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1.
《测量评论》2013,45(91):231-232
AbstractThe correction to observed vertical angles for curvature and refraction can be found by adding a log factor to the log distance, which gives the log of the correction in seconds. This factor is 8·144 for metres and 7·628 for feet. The examples will make this clear. For machine computation, the correction in seconds can be obtained by multiplying the length in metres by 0.0139 or the length in feet by 0·00425. Alternatively, this can be done on the slide. rule by dividing the distance in metres by 72 or in feet by 235. The mean coefficient of refraction is taken as 0·07. 相似文献
2.
《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
3.
《测量评论》2013,45(79):19-24
AbstractA problem frequently encountered by surveyors in carrying out a system of triangulation, is the adjustment of a network of lower order triangulation to make it geometrically consistent with an existing triangulation of a higher order. For example, in Fig. 1 it will be assumed that the positions of the stations A, B, and C have already been determined and that it is now required to determine the positions of the stations a, b, c, d, e and f from the measured values of the internal angles of the network of triangulation shown. In practice, several different solutions have been suggested, ranging from rigorous least squares methods to semi-graphical solutions. The method described in this article is believed to be original and may prove of interest to surveyors. 相似文献
4.
《测量评论》2013,45(12):357-367
AbstractThe only essential difference between geodetic triangulation and any other of the fifteen “orders” of triangulation—which were once proposed, and happily rejected, at an International Conference—is that steps are taken to secure the high degree of accuracy necessary over the large areas to be covered. Some of the steps taken to secure increased accuracy may well be used to insure economy in secondary work, as for instance the use of fewer readings of a large instrument, or the use of luminous signals in conditions of poor visibility; while any surveyor may at any time have to connect his work to a geodetic triangulation, using much the same methods. 相似文献
5.
《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
6.
7.
《测量评论》2013,45(78):353-366
AbstractIT has been assumed in the past that because angles for triangulation are usually observed by the direction method, therefore it must be more correct theoretically to perform the least-square adjustments by directions rather than by angles. It is fairly obvious that an adjustment of the same figure by directions will not give the same result as an adjustment by angles: the unknowns in each case are different and the number of directions is usually about 25 per cent. greater than the number of angles for the same figure. Strictly, the least square method is only applicable to observations from which all systematic errors have been eliminated, and in which the remaining errors are truly accidental. It is generally safe to assume that most survey errOlS consist of a random and a systematic part. Rarely, if ever, is it possible to state that all systematic error has been eliminated, strive how we may to take all precautions against it. 相似文献
8.
《测量评论》2013,45(80):65-69
AbstractOne method of reducing a series of pointings taken upon a close circumpolar star is to average the recorded horizontal angles and to obtain the average of the separate star azimuths by applying a curvature correction to the azimuth calculated from the average of the hour angles of the various pointings. 相似文献
9.
《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
10.
《测量评论》2013,45(54):311-314
AbstractThere has always been a marked difference of opinion on the relative merits of the methods of bearings and of angles as applied to triangulation, though it is probable that the majority of writers prefer the method of bearings for first-order work. The subject was mentioned in a recent issue of this Review (vii, 47, 19). 相似文献
11.
《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
12.
《测量评论》2013,45(23):44-48
AbstractIt sometimes happens that the limits or an area to be mapped by plane-table methods extend somewhat outside the scope of the previously observed triangulation. If the area outside the existing triangulation is not too great, it is often most convenient for the plane-tabler to extend the control himself as far as he requires it. 相似文献
13.
《测量评论》2013,45(9)
AbstractThe following method will be found better and quicker than the usual logarithmic process in computing the co-ordinates of intersected points in minor triangulation and traverse work. Let A and B be two stations whose co-ordinates (x 1 y 1), (x 2 y 2) are known. Let P be an intersected point whose co-ordinates (x, y) we wish to determine. Let α and β be the observed angles at A and B respectively. 相似文献
14.
《测量评论》2013,45(7):24-28
AbstractMeasured deviations of the vertical have been used in support, or in destruction, of such pleasant little diversions as the theory of isostasy. They have also been used to adjust a triang~lation for swing, by methods which may fairly be criticized; but they have not, as far as I know, been used for reducing the horizontal measures of a triangulation to the standard conventional level of the spheroid of reference. In most cases such corrections would, of course, be too small to worry about, but it by no means follows that they are always small. In the case of a continental arc of meridian traversing a very disturbed mountainous region exhibiting certain constant tendencies, it should at least be demonstrated that they are small before the question can be considered finally settled. 相似文献
15.
《测量评论》2013,45(96):70-75
AbstractThe following paper describes some of the results obtained on it, tour of the Katsina and Kano Provinces of Northern Nigeria between November 1953 and February 1954. The purpose of the tour was to obtain latitudes and longitudes by astronomical observations for air photo mapping control in the northern parts of these provinces where triangulation is not available. The area is mostly flat and sandy. 相似文献
16.
《测量评论》2013,45(21):386-395
AbstractAt the Conference of Empire Survey Officers held in London in 1931, an historical sketch was given of the progress of triangulation in Nigeria from its commencement to the end of the 1930 season, together with a brief summary of the proposed future programme. Since that date substantial progress has been made, and the recent completion of several important chains of triangulation and of the main precise traverse framework through the thickly forested regions of the Southern Provinces seems a convenient opportunity to place on record the present position. 相似文献
17.
《International Journal of Digital Earth》2013,6(5):504-520
Abstract Because the removal of topographic effects is one the most important pre-processing steps when extracting information from satellite images in digital Earth applications, the problem of differential terrain illumination on satellite imagery has been investigated for at least 20 years. As there is no superior topographic correction method applicable to all areas and all images, a comparison of topographic normalization methods in different regions and images is necessary. In this study, common topographic correction methods were applied on an ALOS AVNIR-2 image of a rugged forest area, and the results were evaluated through different criteria. The results show that the simple correction methods [Cosine, Sun-Canopy-sensor (SCS), and Minnaert correction] are inefficient in exceptionally rough forests. Among the improved correction methods (SCS+C, modified Minnaert, and pixel-based Minnaert), the best result was achieved using a pixel-based Minnaert approach in which a separate correction factor in various slope angles is used. Thus, this method should be considered for topographic correction, especially in forests with severe topography. 相似文献
18.
《测量评论》2013,45(25):136-140
AbstractIn a previous article on this subject (Empire Survey Review, January 1937) the writer sought to show that for trigonometrical observations of vertical angles made near noon in the Tropics the coefficient of refraction depends chiefly on height above ground level in the case of stations sited within a few hundred feet above the general level of the ground surface. Indeed, the computed values of the coefficient K show a definite and appreciable increase with “h”, the height of the observing station above ground level; it is usually assumed that K decreases with increase in height above the Mean-Sea-Level surface. From analysis of the results obtained by varying h but holding the heights above Mean Sea Level fixed the writer came to the conclusion that the variations in K could only be due to abnormal values of dt/dh and d2t/dh2, “t” denoting the air temperature. Now it is generally recognized by meteorologists that abnormal lapse-rates of temperature do frequently occur in the lower air layers in the Tropics; but up to the present time no temperature soundings in Nigeria are available. Recently, however, the writer came across the results of the aerological soundings made by an expedition in East Africa during the year 1908. The results of many of the soundings were of no use for the purpose of this paper; many of the observations were not taken at or near noon, and in others counterlapses of temperature in the lower layers indicated that conditions were not normal. A set of observations taken at Mombasa between 10 and 11 a.m. were eventually chosen as offering an example of what might reasonably occur in the lower layers of the atmosphere. 相似文献
19.
With the increasing number of precise navigation and positioning applications using Global Navigation Satellite Systems (GNSS)
such as the Global Positioning System (GPS), higher order ionospheric effects and their correction become more and more important.
Whereas the first-order error can be completely eliminated by a linear combination of dual- frequency measurements, the second-
and third-order residual effects remain uncorrected in this approach. To quantify the second-order residual effect, a simple
formula has been derived for GNSS users in Germany. Our proposed correction algorithm reduces the second-order effects to
a residual error of fractions of 1 mm up to 2 mm at a vertical total electron content level of 1018 electrons/m2 (100 TECU), depending on satellite azimuth and elevation angles. The correction formula can be implemented in real-time applications
as it does not require the knowledge of the geomagnetic field or the electron density distribution in the ionosphere along
the signal path. It is expected that the correction will enable more accurate positioning using the line-of-sight carrier-phase
measurements. 相似文献
20.