Wherever precise height information is required, height reference points have always been used for surveying tasks and solutions in the context of building surveying, map production and national surveying. The height control points serve in their entirety for the physical realization of the height control point field and thus the height component of the geodetic spatial reference in the sense of § 2 paragraph 2 of the Hamburg Law on Surveying of April 20th, 2005 in the area of the Free and Hanseatic City of Hamburg (FHH). The height values are given in the official height reference system of the German main height network as normal heights in "meters above normal height zero" (NHN). The associated coordinate reference system (CRS) has been DE_DHHN_16_NH since December 1st, 2016, the height horizon of which is 14-17 millimeters lower than the values of the CRS DE_DHHN_92 from 1992 valid until November 30th, 2016. The height control point field of the FHH consists of hierarchically structured height networks of the 1st to 4th order. While the first three orders serve to ensure the height reference, the IVth order, the recording height network, as the last consolidation level with around 2,600 height reference points, is the basis for all private-sector surveys with official height reference. The height control points are determined by the state office for geoinformation and surveying using geometric leveling and at a point spacing that is appropriate to each other. The last area-wide review or re-determination of the height values took place in 2010. If necessary, individual re-measurements take place. The height is given in millimeters. Metal bolts on house facades or bridge foundations are mainly used as permanent markings. In peripheral areas with little development z. B. granite or concrete stones introduced into the ground form the basis for markings. * Important note on dealing with survey marks: Survey marks for marking points of the height control point field may only be introduced, changed, restored or removed by surveying bodies (these are the state office for geoinformation and surveying and the publicly appointed surveyors licensed in Hamburg)!
