Determination of Definitive Standard Parallels of Normal Aspect Conic Projections Equidistant along Meridians on an Old Map
ISBN 978-85-88783-11-9
Authors
1Triplat Horvat, M.; 2Lapaine, M.
1UNIVERSITY OF ZAGREB, FACULTY OF GEODESY Email: mthorvat@geof.hr
2UNIVERSITY OF ZAGREB, FACULTY OF GEODESY Email: mlapaine@geof.hr
Abstract
In previous research we proved that meridians are straight lines and parallels are arcs of concentric circles on the map Nuova carta geografica dello Stato Ecclesiastico by J. R. Bošković and Ch. Maire, which was published in 1755. We also proved the map was produced in a normal aspect conic projection equidistant along meridians. Knowing the map projection type is not enough. We need to know its parameters, too. In the first part of the paper, we are going to describe the procedure of determining standard parallels of the normal aspect conic projection equidistant along meridians. We propose a procedure for determining projection parameters of an old map, especially its standard parallels, if the radius of the sphere in which the map was produced in is unknown. Constant C is introduced as a ratio of constant K and sphere radius R, both of which are unknown. The procedure is illustrated on the map Nuova carta geografica dello Stato Ecclesiastico. The area represented on the map Nuova carta geografica dello Stato Ecclesiastico stretches from about 41°12'N to 45°3'N of latitude. Using this procedure, we obtained standard parallels at 41°50'N and 44°30'N of latitude. In addition, we are going to test whether the obtained standard parallels are actually standard parallels in which the map was produced. We conducted a procedure for testing values of surrounding pairs of parallels which are symmetric to the mean parallel of the mapped area. By applying the formula of the normal aspect equidistant conic projection and taking each pair of standard parallels, we calculated theoretical rectangular coordinates of the graticule and compared them with a coordinates of the graticule read from the map. By comparing these coordinates, we calculated deviations used to determine the definitive standard parallels in which the map Nuova carta geografica dello Stato Ecclesiastic has been produced.
Keywords
equidistant conic projection; standard parallels; Nuova carta geografica