253 ir. W. Baarda who undertook the greater part of the contents, very cleverly succeeded in making the results of his theoretical research subservient to practice, this guide that developed into an extensive volume has indeed more than cadastral significance. By introducing the concept of relative accuracy of points, Prof. Baarda comes to a reliable system of determination of points in an already existent field of points, in which always the accuracy of the location of the given points is taken into account. Great attention is paid to the possible and desirable accuracy of the measurement that ought to be tuned to the accuracy of the idealization of physical quantities through lines and points and, as far as data are concerned which Ought to be worked out graphically, into the accuracy of plotting. The choice of certain methods and the technical execution of the different phases are by this no longer voluntary but they always aim at reaching premised relative accuracy, adjusted to the object and to local circumstances. Great value is attached to the testing of measuring and calculation results according to modern statistical methods which greatly enhances the scientific value of this manual. Theoretical development is only possible if a clear insight in the calculus of observations can be obtained. An important contribution made to this subject is the book on calculus of observations by the late Prof. Tienstra compiled by his friends from his posthumous notes (i). The methods of transformation are evolved by research of Prof. Baarda (2) and (3). It is noticeable that all geodetic services and institutions make more use of modern instruments. Not only the methods of indirect distance measuring, (4) and (5), which among other things are applied by the Cadastral Service, but also the possibilities of the electro-optical and electronic distance measuring are studied. For some time the Hydrographic Office Royal Netherlands Navy is using the geodimeter of Bergstrand. In the period under review no new surveying instruments for general use have been developed in the Netherlands. The development of methods and auxiliary instruments for geodetic astronomy under the leadership of Prof. R. Roelofs is worth mentioning. A new oscillographic instrument, the time- signal oscillograph (T.S.O.) was designed; in it the time-signal as the chrono- metertick are made visible on the screen of a cathode-raytube. Coincidence takes place with the aid of an adjustable electronic delaying equipment (6). The well-known sunprism has also been improved (7). The application of modern aids in geodesy can also be established in other fields, among other things by research concerning the introduction of mechanical administration in the re-allotment procedure, the use of elec tronic calculating machines and the application of tele-communication in extensive measurements. In the field of the surveying technique the results of Ir. P. Richardus who applies the alignment-method by Van Heel for surveying purposes, are very remarkable. In this method the pointing at an object is replaced by pointing at an interference design that is shaped by placing certain diaphragms in front of a pointed source of light. After laboratory research at Delft he applied this method to distances till 50 km in the Australian Alps. He obtained an accuracy nearly twice as great as in the case of normal direction meas urement with the same instrument (8) and (9). Among the most important activities of the Triangulation Service (Dienst van de Rijksdriehoeksmeting) may be reckoned the primary measurements in the province of Limburg. The purpose is replacement of the first-order point Klifsberg which is threatened by the mining industry and the deter mination of some first-order points along the Dutch-Belgian frontier. However, in these measurements it has appeared that the central point Ubags- bcrg is subjected to alterations which can only be explained by assuming tectonic disturbances. Checking measurements are still going on in order to know more about this phenomenon.

Digitale Tijdschriftenarchief Stichting De Hollandse Cirkel en Geo Informatie Nederland

Tijdschrift voor Kadaster en Landmeetkunde (KenL) | 1958 | | pagina 55