Delft, 1975. 39 pagina's.
ISBN-13: 978 90 6132 222 1. ISBN-10: 90 6132 222 7.
At the end of the 19th century astronomical observations were carried out in The Netherlands with the object of establishing a reference ellipsoid for the national triangulation. For this purpose latitude and azimuth were determined in 13 first order points, regularly distributed over the network. The methods applied for these determinations were meridian altitudes of stars (latitude) and Polaris observations (azimuth). Starting from the astronomical data obtained in each of these points and using the geodetic data of the network, 13 values for latitude and azimuth were computed for Amersfoort, the central station of the net. The mean of these 13 values was assumed to be the geodetic latitude of Amersfoort and the azimuth Amersfoort-Utrecht
The longitude of Amersfoort, although less important for the ellipsoid, was derived from the longitude of Leiden and from the longitude difference Amersfoort-Leiden, computed from the geodetic data. The data of Amersfoort obtained in this way are:
latitude j = 52°09'22".178
longitude l = - 5°23'15".500
azimuth Amersfoort-Utrecht A = 248°35'19".891
Laplace stations for azimuth control were not used in the adjustment of the network. In a small country like The Netherlands this is admissible. The need for Laplace stations came much later, namely after the second world war, when it was decided to readjust the European network as a whole. Three twin Laplace stations were planned in The Netherlands for this purpose, i.e. Leeuwarden-Ameland, Zierikzee-Goedereede and Ubachsberg-Tongeren. The measurements were carried out using the following methods:
- Longitude determination by meridian transit of stars. Leeuwarden (1947), Ameland (1947), Zierikzee (1949) and Goedereede (1950); see section 3.
- Simultaneous determination of latitude, longitude and azimuth using the Black method.
Ubachsberg (1968), Tongeren (1968); see section 4.
- Azimuth by Polaris. Goedereede (1969), Zierikzee (1973); see section 5.
In addition some results from older measurements are available:
- Azimuth by Polaris and some circumpolar stars. Ubachsberg (1893).
- Determination of the longitude difference Leiden-Ubachsberg (1893).
- Azimuth by Polaris. Leeuwarden (1 897), Ameland (1 897), Zierikzee (1897).
List of symbols 4
- Introduction 5
- Instrument set-ups, reductions to centre, polar motion correction 6
- Longitude determinations (Leeuwarden, Ameland, Zierikzee, Goedereede) 8
- Simultaneous latitude, longitude and azimuth determinations (Ubachsberg, Tongeren) 15
- Azimuth determinations (Goedereede, Zierikzee) 19
- Misclosures of the Laplace stations 22
- Data longitude determinations 27
- Data simultaneous latitude, longitude and azimuth determinations 32
- Data azimuth determinations 36
- Systematic errors in the circle division of the theodolite DKM 3A No. 134824 39
- Covariance-matrix of the coordinates related to the base Amersfoort-Veluwe 39