HISTORICAL MAPPING BACKGROUND
In South Africa the production of topographic maps is the responsibility of National Geo-spatial Information, Mowbray. Although there are records of surveying and mapping activities from the time of Van Riebeeck, surveying on a scientific basis only got under way in the late 19th century. The initiator was Sir David Gill, the then Astronomer Royal at the Cape, who in 1879 drew up a comprehensive scheme for the proper survey and mapping of South Africa. The need for accurate maps had been sorely felt for many years. Large parts of the Colony had not been mapped at all, and the few maps available were either sketch maps or grossly inaccurate.
The production of maps in South Africa has since the earliest days been intimately bound up with the system of land registration, whereby the position and extent of all land as originally ceded by the government is shown. When the Dutch East India Company established itself at the Cape of Good Hope in 1652, the Company first assigned land without having it surveyed. As more burgers came to settle the disposal of land became systematic and a Land Registry on the model of that which had long been in use in the Netherlands was established. Every Title Deed of a grant of land was accompanied by a diagram showing its boundaries and area. The shape of many of these areas was roughly circular. The radius was obtained by pacing from a walk, some 750 Rhineland roods (about 4km).
The grant of land was not fixed by survey. When obtainable it was a recognisable natural object, and if there was none then the homestead or its intended site was taken as the center. This system gave rise to many abuses and it was not until 1813 when Sir John Cradock was governor and Commander of the forces in the colony that improvements were attempted. He issued a Proclamation converting Loan Tenure into Perpetual Quitrent which necessitated a resumption of surveying and framing of diagrams. Although it was a step in the right direction subsequent surveys were undertaken in a haphazard and careless fashion. Maps were compiled by fitting together diagrams on a trial and error basis and imagination, guesswork and blatant ommission were the compiler's tools in getting the pieces to fit.
"Mr A De Smidt, Surveyor-General of the Cape from 1873-1890, describes the state of mapping in his annual report of 1876: 'From surveys, from military sketches with the plane-table, the pocket sextant, and pacing, and paid for at the rate of eight pence per square mile, and from haphazard guess work of such a description that most of the towns and villages of this extensive Colony occupy places on the published maps utterly irreconcilable with their position in latitude and longitude."
Mapping was in an unsatisfactory state towards the end of the 19th century and this explains the urgency with which Sir David Gill pressed ahead to commence the primary triangulation of the country on which all future mapping could be based. Although the triangulation progressed the production of maps proceeded slowly, due mainly to lack of funds. Pleading for more money for the completion of the triangulation MrJ.J. Bosman wrote in his annual report of 1905: 'it is beyond question only by means of the above mentioned system (i.e. triangulation) that land surveys can be placed on a satisfactory basis, that disputes over farm beacons, which often lead to litigation and dissatisfaction, may be prevented, and that the necessary data can be provided for the construction of topographical and geological maps, which are among the first requirements of civilized administration......'
Surveyors revise map of the Union Cape Times 1952
Last year men of the Trigonometrical Survey Office at Mowbray, traveled 150,000 miles to complete the revision of the topographical map of the Union. Printed in 21 sections, on a scale of 1 to 500,000. 14 sections have been published and the remaining seven will be soon. Experts in the survey office are revising the four sections of the 1 to 25,000 map of the Peninsula, and are adding new roads and built-up areas. An official of the office said, today : "Last year we surveyed about 8,000 square miles of South Africa and produced 32 maps. This year we hope to cover at least 10,000 square miles."Additions Needed "The new maps of the Peninsula will not be ready for some time."
"The trouble in mapping an area like the Peninsula is that it is impossible to produce a map right up to date. By the time the map is printed the built-up areas have been added to and revision is necessary."
"We try to anticipate future developments. We know broadly what the lay-out of the roads on the new foreshore is going to be so they will be shown on the new map. The field check of the drawings will result in the very latest development of the national road from Paarl being incorporated."
He said that primarily maps made by his department were for surveyors, soil-conservation experts and engineers.
Accurate topographical maps are indispensable to the government, to engineers, to land surveyors, to students in geology, to owners of property, and to the public in general. They are also a military necessity.
The political union of the four provinces in 1910 did not bring with it any immediate improvements. The Surveyors-Generals continued to operate independently of each other and maps continued to be inaccurate and unreliable. By 1920 the dissatisfaction over the lack of accurate topographic maps and the existing survey system was so acute that the government appointed Dr van der Sterr as Director of Trigonometrical Survey. Probably at the insistence of Dr van der Sterr, a Commission, under the chairmanship of Sir Curruthers Beattie, was appointed to enquire into the question of surveying. The outcome of the Commision's labours was the Land Survey Act of 1927, which makes provision, inter alia, a Survey Board, which would be responsible for the official surveying and mapping of the country.
THE PLANE TABLE
Every prominent feature of the landscape was measured by the theodolite with reference to the trigonometrical survey beacons, which in their turn were set with such incredible accuracy that the error over hundreds of kilometers was only a centimetre or two ! Contours on the ground were put in with the aid of that ingenious instrument the plane table – a portable table carrying a movable "sight" like a gun. The "sight" was aimed at various prominent features of the landscape and the angle was automatically marked off on a sheet of paper attached to the table. When the field work was finished the mountain of diagrams and note books with angular measurements were taken to the office where the huge task of "plotting in" the particulars of the map begun.
In 1936 the geodetic and primary triangulation had reached a stage where it covered the main developing areas of South Africa and was awaiting the practicing land surveyor to fill in the secondary triangulation. The procedures for the reconnaissance, beacon-building and observing had reached an advanced state and technical instructions had been written to enable the practicing land surveyor to play his part in doing this work whenever money was available. The tertiary triangulation was progressing slowly and a start had been made with the precise levelling. Some thought had also been given to making a start on town surveys and magnetic surveys and it was time that the topographical surveys got under way. This was the legacy left by Dr. WC van der Sterr.
An aspect of the influence of maps is the tendency of the general public to assume that when a name appears on a map it is correctly spelt and positioned. At times this is far from the case, although it is an attainment aimed at by all official mapmakers. Engineers and surveyors making plans for local use as against general and national use do not normally appreciate the problem and usually cannot be bothered whether a name is correct or not, provided it assists in the location of the object. When working on a national map series the accuracy of position and spelling becomes of paramount importance, as it is held to be authoritative by the normal map user. It was soon after World War II that the Cartographic Branch of Trigsurvey, under the able direction of N.G. Huntly, became aware of the slackness in the naming procedure on all maps being prepared by Trigsurvey. In an effort to correct this weakness Huntly suggested that all place names appearing on all maps produced by Trigsurvey should have the blessing of the Place Names Committee. The Place Names Committee (PNC), as it was then constituted, was formed in December 1936 at the request of the South African Railways and the Department of Posts and Telegraphs for the purpose of standardizing the spelling of names of railway stations and post offices. The PNC was sympathetic but, realizing that this could multiply their work enormously, agreed provided the administrative procedures were run by Trigsurvey. This meant that every place name in the whole country had to be processed. The enormity of the job was not fully realized at the start, and as the production of Trigsurvey increased, so did this work. It should be realized that for the PNC to accept a name they required evidence, and this evidence had to be supplied by the field staff of Trigsurvey. The different languages in this country meant that the field staff were required to study this academic discipline and become linguists quite apart from their technical qualifications, and this in itself was an added strain on field staff and the cause of a decided slowing down in the pace of field-work.
(extract from The Topographical 1:50 000 Map Series of South Africa by P W Thomas Retired Deputy Director-General of Surveys, Newlands)
In 1934 a Central Mapping Office was established as a separate entity at the office of the Surveyor-General of the Transvaal in order to expedite the national mapping project. However, it never received official backing and lack of personnel and equipment prevented it from making any meaningful contribution. In 1936 the office was incorporated into the Trigonometrical Survey Office and became by extension the Cartographic Branch.
In 1928 the mountainous areas of the Cape Peninsula were mapped with contours at 25 ft vertical intervals using terrestrial photography followed by stereoplotting procedures undertaken in Germany. This photogrammetric mapping formed an integral part of an excellent series of 4 sheets 1:25 000 Cape Peninsula series hand drawn under the eagle eye of Mr Pinker.
Paper prepared by P W Thomas for The Symposium – Photogrammetry in South Africa – 7 May 1981
In 1939 the first topographic maps were produced by the Trigonometrical Survey Office.
Detail S.A. Map Shows Houses, Windmills Sunday Times 19 April 1955 Sunday Times Correspondent
WORCESTER, Saturday. - The Union of South Africa is now being mapped in small detail for the first time in its history, and considerable progress has been made with this precision task which was begin in 1936. The finished product will be to a scale of 1,500 ft. to an inch. When printed for sale to the public, the scale will be 1 in 50,000. The largest existing map is on a scale of 1 in 500,000. The new 1-in-50,000 map will show minute detail, including structures such as houses in towns, windmills, dams and even mountaineers' huts perched on the peaks of the Western Province ranges. Started in 1936, the map making project was schedules as a 20-year job for completion in 1956, but there was a serious hold-up cause by the war. The immense task is being carried out by the Directorate of Trigonometrical Survey under Colonel H.A. Baumann.
Five field inspectorates are based at Worcester, Bloemfontein, Pretoria, Pietermaritzburg, and Kingwilliamstown.
Since the war the South African Air Force has collaborated with the trigonometrical men who have been supplied with tens of thousands of aerial photographs from which the bulk of the material is extracted. But field men also make ground surveys, guided by the aerial photographs.
Officials say that they have been greatly helped – particularly with regard to nomenclature – by farmers. Mountaineers to have also been of invaluable assistance.
During these years too, the work of various government departments, viz. Irrigation, Defense, Transport, Agriculture etc, was greatly hampered by the lack of reliable topographic maps. The Trigonometrical Office was busy with long term projects of compiling standard series for the whole country. Meanwhile these departments spent thousands of pounds on surveying independently in order to acquire essential topographic information. Something needed to be done urgently and the only solution appeared to be to produce a topographic map series on a reasonably small scale within a fairly short period. This task was undertaken by A D Lewis, the then Director of Irrigation, and from 1934 to 1937 the surveyors of his Department mapped South Africa on the scale 1:500 000. This series, which consisted of 10 sheets was to be of inestimable value especially as it was produced just before World War II. For many years these sheets were to be the only accurate topographic maps available of large parts of the country.
In 1936 the Minister of Lands appointed an inter-departmental committee to assist the Director of the Trigonometrical Survey Office in drawing up a detailed mapping program. The single most important contributing factor was the development of aerial photography, which made it possible to compile maps much more quickly and cheaply. These deliberations resulted in a reorganization of the office, which was from then on to be responsible for the production of all official topographical maps and aerial photographs.
New map of city and Peninsula Cape Argus 1952
The first up-to-date topographical map of the city and Cape Peninsula to be made for 20 years has been completed by the Trigonometrical Survey Office at Mowbray, and is being distributed by the Government Printer. Drawn to a scale of two and a quarter inches to the mile (1 in 25,000), the four maps which cover the area show the big expansion in the Peninsula since the last survey was made in 1932. Paarden Eiland, shown in 1932 as an almost empty space, is now a mass of red and black showing the factories.Up the Mountain The encroachment of houses up the mountainside above Green Point and Sea Point is clearly seen, as are the recent building projects in the Plumstead to Muizenberg area.
A Survey Office official said: "The revision of the 1932 map was done from aerial photographs.
"We worked in collaboration with the Mountain Club in naming all the known points on Table Mountain and with the Fisheries Department in naming all the little bays round the coast.
"An interesting technical feature of the new map is that in 1932 the magnetic variation was three minutes east a year. Now it has swung to one minute west a year."
In the years following the war the Trigonometrical Survey Office was hard pressed to cope with the demands made upon it. South Africa was expanding on a scale quite unforeseen and Departments such as Water Affairs, Transport, Post and Telecommunications etc. who were involved in the rapid development of the infrastructure of the country, all required surveys and mapping of a high order. There was a tremendous leeway to make up but the organization was fortunate in having at the helm a number of able men who were able not only to assess priorities but who were also quick to grasp the implications of technological advances and to make use of them. Today, National Geo-spatial Information has at its disposal the most modern computational and digital processing procedures available.
In 1972 the Trigonometrical Survey Office became part of a wider organisation and together with the Offices of the Surveyors-General was placed under the aegis of the Director-General of Surveys. First under the Department of Lands and subsequently part of the Department of Agricultural Credit and Land Tenure, the organization was transferred to the Department of Community Development in 1980. In June 1980 it became the Chief Directorate of Surveys and Mapping.
The Museum, van der Sterr Building, Mowbray
The museum at the office of National Geo-spatial Information in Mowbray, houses a collection of surveying and mapping instruments and artifacts which is the envy of many national mapping organisation and represents a wide range of equipment used by surveyors in South Africa over the past 150 years or more. Many of the instruments have been donated to the museum while others were used by Departmental surveyors over many years and are no longer used because of advances in technology. The instruments range in size from a pocket sized abney level with compass and bubble for measuring directions and slope angles to the massive 36 inch (914mm) diameter "Great Theodolite". There is also a full range of the Tellurometer electronic distance measuring devices which were invented and built in South Africa by Dr Wadley.
Besides an impressive range of theodolites, the museum at Mowbray also houses numerous distance measuring devices and includes a variety of chains, tapes, wires, bars and of course electronic distance measuring devices. A wide range of various models of Tellurometer instruments from the very early MRA 1 to the MRA 7 is on display in the museum.
These instruments and many more which are on display, are but a small record of the enormous amount of time and energy which the surveyors of South Africa have put in to the development of a geodetic and survey system of which this country can be justly proud and which is the envy of many more developed countries around the world. The next time you see a trig beacon on top of a mountain or building spare a thought for the surveyors who built and surveyed them and think also of the instruments which were used to accomplish this work. Perhaps a visit to the museum at the office of National Geo-spatial Information in Mowbray will increase your admiration for these hardy souls. The museum is open during normal working hours and entrance is free.
THE EARLY PIONEERS
THE ABBE DE LA CAILLE
Nicholas Louis de la Caille, French astronomer-geodist, is one of a long line of pioneers that established and molded the first South African trigonometrical survey. De la Caille was a member of the Royal Academy of Science in Paris. He arrived in the Cape of Good Hope on the vessel Le Glorieux, 150 days out from Lorient in France, on 19th April, 1751. The 38 year old astronomer, on request of Prince William of Orange, was to catalogue the southern stars by celestial co-ordinates of right ascension and declination. These observations were made from a house in Strand Street, Cape Town, owned by Mijnheer Bestbier.
Lacaille at the Cape Cape Times 11 April 1951
TWO HUNDRED years ago the Abbe De Lacaille, a brilliant young French priest turned astronomer, was sent to the Cape by the French Academy of Sciences to make a survey of the southern heavens. Although he stayed only two years, in that time he applied himself to his task with such prodigious industry and remarkable intellectual power that his contribution to the mapping of the southern skies has been a lasting one. To commemorate his visit the S.A. Public Library has made its current Quarterly Bulletin a Lacaille bi-centenary number.
His observations resulted in the cataloging of 9 766 stars and 42 nebulae. This completed, he proceeded to measure an arc of meridian over a latitude difference of 1°15′ for the purpose of ascertaining whether the shape of the earth was similar in the Southern Hemisphere to that already determined in the Northern Hemisphere. His reconnaissance was preceded by means of measuring a baseline with wooden baseline bars placed end-to-end, on ground cleared of scrub vegetation in the Zwartland, north of Cape Town. He then undertook a reconnaissance for selection of the points of his triangulation.
His findings, which indicated the earth to be less curved in the south than in the north, caused much perplexity in scientific circles for many years.
The first survey operation in this country was the measurement of a short arc of meridian in the Cape district by the Abbè de la Caille, in 1752. This was the first meridian arc measured in the Southern Hemisphere. Shortly before this the exact shape of the earth had been a subject of even heated discussions amongst scientists. According to theoretical investigations of Newton and Huygens, the earth should be flattened at the poles, a view which was corroborated by Richer's pendulum investigations.Contrary to this, the correct view, the extension of the Picard arc of meridian through France, had given rise to results which made it appear that the earth was pointed at the poles. It was in 1735 that the French sent survey expeditions to Peru and Lappland, the results of which proved finally that the earth, at least as far as the Northern Hemisphere is concerned, is flattened at the poles. In 1739 the Abbè de la Caille, together with the younger Cassini, was engaged upon a revision of the French arc of meridian ; de la Caille had also previous experience of base measurements, as he had surveyed a base of 9,353 toises on the plain of Languedoc. It will therefore not surprise us when we see that after the Abbè had completed his survey of the stars in the Southern Hemisphere, he commenced the survey of an arc of meridian between Cape Town and Klipfontein, having an astronomical amplitude of 1° 13′ 17″ in order to determine whether the shape of the two hemispheres were similar. It was then found that the length of a degree of latitude computed from his observations differed considerably from a similarly situated degree in the Northern Hemisphere, and again seemed to infer the earth being pointed at the south pole. This anomalous result was, some hundred years later, investigated by Sir Thomas Maclear, then Her Majesty's Astronomer at the Cape, who verified and extended la Caille's arc. The new arc had an astronomical amplitude of 4° 37′, and proved that the two hemispheres are similar. La Caille's astronomical amplitude was found to very nearly correct, and the anomalous result was due solely to a local deviation of the plumb line. Nearly the whole of Sir Thomas Maclear's triangulation was afterwards embodied in the geodetic survey of South Africa.
Extract of a paper read at the Cape Town Meeting of the British Association for the Advancement of Science on the 23rd July, 1929 by Dr W.C. van der Sterr
SIR THOMAS MACLEAR
Sir Thomas Maclear, Her Majesty's Astronomer at the Cape, (1834 – 79) was a surgeon turned astronomer and set about in the verification and extension of de La Caille's arc of meridian. His reconnaissance and observations took place over eight years (1840 – 48) and the results proved the similarity of the shape of the earth in the two hemispheres. It also gave the geodetic survey of South Africa an arc of meridian and geodetic control over 4°40′ of latitude from Cape Agulhas to Namaqualand. (extract from The Topographical 1:50 000 Map Series of South Africa by P W Thomas Retired Deputy Director-General of Surveys, Newlands)
He identified a new base-line near the de La Caille's original, and then taking in de La Caille's main points, established a chain of triangulation stretching northwards and southwards over more than four and a half degrees latitude. He proved that the cause of de la Caille's inconsistent result was due to a plumbline deflection.
It may not be generally known that Maclear was an intimate friend of David Livingstone, and it was to Maclear that Livingstone turned to for tuition in the use of the sextant and advice on the means of determining his position in the unmapped wilds of then " Darkest Africa ".
This triangulation was later extended eastwards along the southern coast by Captain Bailey RE (1859 – 62) as far as the Great Kei River as control for hydrographic charts.. This was a chain of triangles tied to the southern end of Maclear's arc, which extended eastward and inland off the coast for 800 km, past Mossel Bay, Port Elizabeth, East London and up to the Kei River frontier of the Cape Colony. Capt. William Bailey was also responsible for measuring a check baseline. Unfortunately, he lost many of his records when he was shipwrecked aboard the Waldensian.
The Astronomer Who Climbed Mountains Cape Times 4 November 1950
THOMAS MACLEAR turned from his tent pitched high up on an unnamed mountain in the Cedarbergen. He was exhausted having just descended the peak above him, which he had earlier climbed to make observations, and he had hoped to turn in early. But before him stood a farmer who had climbed up from the valley below. "If Mijnheer would please come down to the valley," he asked diffidently, "there are one or two women who have heard that in England Mijnheer was a doctor, and in these distant parts there is no doctor". Maclear felt he could not refuse this request, for he remembered the kindness of the farmers and their wives to him in the Khamiesberg. So, in spite of his weariness, Maclear went down to the valley and found awaiting him, not one or two sick women, but two wagon-loads of them. It was Thomas Maclear's interest in astronomy while practising as a doctor, which led to his appointment at the Cape as Astronomer Royal. Born at Tyrone, Ireland, in 1794, he was sent to England and trained as a doctor at Guy's and St. Thomas's hospitals, London. He acquitted himself brilliantly, and was appointed house surgeon to Bedford Infirmary. It was at Bedford that he met W.H. Smyth, who had a private observatory, and through him Sir Francis Beaufort. The wind velocity scale, known as the Beaufort Scale, is still used to denote the force of gales. Through his interest in astronomy at Biggleswade, Thomas Maclear became a member of the Astronomical Society and was elected a fellow of the Royal Society in 1831........ After his retirement, Sir Thomas lived at Mowbray. In 1876 he became totally blind, his eyes had been injured several years before when the dark glasses through which he was observing the sun were broken by the heat, and his eyes were exposed to the full force of the sun's rays.
........People's names are not lightly given to places in South Africa, and Cape Maclear near Cape Point, and Maclear's Beacon on Table Mountain are fitting mementoes of his untiring activities, and undaunted spirit. Mary Kuttel
SIR DAVID GILL AND COLONEL MORRIS
On 19 February 1879, Sir David Gill was appointed as Her Majesty's Astronomer at the Cape and later became honorary scientific advisor for the geodetic survey. It is he who should be regarded as the father of the present integrated survey system. The attempts at a geodetic survey up to Gill's appointment must be regarded as scientific. Gill arrived in the Colony in the midst of a controversy that was raging about the inadequacy of the existing system of cadastral surveys and the unreliability of the surveyor's diagram. This brought him face to face with the survey problem of the subcontinent. He grabbed the opportunity with both hands and recommended a strong geodetic survey and even visualized it extending through Africa to Cairo and beyond – the 30th meridian arc concept. In this he was strongly supported by the Director-General of Ordnance Survey, Colonel Cooke RE (Royal Engineer), by the Astronomer Royal in London, Sir George Airy, by that remarkable Surveyor-General of the Cape, Abraham de Smidt and by the Governor, Sir Bartle Frere.
He provided the impulse and drive that ultimately led to the extension of chains of triangulation providing a uniform framework for the Cape Colony, Natal, Orange River Colony, the Transvaal and regions beyond the Limpopo. Much of this work was undertaken and completed by Colonel W Morris RE and a party of Royal Engineers during the years 1883 to 1892. Progress was slow but sure.
About the turn of the century Sir David Gill was trying to convince the colonial and republican governments of the necessity for a well-mapped country. In 1904 he chaired a Topographical Survey Congress in Cape Town, attended by the surveyors-general and Major Close and Colonel Morris of the War Office. The recommendations of the Congress read as well today as they did then, being concerned with centralized and systematic mapping; but due to funding difficulties nothing came of the matter, except that the War Office did undertake the 1:125 000 series of the Orange River Colony and the 1:250 000 of the north-west Cape. These two series were surveyed by the Royal Engineers using plane tables and based on very sparse control. This work must be considered a major achievement considering the nature of the country, the equipment available, the control density and the transport problems involved.
(extract from The Topographical 1:50 000 Map Series of South Africa by P W Thomas Retired Deputy Director-General of Surveys, Newlands)
The real foundations for the geodetic survey of South Africa were laid by Sir David Gill, His Majesty's Astronomer at the Cape from 1879 to 1907. This country owes him a big debt of gratitude. It is to his indomitable perseverance that we are now placed in possession of an accurate "gridiron" system of geodetic chains covering well-nigh the whole of the Union, and joining up with the Rhodesian triangulation. Under his direction the work was carried out by Colonel (now Sir William) Morris, who, together with his staff, deserve our highest praise for the manner in which this great undertaking was brought to a successful issue. We are further indebted to the late Mr Bosman and the late Mr Alston, land surveyors of this country, for their contributions to the geodetic survey. Their work provided a connecting link between the northern part of Maclear's triangulation and the eastern geodetic chains.
Extract of a paper read at the Cape Town Meeting of the British Association for the Advancement of Science on the 23rd July, 1929 by Dr W.C. van der Sterr
In the year 1883 a detachment of British Royal Engineers surveyors arrived in Durban under the command of Captain Morris. The measurement of the Pietermaritzburg base with five Troughton and Simms ten-foot wood-encased steel bars, then commenced. The outcome of this ensured the extension of the chain northwards to Newcastle.
THE GEODETIC SURVEY
The geodetic survey is based entirely on the framework provided by the geodetic survey. The trigonometrical survey to date consists of a primary triangulation, having an average side of a triangle of 40 to 100 km; a secondary triangulation with sides of 10 to 25 km; and the small beginnings of a tertiary triangulation, with sides of 2 to 8 km.
THE CHANGES IN POSITIONING TECHNOLOGY
As has already been mentioned the museum at Mowbray is representative of a collection of surveying and mapping instruments which have been either donated by many surveyors or their families or are instruments which are no longer serviceable. Many of the instruments date back to the 19th century when men such as Sir Thomas Maclear, Sir David Gill, Colonel Morris and many others were laying down the foundation of the excellent geodetic system of which South Africa can be justly proud. Of all the instruments in the museum, perhaps the most impressive is the enormous 36 inch so-called "Indian" theodolite. This very impressive monster theodolite is one of five ever built and was used for the cataloguing of stars in the Southern Hemisphere in the latter part of the 19th century.
If one looks at the theodolites one sees very little major change in the design from the oldest up to those used in very recent times including the "Indian" theodolite. The basic design of mechanical-optical theodolites, i.e. a telescope mounted on uprights and capable of rotating on vertical and horizontal axes with "protractors" attached to measure vertical and horizontal angles, has changed little over the years.
Many of the protractors, or to give them their more technical term, circles, are exposed to the element if not totally at least in part. This was necessary because the external microscopes were used to read the very fine engravings on the circles. This is particularly the case with instruments designed up until the late 1920's when a major design change was introduced and which primarily affected the manner in which the circles were read.
By using a system of prisms, diagonally opposite parts of both the horizontal and vertical circles could be read simultaneously through one microscope. At the same time the circles could be totally enclosed which protected the delicate working parts from the elements.
At the same time, instead of manufacturing the circles from brass and silver and mechanically engraving the graduations, circles were made of glass and engraved using photographic etching techniques thus making it possible to greatly reduce the size of theodolites without sacrificing accuracy.
Attention should be drawn to the great evolution of survey instruments, which has resulted in ever increasing accuracy and greater speed, with corresponding lessening of cost. The Abbe de la Caille used a sextant of 6 feet radius, having two telescopes of six and a half and five and a half feet, respectively, and a quadrant of three feet radius. Sir Thomas Maclear's instruments consisted of a theodolite of 20 inches horizontal circle, made by Thos. Jones and an eight and a half inch theodolite by Reichenbach and Ertel. The instrument used by Sir William Morris was an 18-inch theodolite by Troughton and Simms, which, together with stand, iron ring and packing cases, weighed 260 lbs. The instrument alone, when packed in two cases, weighed respectively 75 and 51 lbs. The Trigonometrical Survey has been fortunate in being able to procure instruments of ever-decreasing weight, such as 8-inch Repsold, 8-inch Troughton and Simms, 8-inch Watt and Sons, 8-inch Cooke, Troughton and Simms, 22 cm. Hildebrand, while lately the survey obtained eight theodolites by Wild of the five and a half inch pattern. These Wild theodolites are great favourites with the observers, who prefer them to any other instrument on account of their light weight, their accuracy, and above all their rapidity of manipulation. The theodolite weighs 24 lbs., its case 8 lbs., and the tripod 18 lbs. The results as obtained with three Wild theodolites, by three different surveyors, on secondary triangulation, have on an average a probable angle error of 0''.36 for eight arcs, an accuracy which must be considered unnecessarily high for secondary triangulation. For trained surveyors it will be possible in future to allow a smaller number of arcs. In the case of a very experienced observer, who now observes six arcs only, the probable error of an angle, as deduced from the closure errors of 23 triangles, is only 0''.34. This equals the accuracy obtained by the geodetic survey of South Africa and Zimbabwe, using 10-inch Repsolds and heliotropes. Under ordinary weather conditions the time occupied for observing a complete arc to include four to six stations in both positions of the instrument takes, with the Wild theodolite, from 10 to 20 minutes.
Extract of a paper read at the Cape Town Meeting of the British Association for the Advancement of Science on 23 July, 1929 by Dr W.C. van der Sterr
A modern glass circled 5.3 inch (135mm) theodolite is just as accurate, if not more so, than the monster 36 inch (914mm) Indian theodolite. The term 5.3 or 36 inch theodolite refers to the diameter of the horizontal circle used on the instrument.
The Cape Argus, Saturday, August 20, 1949
On a wall on the sea side of Strand Street, flanked by a shop that sells women's lingerie and another stocking electrical equipment, is a bronze plaque with the inscription : "On this site L'Abbe de la Caille carried out his astronomical observations in the years 1751 and 1752 A.D."
The Great Indian Theodolite
Naturally, with reduction in size came a reduction in weight making it possible for one person to backpack a complete instrument to the point to be surveyed, some of which required many hours of hiking up high and hazardous mountains. Because of their size many early first order geodetic theodolites were dismantled with the upper and lower halves being carried in separate boxes. The last theodolite to be used by the Trigonometrical Survey Office which was transported in separate boxes was the Wild T4 astronomical theodolite with its 9½ inch (240mm) circle. This instrument was still used for the measurement of high precision latitude and longitude up until 1978 when four La Place stations were observed.
Practically all the triangulation which has been built up over the years from the time of Sir Thomas Maclear has been observed using mechanical-optical theodolites similar to those described above. Even as late as the late 1980's, a young surveyor joining what had become known as Surveys and Land Information would have measured many angles and directions using various types of theodolites depending on the accuracy requirements of the task at hand to determine the co-ordinates of trigonometrical beacons and town survey marks. Of all the theodolites used by the Trigonometrical Survey Office and the many private surveyors who carried out contract work for the office, the Wild Universal 3.54 inch (90mm) T2 theodolite was used extensively for the survey of many thousands of trigonometrical and town survey marks. This lightweight compact instrument was the workhorse of surveyors from about the 1930's and is still used by many where electronic theodolites are not available. It has been said that South Africa was surveyed with the Wild T2 theodolite.
Chief of the General Staff, U.D.F.Department of Defence Pretoria....
The main objection which the C.G.S. has to the South African projection system is that it is too narrow for topographical purposes and should be extended to three times the width. He is so convinced of the desirability of these 6 degree belts that he urges upon the Union Government and the Survey Authorities the advisability of changing over from the present 2 degree belts. I feel sure that the C.G.S. is not fully acquainted with South African survey conditions and requirements nor with the work which has already been achieved in this country......The C.G.S. states that the unit for the grids will be 10 kilometres, and for this unit coins the word 'decakilometre' a word which is certainly more euphonious than for instance hectohectometre which might lead to wrong conclusions over the telephone. However, it seems to me unnecessary to coin a new word when we have an official term for 10,000 metres available in the word 'myriametre'..... In conclusion I wish to express the hope that I have made it clear that the Gauss Conform 2 degree system has been chosen with the object of fulfilling the requirements of the cadastral survey both from the technical and economical standpoint. Also that in a national survey, the requirements of the cadastral survey must be regarded as paramount, and also that the economic establishment and maintenance of the topographical survey depends upon full use being made of the cadastral survey and system. Following the inspiring lead of Sir David Gill and the principle he laid down for the establishment of one united system of main triangulation net over the whole of Africa, I have aimed at laying down a co-ordinate system in the Union which will give effect to his far-seeing plan.
Extract from a letter signed Dr W van der Sterr 2nd July, 1931
Up until the late 1950's and early 1960's, most distance measuring was done using mechanical methods such as bars, wires, chains or tapes. Optical methods which involved the measurement of an angle subtended by bar of fixed length or a distance subtended by a fixed angle were also used. The former was the subtense bar and consisted of a 1m horizontal bar mounted on a tripod with a target at each end. The angle between the targets was measured from the distant point with a theodolite and by simple trigonometry the distance between the theodolite and the subtense bar could be calculated. The instrument was used very little by the Trigonometrical Survey Office and then only for the survey of town survey marks.
Up until the late 1950's, the measurement of very high precision long distances was a complex and time consuming but essential operation. A number of different methods and instruments were used for these measurements and included a variety of bars, tapes and wires. The bars that were used were generally 3m to 5m in length with finely engraved marks at each end. In order to measure the distance between two terminal points, the bars had to be placed end-to-end ensuring that the engraved marks of each consecutive bar coincided exactly. With each bar mounted on its own pair of tripods, the measurement proceeded in a leap frogging fashion taking great care to line up the bars to ensure that the shortest distance between the two points was measured. When distances were measured using tapes or wires, the tension exerted on the tape or wire was critical to the success of the measurement. The temperature of the air surrounding the wire or tape was also carefully measured to allow for changes in the measured distance caused by the expansion or contraction of the material used to make the tape or wire. In an effort to maintain a constant temperature over the entire length of the tape, wire or series of bay lengths to measured using bars, a shelter of hessian or some such material was built to shield the tape, wire or bars from direct sunlight or wind. Apart the actual measurement procedure the construction of the protecting shelter or tunnel added enormously to the time taken to measure between the terminal points of the line to be measured. Eleven such base lines (as they are termed in geodesy) were measured in South Africa from 1830 until 1957. The last base line measured using invar wires was at Otjiwasandu in Namibia in 1957 and was measured by Prof. George Menzies of UCT. Invar is a material with an extremely low coefficient of expansion.
Stereogoniometer built by Barr & Stroud in 1928 for Henry Georges Fourcade who developed the principles of modern day stereo-photogrammetry in 1902. Unbeknown to one another, C Pulfrich, who was based in Germany, developed similar principles a few months after HG Fourcade. The controversy of who should be claimed as the first to develop these principles remains to this day.
The major evolution of survey instruments and positioning techniques started in the 1950's with emergence of electronics as new technological age and the hotting up of the so-called space race between Russia and the United States of America. Around this time Dr Wadley of the CSIR started developing distance measuring devices using electronics and microwave radio techniques.
The technique entailed the use of two instruments, a master and remote, to measure the elapsed time between the transmission of a signal from the master to the remote and then back to the master. Dr Wadley developed what became known as the Tellurometer and at the same time revolutionised long range distance measuring for surveying and geodesy. The days of measuring only a few base lines using tapes, wires or bars in a triangulation network were over. It was now possible to measure each side of all triangles in the network which, together with the measurement of all angles in the network, made it possible to build an extremely strong and reliable network of triangles. It was in fact possible to build up a geodetic network using a technique known as trilateration in which only the distances and no angles between all visible points were measured. This technique was used by the Trigonometrical Survey Office in the 1960's and early 1970's in the sparsely populated areas of the Kalahari and Bushmanland.
Tellurometer Cape Argus 20 May 1957
I heard a new name today – tellurometer. A tellurometer, according to Co. H. Baumann, who invented it, (Ed. Note – he conceived the idea) measures distance by micro-wave, a departure from any other method yet used. And to think that Colonel Baumann used to measure by dragging a surveyor's chain about when he was a boy ! Colonel Baumann, who is a former, director of the Union Trigonometrical Survey, is now in the Surveyor-General's Department in Southern Rhodesia. He was in Cape Town at the weekend on his way back from England, where he saw the sensation his brain-child caused when it was demonstrated at Ridgeway Base, near Marlborough, to civil, military and naval personnel. The brasshats came in a somewhat cynical mood but were impressed by what they saw.Within inces The tellurometer was used to measure an undisclosed distance worked out by the Ordinance Survey of Great Britain. Mr Wadley, who made the instrument to Colonel Baumann's specifications told the Ordinance Survey that they had made a mistake of point six of a metre over a distance of 15 miles. When the calculation was rechecked the error was reduced to a couple of inches.
In developing the Tellurometer, Dr Wadley worked very closely with many personnel from the Trigonometrical Survey Office. Some of the first test lines were measured between the Trigonometrical beacons on the slopes of Table Mountain and on the Hottentots Holland. Over a period of more than twenty years Plessey, the manufacturers of the Tellurometer, developed many models of the instrument including the MRA1 to MRA7 range most of which were used extensively for geodetic work by the Trigonometrical Survey Office. These instruments and others in the microwave-based range of Tellurometer were used not only in South Africa but also in many other countries around the world.
An extension to the micro-wave range of electronic distance measuring, or EDM, instruments used infra-red carrier waves to measure the distance between two points. The same basic technique as used in microwave instruments, i.e. to measure the elapsed time between the transmission and reception of a signal, was used in these instruments. The major difference between the two types of EDM is that the remote instrument in the microwave pair is replaced by a special set of reflectors or comer prisms, which reflect the transmitted signal back to the instrument. The second major difference was that the maximum range, which could be measured with this type of instrument, was limited to about 2km whereas distances of 50km, or even longer under favourable conditions, could be measured conditions with the latter models of the MRA range of instruments. Numerous models or types of the Tellurometer range of infra-red instruments were used over the years by the Trigonometrical Survey Office but perhaps the most accurate but at the same most cumbersome was the MA100 which weighed nearly 17.3kg. This instrument was capable of accuracy's about 3.5mm over 1km. The MA100 was used for the survey of many town survey schemes and, until replaced in the mid-1980's, international boundary surveys. It was not only used by this office but also by many surveyors engaged on high precision engineering and slope and structure monitoring surveys.
Simultaneous to the development of the early microwave Tellurometers, a Swedish company developed an instrument known as the Geodimeter, which used light waves as the measuring medium. The Trigonometrical Survey Office used one such instrument for the survey of a few town survey mark schemes but the instrument did not fair very well under South African conditions and had to be used at night to achieve the best possible result.
Distance measuring instruments were not the exclusive domain of improvement as a result of electronics. Electronic theodolites and levels were developed use various systems of bar coding and interference fringe measurement and detection to measure angles from theodolite circles and levelling staves. Electronic theodolites have not been extensively used by the Trigonometrical Survey Office and electronic levels are slowly being introduced for levelling purposes which do not require high precision results. At present electronic level technology still cannot achieve the same results as a traditional precise spirit level with parallel plate micrometer and invar levelling staves.
In the early 1980's the Trigonometrical Survey Office purchased five Doppler satellite receivers which were used to determine the position of 24 trigonometrical beacons throughout South Africa. In addition to the points occupied in South Africa a number points were also occupied in Namibia or South West Africa as it was known at the time. The positions of 6 of these points in South Africa and 3 in Namibia were computed and added to a network of points which covered the entire African continent in a project known as ADOS (Africa Doppler Survey) in an effort to establish a uniform geodetic network for Africa. Because of the relatively wide spacing of the points occupied in South Africa, up to 300kms in most cases, the Doppler survey could only be used to identify weaknesses in the geodetic network which were caused largely by the lack of suitable baseline measurements in the original triangulation network.
GPS (Global Positioning System)
The use of the US NNSS and Doppler techniques for positioning was quickly taken over by the Global Positioning System, GPS, which was the next and perhaps most significant development in positioning technology. GPS was also developed by the US Department of Defence to meet its navigational requirements for a wide range of applications. Signals from GPS satellites were deliberately interfered with to down grade the position achievable by civilian users. Initially these users could achieve accuracy's around 1OOm but since May 2000 this has been improved and accuracy's of approximately 10m to 15 m are achievable using a single receiver. Various techniques were, however, developed to improve the relative accuracy between two points receiving simultaneous data from GPS satellites and positions with accuracy's of better than .05m are now achievable provided one of the points is located on a point of known position. In 1990 six GPS receivers were purchased by the Trigonometrical Survey Office and a project was set in motion to determine the position of 200 trigonometrical beacons of the national geodetic network in which the average distance between points was approximately 1OOkm. The project took less than two years to complete which, if the traditional theodolites and EDM instruments had been used, would have taken at least five times longer and then only if adjacent points were intervisible. It was this project which became the foundation of the recomputation of the South African co-ordinate system on a modern reference figure of the Earth.
With the introduction of satellite based positioning techniques, and especially GPS, to the world of geodesy and surveying, the use of long range micro-wave EDM instruments and first order theodolites has become obsolete for geodetic purposes. The positions of well over 1000 points have been determined in recent years using GPS techniques exclusively and it is doubtful that young surveyors with less than 10 years experience even know how to use micro-wave instruments and first order theodolites let alone astronomic theodolites.
GPS has changed the manner in the way geodisists and surveyors carry out their work. It has also changed the philosophy surrounding national control survey networks not only in South Africa but in many other countries around the world. The network of trigonometrical beacons on tops of mountain and tall structures and buildings is known as a passive network since the beacon merely represents the position of the co-ordinate assigned to it and plays no role in updating or monitoring its position. In contrast, the current thinking lies in the establishment of active control survey networks (TrigNet) which utilises GPS as the primary positioning tool. TrigNet is a network of continuously operating GNSS base stations covering South Africa all managed and controlled by a single control centre situated in the offices of National Geospatial Information (NGI). The first stations in the network were installed in 1999 and now consist of almost 60 operational stations. The stations have been set up on Municipal and Provincial offices, manned weather stations, airports and other such facilities.
Surveying techniques and the design of instruments changed little from the time of Sir Thomas Maclear up until about the late 1950's when electronics started to have a major impact on instrument design. The launching of the Russian Sputnik satellite heralded the dawn of a new era in positioning to the extent where GPS is the primary positioning tool of many surveyors. GPS has also resulted in a radical change in philosophy with respect to the establishment of national control survey networks. During all these changes and advances in technology the Trigonometrical Survey Office adopted the new technologies and adapted its measuring procedures accordingly and has led the way in which surveyors go about their work in South Africa. In spite of the modern technology and the ease with which the position of points can be determined, the application of sound basic principles of surveying and geodesy remain at the core of the office's procedures to produce high quality co-ordinates and heights thus satisfying the needs of surveyors, engineers, planners, geographers and so on.
The New South African Datum is referred to as the Hartebeesthoek94 Datum and uses the World Geodetic System 1984 (WGS84) as ellipsoid of reference. The datum was implemented nationally on 1 January 1999.
The Hartebeesthoek94 Datum enables South Africa to retain its status of possessing one of the most up to date and advanced integrated survey reference systems in the world, which affords its users the freedom to integrate their geo-spatial data in the world arena. The new datum also provides South Africa with the opportunity to assist its southern African neighbours with technical and technological expertise in upgrading their geodetic.