Most elevation datasets are processed to report orthometric Orthometric Heights are typically used in surveying, hydrology, In the latter case, ellipsoidal ground height would be required to support the orthorectification process. The exterior orientation can be either orthometric (if the control for the project was generated using ground station data) or ellipsoidal (such as airborne GPS + IMU). GPS data, and for orthorectification of satellite imagery, whereas aerial photography can use either orthometric or ellipsoidal height depending on the datum used for the exterior orientation. Ellipsoidal Heights are typically used for applications based on.Generally made relative to the geoid (local sea level). (non-satellite based) surveying methods, all measurements are Relatively smooth, it includes local differences in gravity and so displays much more variation than the idealized ellipsoid. Geoid model surface the geoid approximates local sea level.Īlthough the geoid is a mathematical surface that is Orthometric height refers to elevation values above or below a Ground-based surveying) typically make all measurements relative to Used in aerial photography, lidar, and topographic radar, as well as Technologies (for example, satellite orbital positions and GPS, heavily Smooth surface, and it can vary greatly from the local sea level It is important to understand that the ellipsoid is a very AnĮxample of an ellipsoid is WGS 84, but there are many different Which approximates the shape of the earth as a spheroid. Refers to elevation values above or below an idealized surface Is ellipsoidal height and orthometric height. Ellipsoidal versus orthometric heightĪnother data attribute that the data manager needs to understand Water is NoData (since it is not ground)-For an application requiring accurate calculations of land area.įor most applications, the first case is the preferred interpretation.Water subsurface is valid-For hydrologic modeling, a civil engineer may want to know the topography of a river basin without any water present therefore, the DEM includes bathymetric data.This is typically used for orthorectification. In some cases, the water bodies may be normalized to have an elevation value of zero. Water is a flat surface-For visualizations, all lakes and oceans should appear at their normal water levels.How they’re represented generally depends on what the users will need. Water bodies can be represented differently in elevation models. This is less of an issue for elevation content that is contributing to the ground surface, because the surface can be used to fill in any gaps that may exist. This will ensure that when you view the data, you do not zoom out beyond the coarsest resolution, which would stop rendering the content. When using a LERC compression method to serve out surfaces that are not at ground level, it is strongly recommended to publish the data with all the levels of detail. You can have surfaces that do not represent the ground, such as the ozone layer, which is above the ground surface, or geological substrates, which are below the ground surface. Caution:Įlevation data, or surfaces, are mostly used within 3D views to represent the ground, such as a terrain model. Mentioned where applicable in the remainder of this workflow. This type of DEM is notĪpplicable in many organizations or applications but will be Rigorous methods and quality checks for use in hydrologic modeling, Is a special case of the DEM that has been developed according to Imagery, whereas a DSM should be used for viewshedĪ fourth representation is a hydrographically enforced DEM. Generally, the DEM is needed for orthorectification of aerial Refer to DEM data stored and modeled directly from points. Some also use the digital terrain model (DTM) term to Surface elevation is sometimes referred to as the digital surface Including buildings, the canopy of trees, bridges, and so on. The ground elevation is sometimes referred to as bare earth or baldĮarth or the digital elevation model (DEM), whereas the surfaceĮlevation is generally defined by the earth and the things upon it, Support most users: the elevation of the ground and of the surface. There are two fundamental elevation representations required to The third part walks you through the steps to manage and publish the elevation data. The second part discusses the data management plan and issues to consider. The first part is a discussion about elevation data. This workflow is divided into three parts. Before getting started with a workflow to manage and disseminate your elevation data, there are many things that you should first understand about the data.
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