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 (HmbVermG) of April 20th, 2005 (HmbGVBl. 2005, p.135). 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 fourth order, the used height network (high points (used heights)), as the last level of compression with around 2,600 height reference points, is the basis for all measurements 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. The markings of points of the height control point field are survey marks within the meaning of § 7 of the HambVermG. They may only be brought in, changed, restored or removed by surveying agencies (the Landesbetrieb Geoinformation und Vermessung and the publicly appointed surveyors licensed in Hamburg). They must not be impaired in their recognizability and usability. Anyone who wants to take measures that could jeopardize the measurement markers, in particular their firm position, recognizability or usability, must notify the competent authority in good time. If survey markers are to be relocated, the person responsible must bear the costs for this. The information on the height control points of the usage height network can be called up by anyone free of charge as "Individual proof of height control points" at www.geoportal-hamburg.de (search term "height control points"). In individual cases, it can happen that height reference points are no longer available locally or that the “individual proof of height reference points” are no longer up-to-date. In these cases, feedback is requested from the named contact person. The LGV is not liable for damage caused by the fact that the content shown, in particular the height information, is not up to date.
