engleski

Problems in Standard Parallels Reconstruction

In a 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, 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. So in addition of research, we proposed a new procedure for determining standard parallels of an old map, of the normal aspect conic projection equidistant along meridians, if the radius of the sphere which is mapped is unknown. We calculated that probable standard parallels in which the map was produced are at and of latitude. Furthermore, we proposed a procedure for testing reliability of standard parallels on the old map. The procedure resulted with the conclusion that the determination of standard parallels is not an easy task. In this paper, we examine whether our assumption, that the map was produced in the normal aspect conic projection equidistant along meridians, is correct. We calculated rectangular coordinates for pairs of parallels at intervals of 10' which are symmetrical in relation to the central parallel in the map area for equal-area, conformal, equidistant along parallels and equidistant along meridians normal aspect conic projections. The final decision on the map projection used is based on a comparison of calculated average values of deviations between theoretical and depicted graticule on the map. Considering that the curved Earth's surface cannot be mapped into a plane with a distortion equal to zero, the influence of distortions can be significantly reduced by selecting the most appropriate standard parallels. Distortions are more pronounced on small scale maps. In the last part of the paper, the procedure for determining of the bandwidth in which influence of standard parallels is more pronounced is described.

old maps ; map projections ; conic projections ; standard parallels

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