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1.
《测量评论》2013,45(77):302-306
AbstractAlthough during World War II field work on geodetic subjects other than those directly connected with the war effort remained practically in abeyance, the war provided unique opportunities for the study and execution of several interesting problems such as the linking of Indian triangulation with Iraq and Iran on the one hand and Siam and Malaya on the other. A detailed account of the Geodetic work of the Survey of India during the period 1939-47 is given in the Survey of India “Technical Report 1947—Part III, Geodetic Work”. 相似文献
2.
《测量评论》2013,45(14):472-484
Abstract Choice of Beacon.—The general question as to whether luminous or opaque signals should be used in ruling triangulation has recently been discussed in the Empire Survey Review (No.9, pp. 151–2 and No. 12, pp. 335–6). It may here be summarized that opaque beacons of suitable design are sufficiently accurate and offer the considerable advantages of being immediately available for subsequent work, of requiring little or no attention, and of being visible from all directions without rearrangement. Moreover, if of the tripod or quadripod type, they need not be dismounted during occupation of the station for observing, so that 0bservations by more than one observer are not interrupted. The only occasion for using luminous beacons arises from bad visibility, whether through atmospheric haze or lack of a suitable background or through the economic necessity of completing observations at night. These conditions are not peculiar to ruling triangulation. An ”all-round” type of luminous beacon—a pressure oil lamp or a rotating mirror system—can be used for nightwork or against a dark background, but single-direction luminous beacons are necessary to overcome haze. 相似文献
3.
《测量评论》2013,45(9):167-168
AbstractIn the reduction of geodetic triangulation the computation of the spherical excess of each triangle is of great importance; for unless the amount of spherical excess is known, the accuracy with which the angles have been observed cannot be assessed, nor can the triangle itself be computed by the simple formulae applicable to plane triangles. 相似文献
4.
《测量评论》2013,45(20):350-354
AbstractMost text-books on surveying limit their discussion of the correction of vertical angles for curvature of the earth and atmospheric refraction to the correction of angles taken with a theodolite during triangulation and omit any reference to those taken with a clinometer. This is rather illogical, as in well-observed triangulation, with all vertical angles measured in both directions, no correction for these effects is necessary, whilst in plane-tabling on small scales where sketching at considerable distances is frequently employed the application of corrections for these effects is essential. 相似文献
5.
《测量评论》2013,45(9):151-156
AbstractMr. Clendinning's article on “Signal Lamps” (E.S.R., vol. ii, pp. 15–18) raises a point of major importance in geodetic triangulation. I entirely agree with him that the sole use of heliographs—heliostats to the purist—is in most parts of the world out of date. I also think, and indeed am prepared to state categorically, that the use of acetylene lamps is out of date and was out of date many years ago. The Americans, who are always worth listening to on the economics of surveys, would not otherwise have replaced all their acetylene gear by electric beacons. The answer, in my experience, and for reasons which I shall endeavour to make clear, is generally, but not necessarily always, to provide both helio and electric lighting; but first I should like to summarize the conditions in which luminous signals should be used at all. 相似文献
6.
《测量评论》2013,45(92):242-254
AbstractThe application, in Oanada, of shoran electronic length measurement to surveying and mapping may be regarded as having been initiated in 1947, when experimental work by Federal Government bureaus was conducted in the vicinity of Ottawa over several long lines between stations of the first-order triangulation. During the succeeding two winters this work was continued, and the results indicated shoran as suitable for establishing position, in Canada's vast northland, quickly and with greater accuracy than by means of astronomic methods. It was realized that trilateration might fail in securing the necessary accuracy because of the many factors involved. Since no information was available, or even existed, from the experience of other survey organizations as to the error in position which might be generated in a comparatively long arc, the first work planned was for a 1100-mile axial-length arc between geodetic bases. This arc, situated in Manitoba and Saskatchewan, was measured in 1949 and 1950. The result indicated that shoran, with careful supervision of all details, could produce results of accuracy superior to astronomic positioning, which is the only reasonable and speedy alternative method of control for mapping at the present stage of development of the northern areas. 相似文献
7.
《测量评论》2013,45(16):72-80
AbstractIt was suggested some time ago in the Review (E.S.R., vol. ii, no. 9, p. 182) that observing procedure in a ruling triangulation should be made the subject of a discussion at the forthcoming Empire Survey Conference. I hope it will be. We shall perhaps learn why India finds thirty measures necessary, as no doubt they are necessary in India, whereas South Africa and Southern Rhodesia are able to secure much the same degree of accuracy from the same instrument with only eight; why Canada, again with the same instrument, prefers the golden mean of sixteen; why some of us still prefer the measurement of angles to directions vvhile others would insist entirely on the measurement of directions from a “close” R.O. It is only by pooling the experiences gained in diverse circumstances that we can avoid being overborne by our own successes or failures, encountered possibly in very exceptional circumstances which may not recur. 相似文献
8.
9.
《测量评论》2013,45(70):357-363
AbstractThere are no proper projections for use in geodetic work in a country which has great extensions both in latitude and longitude. For, if a single projection of any kind be applied in such a case, the linear and angular distortions would be so great at the boundary that it is very difficult or even impossible to apply the corrections to them. In order to render it possible for any projection to be applied, the area in question should be divided either into strips bounded by meridians or into zones bounded by parallels. In the former case the Transverse Mercator or Gauss’ projection may be used, while in the latter, the Lambert conformal projection is the most suitable. China is such a country as that mentioned above. It covers an area extending from 16°N. to 53°N. in latitude and of no less than sixty-five degrees in longitude. The problem of choosing a projection for geodetic work depends only on how the area is to be divided. It has been decided by the Central Land Survey of China to adopt the Lambert conformal projection as the basis for the co-ordinate system, and, in order to meet the requirements of geodetic work, the whole country is subdivided into eleven zones bounded by parallels including a spacing of 3½ degrees in latitude-difference. To each of these zones is applied a Lambert projection, properly chosen so as to fit it best. The two standard parallels of the projection are situated at one-seventh of the latitude-difference of the zone from the top and bottom. Thus, the spacing between the standard parallels is 2½ degrees. This gives a maximum value of the scale factor of less than one part in four thousand, thus reducing the distortions of any kind to a reasonable amount. The area between these parallels belongs to the zone proper, while those outside are the overlapping regions with the adjacent ones. All the zones can be extended indefinitely both eastwards and westwards to include the boundaries of the country. 相似文献
10.
《测量评论》2013,45(66):166-174
AbstractThe computation of geographical coordinates in a geodetic triangulation is usually carried out using Puissant's method, in which the assumption is made the sphere radius ν (the radius of curvature of the spheroid perpendicular to the meridian) not only touches the spheroid along the whole small circle of latitude ?,but also, since ρ (the radius of curvature in meridian) is very nearly equal to ν it makes such close contact with the spheroid that the lengths of sides and angles of a geodetic triangle may be considered identical on both sphere and spheroid. 相似文献
11.
《测量评论》2013,45(14):464-472
Abstract The Mythical Spheroid.—The preceding article dealt with the fact that the spheroid of reference is a myth and that, even if it were not, we could not get hold of it at any given place. In order to apply corrections to observed quantities or, more generally, to operate upon them mathematically, we must make some assumption such as that of the spheroidal level surface. Probably a lot of harm has been done by attaching the notion of too concrete a thing to the spheroid. Disputes and misconceptions have arisen. People talk of“putting the spheroid down at a point” and imagine that the obedient thing is still at their feet when they get to another point, perhaps distant, in their system of triangulation or what not. Actually the spheroid may be disobedient not only as regards the direction of the vertical but also because it is above their heads or below their feet. What happens is that at each point afresh the computer treats the observations as if they were made there on the surface of a spheroid. In the same way, but travelling still farther along the road of hypothesis, he may treat observations for astronomical positions as if the compensation for visible elevations were uniformly distributed as a deficiency of density down to a depth of 122·2 kilometres. That was the depth which happened to give the smallest sum of squares of residuals in a certain restricted area, but nobody imagines that it corresponds with a physical reality, especially the ·2! It was a convenient mathematical instrument which, once the theory was to be given a trial, had to be fashioned out of some assumption or another. All this has little to do with geodetic levelling but is meant to try to banish the spheroid out of the reader's mind or at least to the back of his mind. In what follows we shall be compelled to make a certain amount of use of the family of spheroids but always with the above strictures in view. 相似文献
12.
《测量评论》2013,45(32):85-89
AbstractThe necessity of transforming rectangular co-ordinates from one system of projection to another may arise from, various causes, One case, for example, with which the present writer is concerned involves the transformation, to the standard belt now in use, of the co-ordinates of some hundreds of points of a long existing triangulation projected a quarter of a, century ago on a, belt of Transverse Mercator projection, In this case conversion is complicated by the fact that the spheroid used in the original computation differs from that now adopted, and, also, the geodetic datums are not the same, The case in fact approaches the most general that can occur in practice, One step in one solution of this problem, however, is of perhaps wider Interest: that is, the transformation from one belt of Transverse Mercator projection to another when the spheroids and datums are identical. It is this special case which will be discussed here. 相似文献
13.
《测量评论》2013,45(65):131-134
Abstract1. In geodetic work a ‘Laplace Point’ connotes a place where both longitude and azimuth have been observed astronomically. Geodetic surveys emanate from an “origin” O, whose coordinates are derived from astronomical observations: and positions of any other points embraced by the survey can be calculated on the basis of an assumed figure of reference which in practice is a spheroid formed by the revolution of an ellipse about its minor axis. The coordinates (latitude = ?, longitude = λ and azimuth = A) so computed are designated “geodetic”. 相似文献
14.
《测量评论》2013,45(27):267-269
AbstractAfter the completion of Simms's Geodetic Chain in 1901 and the publication of the results in 1905—Volume iii of the Geodetic Survey of South Africa—nothing further of a geodetic nature was done until 1928 when a short chain was run westwards from Simms's chain, at about latitude 17° 10′, to fix the Copper Queen mining area. The Eastern Circuit was commenced shortly after this; it runs from Salisbury eastwards to the Portuguese Boundary, southwards through Umtali to about latitude 20° and then westwards, joining Simms's chain again to the east of Bulawayo. Another chain running north from Simms's work has been commenced near Bulawayo. The several series are exhibited on the outline map attached. 相似文献
15.
《测量评论》2013,45(2):66-71
AbstractThe Americans having started this hare suggested at the Stockholm Congress that a certain number of Laplace stations should be considered the hall-mark of any geodetic triangulation wherever situated. It is therefore pertinent, rather than impertinent, to examine the history of the North American datum at Meades Ranch, Kansas, to see whether the American situation is really known in America. 相似文献
16.
《测量评论》2013,45(30):457-462
AbstractIn the original geodetic series in Southern Rhodesia—completed by Mr Alexander Simms in 1901—the geographical coordinates of all stations were referred to the point SALISBURYas origin. The coordinates of SALISBURY were fixed by interchange of telegraphic signals with the Royal Observatory at the Cape for longitude, combined with astronomical determinations of time, latitude, and azimuth (see Vol. III, “Geodetic Survey of South Africa”). 相似文献
17.
《测量评论》2013,45(18):241-242
AbstractIn working out vertical heights on the Akuse-Kete Krachi chain of triangulation in the Gold Coast a fairly considerable difference was found between values of the coefficient of refraction obtained from observations taken during the day and those taken at night, the mean values being 0.069 for daylight observations to heliographs and 0.087 for night observations to lamps. This difference no doubt is due mainly to the condition of the atmosphere during the day differing from its condition during the night rather than to any effect due to different sources of light. A new chain has recently been observed in Western Ashanti, and the index of refraction for the daylight observations again gave a lower value than that obtained from the night observations, the figures being 0.073 and 0.099 respectively. For the night work three different sources of light were used, hurricane lamps for short lines, Tilley vapour-pressure lamps for lines of intermediate length, and McCaw acetylene signalling lamps by Watts for long lines. It occurred, therefore, to the writer to examine the results to see if the mean values of the index of refraction showed any variations for the different light sources, since it seemed reasonable to suppose that the constitution of the light emitted from each source would be different and hence that the coefficient of refraction might vary. 相似文献
18.
《测量评论》2013,45(60):221-227
AbstractIn a previous article in this Review, the writer endeavoured to show that chains of minor triangulation could be adjusted by plane rectangular co-ordinates ignoring the spherical form of the earth with little loss of accuracy, provided that the two ends were held fixed in position. It was demonstrated that the plane co-ordinates produced by the rigorous adjustment between the fixed starting and closing sides, differ by only a comparatively small amount from the projection co-ordinates produced by a rigorous adjustment on the Transverse Mercator projection. The saving in time when computing by plane co-ordinates as opposed to rigorous computation on the projection by any method will be apparent to any computer with experience of both methods. 相似文献
19.
《测量评论》2013,45(3):129-131
AbstractThe triangulation of Ceylon depends for its scale upon two bases, each about 5½ miles long, situated at Negombo on the West Coast (latitude 7° 10′) and at Batticaloa on the East Coast (latitude 7° 40′). Both bases are in low, flat country; brick towers up to 70 feet high had to be built over the terminals to enable observations to be taken to surrounding points. These lines have recently been re-measured. 相似文献
20.
《测量评论》2013,45(62):295-297
AbstractA Few notes will now be given on the subject of triangulation on which practically all the methods already outlined depend. If we have a triangulation ready for us on which to base our work, so much the better; but, if not, we must make every effort to carry one through either from our own measured base or from any existing points on the edge of our work. For reconnaissance survey, such a triangulation must be carried out with the greatest expedition; even if all refinements are sacrificed to speed, it is extraordinary how small the errors will be found to be when a more rigid triangulation is made. Any unorthodox method such as carrying through with a resected point or with an astronomical azimuth may be adopted. A bush will often make a good point to observe to, also piles of bushes with a flag on a reed or stick. 相似文献