LONG LINES ON THE EARTH: VARIOUS FORMULAE

Abstract

Extensions were given for all these formulae, so that precise results may now be obtained even for lines of 500 miles in latitudes above 45°. The present instalment gives the extension of the Clarke approximate (sic) formulae to lines of 500miles, with a practical example and general conclusions: the great advantage of the method is that 8-figuretables sufficeto give rigorous results.     

THE GEODETIC LEVELLING OF CEYLON (1926–1929)

Abstract

The Net.—The total length of the lines of the level-net is roughly 2400 miles. The net comprises 27 circuits with perimeters varying between 74 and 268 miles, and is generally closer in the wet zone than in the sparsely populated and undeveloped dry zones. In 12 circuits there are differences of level exceeding 1000 feet. The highest point reached in the net is 6572 feet, and a branch line runs from Nuwara Eliya to the summit of Pidurutalagala, the highest mountain in the island (8282 feet).     

LONG LINES ON THE EARTH : VARIOUS FORMULAE

Abstract

The use of radar has already begun to revolutionise the science of surveying. It requires the computation of lines on the earth between a hundred and a thousand miles long for the fixation of topographic control.     

MAPPING OUT OF CROWN LANDS IN CEYLON

Abstract

The Island of Ceylon has an extent of 25,332 square miles, and a population of nearly seven millions; the range of latitude is from 5° 55′ to 9° 50′ North and of longitude 79° 42′ to 81° 53′ East.     

SOME PROBLEMS OF RESECTION AND COUNTERSECTION—II

Abstract

There are numerous possibilities in a Six-point Countersection. The example exhibited in Fig. 5 shows no more than one such concatenation. Here two stations, A and B, are the, only known positions in the neighbourhood; but they are over 29 miles apart and are not mutually visible.     

A THREE-MILLION-ACRE TITLE SURVEY

Abstract

A Brief account of a survey, recently completed by me, of a block of land situated in Northern Rhodesia and some 3,000,000 acres in extent, may be of interest. The sketch-map opposite shows the geographical situation and.exterior boundaries of this block of land. It is seen that it stretches along the entire length of the Northern Rhodesia-Tanganyika Territory border, which is approximately 150 miles in length.     

THE APPLICATION OF RADAR TO SURVEYING

Abstract

Radar can be applied to surveying for precise measuren1ent of long lines, and as a navigational aid and position-fixing device for an aircraft performing a photographic survey. Trials of the radar method have recently been carried out in Australia using a modified “Shoran” equipment. The results of a large number of radar measurements of six distances, varying from 160 to 310 miles in length, indicate that an accuracy of 7 parts in 10⁵ can be achieved. Equipment errors constitute the immediate limit to accuracy, but reasonable modifications would yield a figure of 2 parts in 10⁵. Radar measurements can be completed in a fraction of the time required by normal ground survey methods, since a measurement of upwards of a hundred miles is made in a single step.

As an aid to photographic surveying a straight-line track indicator actuated by data from the “Shoran” equipment has been designed and flight tested. Its performance enabled a pilot taking aerial photographs to keep the aircraft to within an average departure of less than 0.02 mile from any desired straight-line flight path.     

RANGE FINDING WITH A THEODOLITE AND SHORT BASE

Abstract

In survey work connected with Seismic (Geophysical) investigations, the nature of the operations is such that provisional points many miles apart have frequently to be located with a minimum of delay. When no map and no triangulation exists, the range finding method about to be described is very useful. The method can also be recomlnended for reconnaissance and exploration surveys. It was used by one of the R.A. Survey Regiments with success during the war. The essentials are a good theodolite and a steel tape.     

LAND TENURE IN CANA

Abstract

The Dominion of Canada has an area of 3,695,189 sq. miles, nearly as large as the whole of Europe. It includes nine provinces, in six of which the cadastre (legal survey) has been laid down under different systems of survey, and only the remaining three under the comprehensive Dominion Lands System of Survey.     

FIRST-ORDER TRAVERSES IN CEYLON

Abstract

In the last three years about 250 miles of “precise” traverse have been surveyed in this country to provide control for detail surveys. A brief account of the results may be of general interest. The traverses are situated where trig. points are far apart, and the cost of subsidiary triangulation would have been excessive on account of the flat nature of the country.     

NOTES ON GEODETIC WORK IN THE GOLD COAST

Abstract

The Gold Coast, including that portion of Togoland which is mandated to Great Britain, comprises an area of 91,843 square miles lying between the parallels 4° 45′ N. and 11°N. and the meridians 1° 10′ E. and 3° 10′ W. The greater part of the southern area is covered with dense forest, but in the north the forest gradually opens out to more open “orchard-bush”, while in the extreme north the country consists of rolling plains covered with tall elephant-grass.     

GRID BEARINGS AND DISTANCES ON THE CONICAL ORTHOMORPHIC PROJECTION

Abstract

When computing and adjusting traverses or secondary and tertiary triangulation in countries to which the Transverse Mercator projection has been applied, it is often more convenient to work directly in terms of rectangular co-ordinates on the projection system than it is to work in terms of geographical coordinates and then convert these later on into rectangulars. The Transverse Mercator projection is designed in the first place to cover a country whose principal extent is in latitude and hence work on it is generally confined to a belt, or helts, in which the extent of longitude on either side of the central meridian is so limited as seldom to exceed a width of much more than about 200 miles.     

NOTES ON THE BASE LINES OF THE CEYLON TRIANGULATION

Abstract

The 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.     

A RESECTION METHOD

Abstract

This is a variation of the well-known device of successive approximations. It was first used by the writer about 15 years ago on a Seismic (Geophysical) Survey when resections were continually employed to locate Shot Points and Geophonestations set on arcs of 10 to 15 miles radius. Speed was an important factor, and the normal text book methods of resection were very tedious. As far as is known the method is original. It is now used by many surveyors, and the writer trusts it will be of use to others. The method is easy to remember as it has no set formula and does not involve any elaborate geometrical construction.     

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).     

THE SURVEY FRAMEWORK OF NIGERIA

Abstract

The vertical framework of Nigeria comprises a network of primary instrumental levels and trigonometrical heights. The primary levels consist at present of (1) a network in the South-western Provinces, (2) a continuous line of levels from Lagos through Ibadan, Ilesha, Akure, Benin, Onitsha, Awka, Okigwi, Aba, and Port Harcourt to Bende in Calabar Province, and (3) a further line from Ilesha to Oshogbo and thence along the railway to Minna, where it is connected to L41, the south terminal of the Minna base. The total mileage of double levelling is 1,128 miles. Trigonometrical heights have been determined by reciprocal observations over all the primary chains.     

THE RADIAL LINE ASSUMPTION

Abstract

It is very many years since the Radial Line method was first used in America and England, and, so far from going out of favour, as was predicted by some European surveyors, it is now thriving in the Slotted Template form. The history of the method is an example of the Anglo-Saxon genius for persevering in a practical compromise. Had we been tempted by the voices of the photogrammetric Rhine Maidens to adopt theoretically exact methods to solve all problems, virtually no new mapping would have been carried out during World War II and many thousands of square miles of sparsely populated territory in the U.S.A. and British Commonwealth would still remain unmapped. A much greater mapped area is associated directly or indirectly with such names as Bagley and Hotine than with others more familiar at international conferences.     

SOME SURVEYS OF RIVERS IN CEYLON

Abstract

The city of Colombo, capital of Ceylon, is situated at the mouth of the Kelani Ganga and about 25 miles north of another considerable river, the Kalu Ganga, which enters the sea at Kalutara. Though its proximity to two of the largest of the perennial rivers of Ceylon provides some advantages of inland water transport by river craft, it also places it in the zone of periodical floods which cause damage to buildings, communications and agriculture within the city limits and over extensive areas of low-lying paddy fields and gardens beyond. Except for a spur of high land running roughly parallel to the eastern shore of the harbour through Hultsdorp, Blomendahl and Kotahena to the loop of the Kelani Ganga near its mouth, the greater part of the city is very flat and only a matter of 20 feet elevation above sea-level. On its eastern flank lies a series of connected shallow lakes, marshes and paddy fields which extend in a loop from the banks of the Kelani Ganga at Ambatalenpahala to Dehiwela on the city's southern limit; there are, in addition, canals through this area with two outlets into the sea at Wellawatta and Dehiwela. Navigable canals connect the Kelani Ganga with the Beira Lake and Colombo Harbour and, with the canals already mentioned, form a continuous waterway which, in fact, extends northwards as far as Puttalam, 80 miles from Colombo, and southwards to the Kalu Ganga and Kalutara. About half a mile east of Mount Lavinia another series of shallow lakes, marshes and paddy fields spreads its irregular shape roughly parallel to the coast through the Bolgoda Lakes to a low ridge north of the Kalu Ganga and close to its right bank. The whole of these lowlands is referred to as the Bolgoda Basin. A canal called the Kepu Ela, constructed by the Dutch during their occupation of Ceylon, passes through it to join the Kalu Ganga at Diyagama about 5 miles from the river mouth.     

SOME PROBLEMS OF RESECTION AND COUNTERSECTION-I

Abstract

“A Well-Defined mountain, though miles inland and never visited by the surveyors, will often prove the very keystone of a chart which cannot be regularly and theoretically triangulated” (“Hydrographic Surveying”, by Rear-Adm. Sir Wm J. L. Wharton, K.C.B., and Rear-Adm. Mostyn Field, F.R.S. 3rd Ed. 1909, p. 128). To many the reasons prohibiting the occupation of inland stations may be unknown; it may suffice to state that, in the past, British hydrographers have mapped many coastal waters where penetration of the land was at least inadvisable. Since the charts so made were in general sold to the world, seamen of all nations have benefited from the surveys.     

THE YEAR 1931 IN NORTHERN RHODESIA

Abstract

In the survey world of Northern Rhodesia the most notable event in 1931 (apart, of course, from the birth of this Review) has been the completion of the aerial survey contracts undertaken for the Government by the Aircraft Operating Company. The results have justified expectations particularly with regard to the mapping of 63,000 square miles of the Territory on a scale of 1/250,000. Used in conjunction with the information obtained by ground methods by the Mining Companies, who have kindly consented to put their information at our disposal, a really reliable detailed map of a considerable portion of the Territory should be obtained. The mosaics of the six principal townships are also proving of value and contain a wealth of detail which would be difficult to obtain so accurately by ground survey except at great expense. On the other hand it is obvious that it would be a costly business involving a very large amount of ground control to prepare a closely contoured plan such as is required for detail purposes in connection with township lay-outs.