høydedata

Høydedata, or elevation data, are geographic data representing height above a reference level. They are stored in raster or vector form, commonly as digital elevation models (DEMs), digital surface models (DSMs), or digital terrain models (DTMs). DEMs generally model the bare earth, DSMs include vegetation and buildings. Height can be given as ellipsoidal height (relative to the reference ellipsoid) or orthometric height relative to a geoid.

Sources include satellite missions such as SRTM (Shuttle Radar Topography Mission), ASTER GDEM, and TanDEM-X, as well as airborne and terrestrial LiDAR and stereo photogrammetry. Data formats include GeoTIFF, IMG, or LAS/LAZ for point clouds. Vertical datums adapt to national grids; commonly used geoid models are EGM96, with local adjustments in national height models. In Norway, height data are provided by Kartverket as part of the national geospatial infrastructure, and are made available through open data portals.

Applications: watershed analysis, flood modeling, urban planning, infrastructure design, telecommunications, navigation, and climate research. Accuracy and resolution vary: SRTM provides about 30 m resolution, LiDAR can give sub-meter point clouds, and post-processed products improve vertical accuracy. Data gaps occur over water and dense vegetation. Users must consider datum, projection, and scale when merging datasets.