NOTE ON THE EVANS RESECTION METHOD

Abstract

IN certain classes of work such as extended reconnaissance in new country frequent fixing of position by resection is a useful and economical method to use. The three-point resection, with safeguards against gross error, occurs frequently. Its main disadvantage is the repetition of a laborious computation.     

THE YEAR 1934 IN SARAWAK

Abstract

General.— The year 1934 has seen on the survey side an active continuation of trig. and cadastral surveys and on the land side standardization of procedure and routine. Good progress has been made in both branches. The surplus of revenue over expenditure, noted last year for almost the first time, has been very considerably increased, being of the order of eighty-two thousand dollars.     

THE YEAR 1931 IN NIGERIA

Abstract

The outstanding feature of 1931 was undoubtedly the rapid fall in the revenue of the Colony and Protectorate, which half-way through the year necessitated drastic reductions in Government expenditure, and in the case of the Survey Department led to the termination of the appointments of 15 European surveyors, I lithographer, and 20 members of the African staff. This cut, equivalent to a reduction of 28 per cent. of European and of 13 per cent. of African personnel, had unfortunately to be carried out at the height of the topographical and trigonometrical season and naturally entailed the closing down of some survey operations and the re-posting of officers to other duties to readjust the reduced personnel to more urgent requirements.     

Ability to detect and locate gross errors on DEM matching algorithm

Abstract

Digital elevation model (DEM) matching techniques have been extended to DEM deformation detection by substituting a robust estimator for the least squares estimator, in which terrain changes are treated as gross errors. However, all existing methods only emphasise their deformation detecting ability, and neglect another important aspect: only when the gross error can be detected and located, can this system be useful. This paper employs the gross error judgement matrix as a tool to make an in-depth analysis of this problem. The theoretical analyses and experimental results show that observations in the DEM matching algorithm in real applications have the ability to detect and locate gross errors. Therefore, treating the terrain changes as gross errors is theoretically feasible, allowing real DEM deformations to be detected by employing a surface matching technique.     

SARAWAK LANDS AND SURVEY DEPARTMENT, 1940

Abstract

Financial.-The revenue collection for the year was 440,790.30, consisting of Land revenue 336,422.97 and Mining revenue 104,360.33. The expenditure for the year was 206,476.02, of which only 192.05 was Special. This does not include salaries, amounting to 14,313, of Officers seconded for Food Control. Expenditure was again below normal because of the secondment of staff to other duties.     

THE SURVEYOR'S LEVEL YESTERDAY AND TO-DAY

Abstract

The last twenty-five years have been remarkable for the progress made in the application of science to instrument design and manufacture. Certain instruments such as the Surveyor's Level appeared twenty-five years ago to have almost reached finality of design; but during the intervening period the improvements made have been of so radical a nature that the progress made has been greater than during any corresponding period. In short, the modern level is a more efficient instrument than its prototype and in spite of reductions in size and weight is, capable of yielding more accurate results with a less expenditure of time and energy. In order to appreciate fully how radical these changes have been, a direct comparison may be made between a first-class level as made twenty-five years ago and a similar instrument as made to-day. Twenty-five years ago it was not possible to obtain a level that could be relied upon to remain in adjustment; one that could be quickly checked and easily corrected offered distinct advantages. The Reversible Level was designed with this end in view; and it is proposed to select such an instrument having an objective aperture of 1·65 inches and to compare it with a modern instrument of the same aperture. The focal length of the telescope of the Reversible Level was 16 inches, and the weight of the instrument with its box was 21½ lbs. (Plate VIII, fig. 1). Many surveyors with long experience of this type still speak highly of its reliability and accuracy; it certainly compared very favourably with other instruments of its period.     

A statistical filter for geodetic observations

A method for filtering of geodetic observationwhich leaves the final result normally distributed, is presented. Furthermore, it is shown that if you sacrifice100.a% of all the observations you may be (1−β).100% sure that a gross error of the size Δ is rejected. Another and, may be intuitively, more appealing method is presented; the two methods are compared and it is shown why Method 1 should be preferred to Method 2 for geodetic purposes. Finally the two methods are demonstrated in some numerical examples.     

SIR DAVID GILL AND THE GEODETIC SURVEY OF SOUTH AFRICA AND THE ARC OF THE 30TH MERIDIAN

Abstract

In the memoir of the late Capt. G. T. McCaw which appeared in the January number of this Review (vii, 47,2), reference was made to the part which the late Sir David Gill played in the origin of the work on the survey of the Arc of the 30th Meridian in Africa. This year is the centenary of Gill's birth, as he was born in June 1843, and it is therefore timely to give some account of his work during his long term of office as Her Majesty's Astronomer at the Cape which resulted inthe inception and completion of the Geodetic Survey of South Africa and the survey of the Arc to the southern shores of Lake Tanganyika. He died on 24th January 1914.     

THE ISLANDS OF THE TRISTAN D'ACUNHA GROUP

Abstract

In January, 1934, a report was received from the Royal Research Ship Discovery II that the positions of Inaccessible and Nightingale Islands in the Tristan d'Acunha group were incorrectly shown on British Admiralty chart No. 1769. The report originated from local information, and was to some extent confirmed by patent log distances run by Discovery II, and by sea sights, but no really definite evidence as to the correct position of the two islands was received. In effect, the report merely stated that both Inaccessible and Nightingale Islands were considerably nearer to Tristan Island than as charted.     

DEVIATION OF THE VERTICAL. DISCUSSION

Abstract

The following is a report of the discussion on the paper by Mr. A. R. Robbins on “Deviation of the Vertical” which was read at a meeting of the Land Surveying Division of the Royal Institution of Chartered Surveyors held on Tuesday, 12th December, 1950, and which was published in the January issue of this Review (xi, 79, 28–36).     

THE PRIMARY TRIANGULATION OF SARAWAK

Abstract

Historical.—When my predecessor, Mr N. A. Middlemas, was seconded from the Survey Department of Malaya in 1925, the survey framework of the State was technically negligible.     

THE CALCULATION OF THE HEIGHT OF KILIMANJARO

Abstract

The observations to height Kilimanjaro were made from two ground stations, Domberg (5,081·6 ft.) and Lelatema (5,323.1 ft.) and from a point called Kibo near Kaiser Wilhelm Spitze which is regarded as the highest point on the crater rim. It was originally intended to include a third ground station, Kifaru, but it was discovered that the ice cap obstructed observations between this point and the top.     

THE CONFORMAL TRANSFORMATION OF A NETWORK OF TRIANGULATION

Abstract

In a recent issue of this Review, an example is given of the conformal transformation of a network of triangulation using Newton's interpolation formula with divided differences. While the application of the method appears to be new, attention should be drawn to the fact that Kruger employed Lagrange's interpolation formula in a discussion and extension of the Schols method in a paper which was published in the Zeitschrift für Vermessungswesen in 1896. A reference to this paper was given at the end of the paper, “Adjustment of the Secondary Triangulation of South Africa”, published in a previous issue of the E.S.R. (iv, 30, 480).     

CONDITION FOR THE CONSTRUCTION OF A CONFORMAL PROJECTION

Abstract

In the Empire Survey Review for October 1938 (iv, 30, 480) a simple demonstration of the condition to be satisfied for conformal representation was given. This condition may be expressed by the equation w = f(z), where w and z are complex variables representing corresponding points in the w-plane and z-plane respectively, and f(z) is an analytic function of z.     

CORRECTIONS TO THE TENSION IN A SURVEYING TAPE FOR THE EFFECT OF THE TOTAL LOAD BETWEEN THE MEASURING HEAD AND THE STRAINING WEIGHT

Abstract

Consider the case of a surveying tape (or portion of a tape) suspended in a single horizontal catenary, the tension at either or both ends being applied by means of a weight W attached to a cord which passes over a pulley to the end of the tape.     

THE USE OF THE MAGNETIC NEEDLE ON SURVEYS IN TRINIDAD

Abstract

In Trinidad the magnetic needle is used on all secondary surveys. The term “compass surveys” was given, unfortunately, to these secondary surveys in order to distinguish them from surveys carried out in open country in the ordinary manner with the theodolite oriented by means of solar observations or by bearings obtained direct from the trigonometrical framework.     

THE NEW GEODETIC TAVISTOCK THEODOLITE

Abstract

Work on the original Geodetic Tavistock Theodolite was commenced in the autumn of 1931, and after suitable tests this instrument was sent out to East Africa and used on the East African Arc. Bt Major M. Hotine, R.E., writing in the E.S.R. of April 1935 (no. 16, vol. iii), stated: “The Tavistock instrument, although a first model, gave uniformly satisfactory service throughout and was used for over half the main angular observations.”     

THE CONVERSION OF CO-ORDINATES FROM THE CASSINI TO THE TRANSVERSE MERCATOR PROJECTION

Abstract

1. The Secondary and Tertiary Triangulations of the six counties of Northern Ireland which were observed about 1900 were computed county by county each on its own meridian on a Cassini projection using Airy's figure of the earth. Although a number of points common to two or more counties were fixed no attempt was made to bring the separate counties into sympathy either with each other or even with the old Primary triangulation as adjusted by Clarke in 1856.     

THE TRANSVERSE MERCATOR PROJECTION OF THE SPHEROID

Abstract

In January 1940, in a paper entitled “The Transverse Mercator Projection: A Critical Examination” (E.S.R., v, 35, 285), the late Captain G. T. McCaw obtained expressions for the co-ordinates of a point on the Transverse Mercator projection of the spheroid which appeared to cast suspicion on the results originally derived by Gauss. McCaw considered, in fact, that his expressions gave the true measures of the co-ordinates, and that the Gauss method contained some invalidity. He requested readers to report any flaw that might be discovered in his work, but apparently no such flaw had been detected at the time of his death. It can be shown, however, that the invalidities are in McCaw's methods, and there seems no reason for doubting the results derived by the Gauss method.