George Tyrrell McCaw, geodesist, was educated at Lurgan College and at Trinity College, Dublin (University of Dublin), graduating in arts and in engineering in 1893. He had a strong aptitude for science and mathematics and was awarded the degree Master of Arts (MA) in 1908. From 1893 to 1903 he was employed in the General Valuation and Boundary Survey of the Irish civil service. In October of the latter year he came to southern Africa and, after six weeks training in observational astronomy at the Royal Observatory in Cape Town, became chief assistant to Dr T. Rubin*, who was conducting the geodetic survey of Northern Rhodesia (now Zambia), including the measurement of a geodetic arc along the 30 degrees East meridian, under the direction of Dr David Gill*. [See Rubin's biography for an account of this work.] Many years later McCaw prepared for publication the Report on the measurement of the thirtieth meridian in North-Eastern Rhodesia (1933).
After leaving southern Africa in June 1906 McCaw assisted Rubin in the measurement of a baseline in Sweden. In 1908 he went to Uganda, where the Anglo-Congolese Boundary Commission had conducted a topographical survey of the western frontier. Major E.M. Jack, a member of the commission, remained behind to survey another portion of the arc of meridian and with McCaw, who supplied the technical knowledge, carried out the geodetic triangulation during 1908 and 1909. Soon after the completion of this work McCaw went to Fiji in 1910, where he carried out the primary triangulation of the islands from 1911 to 1915. His report on the work was published in two volumes in 1917. That same year, during World War I (1914-1918) he was commissioned with the rank of captain in the Royal Engineers under Jack (by then a colonel), who was in charge of map supply and survey work at General Head Quarters in France. In this position McCaw was confronted with a number of novel problems connected with map projections and trigonometrical adjustments and made a notable contribution to their solution. His work was so highly regarded that after the war a special post was created for him in the Geographical Section of the General Staff (in the War Office). He remained there until his retirement in 1936, his main task being the application of military grids to the triangulation systems and map projections of foreign countries. However, he also worked on the mathematical problems of air photographic surveying and was secretary of the Air Survey Committee from its formation in 1921 to his retirement. Among others he worked on the design of the first air-photo plotting machine produced in Britain. He also played a leading role in the organisation of the conferences of Empire survey officers and in 1931 became the first editor of the Empire Survey Review.
Several papers by McCaw were published in early volumes of the South African Survey Journal: 'Note on the Snellius problem' (1925, Vol. 1(7), pp. 360-362), 'Determination of the division errors of a circle from the measures of a triangulation' (1927, Vol. 2(5), pp. 219-224), 'Long logarithms' (1927, Vol. 2(6), pp. 279-283), 'Caswell's three problems' (1928, Vol. 3(17), pp. 10-21), 'Air survey in practice' (1929, Vol. 3(21), pp. 186-193), and 'The African arc of meridian' (1931, Vol. 4(27), pp. 53-57; 1932, Vol. 4(28), pp. 93-97; and 1933, Vol. 4(30), pp. 182-187). Other publications by him included Approximately rigorous adjustment of simple figures (HMSO, 1919, 53p), 'A modified rectangular polyconic projection' (The Geographical Journal, 1921), 'The proposed adoption of a standard figure of the earth' (Ibid, 1924), and several contributions to the Empire Survey Review.
McCaw was honoured as an Officer of the Order of the British Empire (OBE) in 1927, as a Companion of the Order of St Michael and St George (CMG) in 1936, and as an honorary member of the Institution of Royal Engineers. Although he was a leading authority on geodesy and surveying in general, he was a modest man, had a genial personality and made many friends among his colleagues.