REPRODUCTION OF THE 1/1,250 AND 1/2,500 SCALE NATIONAL PLANS,OF GREAT BRITAIN

Abstract

Field work for the 1/1,250 scale re-survey of Great Britain was fully described in an article by Brigadier R. P.Wheeler in the April, 1948, issue of this Review (ix, 68, 234–247). The object of this article is to outline the method’ of reproduction of these plans and of the resultant 1/2,500 scale plans of urban areas. The 1/2,500 series covering rural areas is a separate problem, one of revision rather than re-survey. Experiments are in hand now to find out the best ways to provide field material and produce the final plans on National Grid sheet lines. The 1/1,250 scale series will contain about forty thousand plans and the 1/2,500 series of the same areas about nine thousand. It is therefore important that production methods should be straightforward and maintain an economical balance between the use of men and machines.     

THE EFFECTS OF ECCENTRICITY AND MISPLACED INDICES OF DIVIDED CIRCLES

Abstract

Special precautions are taken in the workshop to ensure that divided circles are so mounted that the point from which the circle graduations radiate lies accurately on the axis about which rotation of the circle and reading index or indices takes place. If, through some accident, eccentricity is present, it is still possible to obtain accurate readings if the instrument is used to the best advantage, and the object of the following notes is to assist the surveyor to this end. It will be found that errors arising from eccentricity can be made to cancel out, except in the case of a vertical circle fitted with a single reading index.     

THE DERIVATION OF CERTAIN PROJECTION FORMULAE FOR THE SPHERE

Abstract

The purpose of this article is to make available to readers of the Review a simple method of derivation from first principles of the projection farmulae for same of the more impartant normal conical projections.     

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.     

INSTRUCTIONS FOR THE USE OF THE PRISMATIC ASTROLABE AND PROGRAMME FINDER

Abstract

The problem of finding the latitude and longitude of various points on the surface of the earth is one which has been studied for hundreds of years.     

THE STEREOGRAPHIC SOLUTION OF THE SPHERICAL TRIANGLE

Abstract

At the suggestion of Mr. T. H. Corfield, who has himself given two solutions (E.S.R., No. 12, pp. 345–6) of Mr. A. J. Potter's problem, I venture to submit a third solution, which has at least the merit of simplicity.     

THE ADJUSTMENT OF A FIRST-ORDER LEVELLING NETWORK

Abstract

In the E.S.R. January and April numbers of 1955, Vol. xiii, Nos. 95 and 96, Mr. Hsuan-Loh Su described the “Adjustment of a Level Net by Successive Approximations and by Electrical Analogy”. It does not seem to be as generally known as it should be that the rigid least square solution can be greatly simplified by utilizing the electrical analogy and solving by Kirchhoff's method. The method as detailed below has been in use for over 40 years.     

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).     

NOTE ON THE REDUCTION OF CIRCUMMERIDIAN ALTITUDES TO THE MERIDIAN

Abstract

The method of reducing circummeridian altitudes or zenith distances to the meridian, using the factors m and n as tabulated by Chauvenet, is well known. The following method, which does not use these factars, has been faund both more convenient and more accurate in practice. The formula can be easily obtained by expanding m and n in powers of t, but far the sake af campleteness the derivatian is here given from the beginning.     

THE APPLICATION OF THE GAUSS METHOD OF COLLIMATION TO THE ADJUSTMENT OF SURVEY INSTRUMENTS

Abstract

Gauss's method of collimation is usually given scant attention in survey text-books. The following notes are based on experiments carried out at Accra in making a collimation base, the collimator being a Watts 2I-inch self-adjusting level fitted with a parallelplate micrometer.     

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.     

TRIGONOMETRICAL HEIGHTS AND THE COEFFICIENT OF TERRESTRIAL REFRACTION

Abstract

Mr. A. J. Morley has contributed a series of articles in the Review (E.S.R., iv, 23, 16; iv, 25, 136 and vi, 40, 76) on the adjustment of trigonometrical levels and the evaluation of the coefficient of terrestrial refraction with a view to ascertaining how other Colonies and Dominions deal with these problems. This object is very commendable as several problems concerning both the observational and theoretical sides arise in height determinations, regarding which there is not much guidance in the usual treatises on the subject.     

A SEMI-GRAPHIC CONSTRUCTION FOR THE CONICAL ORTHOMORPHIC PROJECTION WITH ONE STANDARD PARALLELt

Abstract

The advantages of orthomorphic projections for topographical maps, whether for civil or military uses, have been increasingly realised in recent years. This has led to their gradual adoption as bases for map series by the leading countries, the conical type having been adopted in France for the new 1 : 50,000 maps, in Canada for the National Defence maps and in Britain by the Directorate of Military Survey for some useful European series. Appreciation of the nature and properties of graticules can best be achieved through an understanding of the theory of the projection system, whether the exposition be mathematically or partly graphically developed. Whereas the cylindrical and zenithal types of the orthomorphic projections have some explanation in graphical form there has been no comparable alternative to the difficult mathematical treatment of the conical type. The semi-graphic method presented here has been developed to contribute towards such a graphical exposition and in its method demands only a modest mathematical ability.     

EVALUATING THE DISTORTION INVOLVED IN THE READJUSTMENT OF A NETWORK: THE SCHOLS ADJUSTMENT AS A POSSIBLE CRITERION

Abstract

The object of the present paper is to provide a criterion for assessing the value of a network of surveyed points in the light of a subsequent accurate coordination of control points in the area.     

A METHOD FOR THE DETERMINATION OF THE DISTORTIONS OF THE IMAGE FORMED BY A MULTIPLEX PROJECTOR

Abstract

A Method is described for the determination of the resultant of the radial and tangential components of the distortion of the image produced by a Multiplex projector.     

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.     

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.     

TACHEOMETRIC SURVEYING AND THE USE OF THE DIFFERENTIAL SLIDE RULE

Abstract

In the E.S.R. No. 17 of July 1935, page 138, there appeared an article by Prof. F. A. Redmond on “The use of Even Angles in Stadia Surveying”. Since I have given this method a six-months' test in the field, using Prof. Redmond's “Tacheometric Tables” for the reduction of the measurements, the conclusions reached may be of some interest.