GEODETIC SIGNALS IN SOUTHERN RHODESIA

Abstract

So much has been written in the Empire Survey Review and other publications on the somewhat controversial subject of “Luminous or Opaque Signals in Geodetic and Primary Triangulation” that it may be of interest to give an outline of the types of signals used on such work in Southern Rhodesia, with particular reference to the completion of the Eastern Geodetic Circuit in 1935 and the type of signal that it has been decided to adopt for future work.     

INTERPOLATING FROM TRAVERSE TABLES TO SECONDS

Abstract

In the Empire Survey Review, no. 4, 1932, Mr. Clendinning has described a method of interpolating from traverse tables to seconds. Below is another method, due to Prof. Nekrassov, for use with traverse tables published by him. The method is described in The Geodezist, Moscow, 1936, no. I, pp. 47–52.     

NOTES ON THE GEODETIC SURVEY OF SOUTHERN RHODESIA

Abstract

Triangulation.—Apart from Simms' Geodetic Chain, Gordon's Chain, the Copper Queen Limb, and a section of the Victoria and Umtali Series, all the primary triangulation shown on the accompanying map has been executed since 1933. The work of Simms and Gordon has been remodelled, however, being greatly strengthened, and these chains are now called Simms' and Gordon's Series. For an explanation and plan of the above Series, see “A Note on the Trigonometrical Survey of S. Rhodesia”, in the Empire Survey Review, no. 27, vol. iv.     

IMPROVING THE PERFORMANCE OF WILD PRECISION THEODOLITES

Abstract

IN the July issue of the Empire Survey Review, vol. ii, no. 13, pp· 424–8, there appeared a review of precise theodolite investigations carried out by the present writers; the original papers were published in the March, 1934, number of the Canadian Journal of Research of the National Research Council, Ottawa. The elaboration of some points which could not be given much space either in the original papers or in the review may be of interest.     

LATERAL DISPLACEMENT OF SIGNALS OBSERVED

Abstract

I notice that in the last two numbers of the Empire Survey Review a lateral displacement is mentioned or implied.     

SOME EFFECTS OF PULLEY ECCENTRICITY IN BASE MEASURING APPARATUS

Abstract

The comprehensive paper on the suspension of tapes by M. Hotine in the January, 1939, issue of the Empire Survey Review (v, 31, 2) did not contain any reference to this question, as was pointed out by A. J. Morley in a letter published on page 261 in the same volume (v, 34, 261). A brief analysis has been made by F. Yates of the theoretical effects of pulley eccentricity and misalignment (“Gold Coast Survey Department Records” VoL III, 1931, page 43) but I have not seen any further reference to the subject and have recently experienced the effects of such a defect in our own apparatus, so the followingnotes nlay be of interest. Before proceeding to details I will describe briefly those parts of the apparatus which are considered here and give a short summary of the whole paper.     

THE EAST AFRICAN ARC

Abstract

It 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.     

THE UGANDA MAlLO SYSTEM

Abstract

The survey of “mailos” or native estates in the Kingdom of Buganda has taken a prominent place in the annual programme of the Survey Department of Uganda for over 30 years past. The survey, which has covered some 17,000 square miles and is now practically complete, has some unusual features, and although it has no claims to refinement or to great precision, a short account of its history and workings may be of general interest. The system of land settlement introduced by Sir Harry Johnston has already been described in the Empire Survey Review (“The Surveyor and the Politician”, by H. B. Thomas, vol. ii, p. 28).     

SOME SUGGESTIONS FOR SPEEDING UP WORK ON TOPOGRAPHICAL SURVEYS

Abstract

This paper includes a certain amount of material appearing in articles by the writer published at various times in the Empire Survey Review, but it seems convenient to embody these articles as part of one connected paper.     

TRIALS OF A SURVEYOR-MODERN VERSION

Abstract

Reading the Empire Survey Review of 20 years ago, with the tales of raw jungle and untrodden country, as in Sir Charles Arden-Close's retrospective accounts, I am tempted to give a brief picture of surveying in the Colonies today, away from the beaten track.     

THE EAST AFRICAN ARC

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.     

STONEHENGE AND WOODHENGE

Abstract

Owing to the kindness of the editor, I have recently been able to see the article on Stonehenge and Woodhenge by Captain Learmont, together with the editor's notes in the Empire Survey Review for April 1936. I hope the editor will also allow me space to make a few comments.     

NORMAL EQUATIONS RESOLVED BY APPROXIMATION

Abstract

We are indebted to Professor R. V. Southwell for the approximate method of computation known as the systematic relaxation of constraints. In an article to the Empire Survey Review, 1938, Mr A. N. Black showed how Southwell's ideas could be applied to the adjustment of the co-ordinates of a point.     

ELIMINATION OF ERRORS OF LATITUDE AND REFRACTION IN THE PAIRING OF AZIMUTH OBSERVATIONS

Abstract

In a previous Article (Empire Survey Review, ii, II) I described a simple graphical method for the elimination of latitude error in observations for azimuth. It was pointed out that the ideal method of adjustment of azimuths would be a simultaneous elimination of both latitude and refraction errors and, with that in view, a purely theoretical method of such an adjustment was demonstrated in the last paragraph of the article. It has now occurred to me that a fairly simple mathematical solution is possible.     

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.     

DIRECTIONS AND ANGLES IN A SIMPLE CHAIN

Abstract

Mr. Rainsford's article on “Least Square Adjustments of Triangulation: Directions versus Angles” in the Empire Survey Review No. 78, Vol. x, October 1950, leads to many speculations and interesting results. I try to show here, how, by assuming artifices to simplify the results, weights may be assigned to angles derived from directions so that the results of adjustment by angles, with these weights, will be the same as the adjustment by directions, all of equal weight.     

A TEST OF AUTO-COLLIMATION

Abstract

In the July 1940 issue of the Empire Survey Review Mr A. V. Lawes contributes a valuable article, “The Application of the Gauss Method of Collimation to the Adjustment of Survey Instruments”. One section of the article describes four methods of adjusting collimators at solar focus, in other words of assuring that the emitted rays are parallel or that the target appears at an infinite distance. Mr Lawes rightly claims that auto-collimation is the most accurate of the four methods, and he warns readers that “the reflector used in this method must be as perfect optically as the objective”. However, he fails to give any method of testing the result obtained by following his directions, and experience suggests that auto-collimation may give a result considerably in error even though the reflector may with some justification be presumed to be good.     

THE CADASTRAL MAP

Abstract

In the Empire Survey Review for April 1934 (No. 12, pp. 382–4), the Editor has raised the question of the function of the cadastral map. As he remarks, the question is not simple, but it is easier to say what the function of the map is than to decide of what the map should consist in order that it may fulfil its function. Broadly speaking we may state that the function of the map is to record the boundaries of landed property in such a manner as not only to afford a pictorial representation but also to supply data for the identification of these boundaries on the ground when occasion requires. Apart from this the map should show the areas of properties, as this information may be required for taxation purposes.     

SURVEY IN THE GREAT WAR

Abstract

Artillery Survey.—Included in the term “Artillery Survey are two distinct problems, the first that of determining the “line” and “range” at which fire should be opened, and the second that of laying the gun in the required line. To appreciate these problems it. is necessary to know a little about the technique of gunnery, and for the benefit of those who have no acquaintance with the subject the following brief résumé may be given.