The station pointer 12/Feb/2022 12:31:26Survey sextants in the Netherlands 12/Feb/2022 12:07:27The survey sextant outside the Netherlands 12/Feb/2022 10:22:55History of the sextant 11/Feb/2022 14:55:40Survey sextants in the NetherlandsPosted by Huibert-Jan Lekkerkerk 12/Feb/2022 12:07:27 Instruments Comments 0
The use of the sextant as a survey instrument in the Netherlands can be traced back to between 1799 and 1801 when C.R.T. Krayenhoff (1758-1840) used an Adams  sextant for the primary Dutch triangulation. The results were not very accurate  and the instrument was relegated to secondary measurements and reconnaissance . Until the early 20th century there are some references to the use in land survey, all with the addition that it is not a very accurate instrument but very useful for working around rivers and in swamp like situations.
The first Dutch survey sextant that is documented dates from 1910 and was made by Dutch instrument maker ‘de Koningh’. Instruments from this maker were widely used by the Dutch Rijkswaterstaat and Royal Netherlands Navy Hydrographic Service, possibly until well into the second half of the 20th century . However, after the second world war both these organisations switched to instruments from the renowned German instrument maker C. Plath. Most of the survey sextants supplied to these government organisations had an optional 90° prism which would attach in front of the horizon mirror to extend the angle of measurement by another 90° thus allowing the measurement of extremely large angles (albeit from 90° onwards with an attached prism only). The C. Plath sextants, as supplied in the second half of the 20th century, were generally adapted from the common navigation sextant but with an altered frame allowing for the placement of the prism and without mounting points for any filters. The sextant was still in use in the Royal Netherlands Navy in the 1970s but quickly gave way to electronic positioning systems .
From the 1960s onwards many major dredging and construction projects were executed that required more and more accurate positioning. A brand often used with Dutch dredging companies was Observator who supplied their sextants either with a built-in prism of special construction or as a regular sextant. These sextants were often used for the slightly less demanding projects where electronic positioning systems were in use for the more accurate positions. It is not entirely clear when electronic positioning became the sole positioning systems on these construction projects, but it is documented that the Dutch Rijkswaterstaat used the sextant until at least 1978  and the dredging industry until 1982 .
-  D.K. Bloemendaal, Krayenhoff (1758-1840), in: Orgaan der Vereniging TAK, 1958, p. 2
-  J.D. van der Plaats, Overzicht van de graadmetingen in Nederland, Tijdschrift voor Kadaster en Landmeetkunde, 1889, p. 227 ff.
-  N. van der Schaaf, Historisch overzicht van het driehoeksnet van Krayenhoff, Nederlands Geodetisch Tijdschrift, 1972, p. 69
-  A. den Boer, Sextant van Zuiderzeewerken, De Hollandse Cirkel, 2017-2, p. 76
-  N. Ferwerda, De Hollandse Cirkel 2020-04, p. 174-175
-  W.J.H. IJzereef, Digitaal Kaarteren... tovermiddel?, Geodesia, 1978, p. 7
-  M. Hooijberg, Plaatsbepaling op zee in de Pulau Tujuh Archipel, Geodesia, 1982, p. 82
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