reviewed, and reasons suggested as to why none has been kept in print. The mapping available for cycle touring in Britain in 2001 is Ordnance Survey (OS) 1:50 000 Landranger series contains all the necessary information, it is too bulky to be suitable; and that most of the other maps published in the optimum scale range have inadequate relief information and all offer very limited geographical cover. The potential competition for the OS 1:50 000 from a national map series in the optimum scale range is acknowledged, and an outline specification for a 1:125 000 series is described, which seeks to minimize that competiton whilst providing all the necessary information for cycle touring. 相似文献
17.
Five separate polar motion series are examined in order to understand what portion of their variations at periods exceeding
several years represents true polar motion. The data since the development of space-geodetic techniques (by themselves insufficient
for study of long-period motion), and a variety of historical astrometric data sets, allow the following tentative conclusions:
retrograde long-period polar motion below about −0.2 cpy (cycles per year) in pre-space-geodetic data (pre-1976) is dominantly
noise. For 1976–1992, there is poor agreement between space-geodetic and astrometric series over the range −0.2 to +0.2 cpy,
demonstrating that classical astrometry lacked the precision to monitor polar motion in this frequency range. It is concluded
that all the pre-1976 astrometric polar motion data are likely to be dominated by noise at periods exceeding about 10 years.
The exception to this is possibly a linear trend found in some astrometric and space geodetic series. At frequencies above
prograde +0.2 cpy (periods shorter than about 5 years), historical astrometric data may be of sufficient quality for comparisons
with geophysical excitation time series. Even in the era of space geodesy, significant differences are found in long-period
variations in published polar motion time series.
Received: 27 March 2001 / Accepted: 15 October 2001 相似文献
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none 《The Cartographic journal》2013,50(2):191-201
AbstractVegetation and rural land use show some of the greatest variety both in what and in how they are depicted on topographic maps. This paper discusses the various approaches that have been adopted to the selection of information to be shown on non-specialist maps. It also looks at the different ways in which vegetation and rural land use are depicted on a range of published map. 相似文献
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