Height Reference for Parcels and Land Objects for the 3D Cadastres Structuring

This paper describes the distinct existing systems to reference the height of objects and its possible applications in the structuring of 3D cadastre. It discusses advantages and inconveniences in the utilization of each one of them for the positioning of terrestrial objects in space. Hypotheses based on similar studies of cases in 3D cadastre are analyzed, without the pretension of covering the totality in the same manner. The developed theory is applied to position apartments that are part of private residential buildings (3D parcels) and elements of road work (3D land objects), demonstrating the correlations between the distinct systems of heights. It is possible to conclude from the results that the ellipsoid of revolution is the most appropriate reference surface for 3D parcels and generally all 3D land object heights. Furthermore, for certain territorial 3D objects, it may be necessary to utilize an equipotential surface to reference their heights. Regarding the precisions required for the positioning and sizing of the plots and 3D objects, it is concluded that both must be carefully analyzed and defined in the cadastral legislation. It is not possible to set a single precision for all, parcels and land objects, since the accuracies depend of the function of the cadastral object