NOAA VDatum Conversion

VDatum is designed to vertically transform geospatial data among a variety of tidal, orthometric and ellipsoidal vertical datums - allowing users to convert their data from different horizontal/vertical references into a common system and enabling the fusion of diverse geospatial data in desired reference levels. This particular layer allows you to convert from NAVD 88 to MHHW. Units: meters These data are a derived product of the NOAA VDatum tool and they extend the tool's Mean Higher High Water (MHHW) tidal datum conversion inland beyond its original extent. VDatum was designed to vertically transform geospatial data among a variety of tidal, orthometric and ellipsoidal vertical datums - allowing users to convert their data from different horizontal/vertical references into a common system and enabling the fusion of diverse geospatial data in desired reference levels (https://vdatum.noaa.gov/). However, VDatum's conversion extent does not completely cover tidally-influenced areas along the coast. Because of the extent limitation and since most inundation mapping activities use a tidal datum as the reference zero (i.e., 1 meter of sea level rise on top of Mean Higher High Water), the NOAA Office for Coastal Management created this dataset for the purpose of extending the MHHW tidal datum beyond the areas covered by VDatum. The data do not replace VDatum, nor do they supersede the valid datum transformations VDatum provides. However, the data are based on VDatum's underlying transformation data and do provide an approximation of MHHW where VDatum does not provide one. In addition, the data are in a GIS-friendly format and represent MHHW in NAVD88, which is the vertical datum by which most topographic data are referenced. Data are in the UTM NAD83 projection. Horizontal resolution varies by VDatum region, but is either 50m or 100m. Data are vertically referenced to NAVD88 meters. More information about the NOAA VDatum transformation and associated tools can be found here.VDatum旨在实现多种潮汐、正高及椭球垂直基准间的地理空间数据垂直基准转换，支持用户将来自不同水平/垂直参考系的数据统一至同一参考系统，并可实现多源地理空间数据在所需参考高程层面的融合。本特定图层可实现从北美垂直基准面1988（NAVD 88）至平均高高潮（Mean Higher High Water, MHHW）的转换，单位为米。 该数据为美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）VDatum工具的衍生产品，将该工具的平均高高潮（MHHW）潮汐基准转换范围向内陆拓展至其原始覆盖边界之外。VDatum的设计初衷为实现多种潮汐、正高及椭球垂直基准间的地理空间数据垂直基准转换，支持用户将不同水平/垂直参考系的数据转换为统一系统，并可实现多源地理空间数据在所需参考高程层面的融合（相关信息可访问https://vdatum.noaa.gov/）。然而，VDatum的转换范围并未完全覆盖沿海潮汐影响区域。鉴于此范围限制，且多数淹没制图活动均以潮汐基准作为参考零点（例如，基于平均高高潮的海平面上升1米），NOAA海岸管理办公室创建了本数据集，旨在将MHHW潮汐基准的覆盖范围拓展至VDatum未覆盖的区域。本数据并非替代VDatum，也不会取代VDatum提供的有效基准转换结果。不过，本数据基于VDatum的底层转换数据，可在VDatum未提供转换结果的区域提供MHHW的近似值。此外，本数据采用兼容地理信息系统（GIS）的格式，以北美垂直基准面1988（NAVD 88）作为垂直参考系，而多数地形数据均以该基准为参照。数据采用通用横轴墨卡托（UTM）-北美大地基准面1983（NAD83）投影。水平分辨率随VDatum区域不同而有所差异，仅为50米或100米。数据的垂直参考系为NAVD 88米制单位。有关NOAA VDatum转换及相关工具的更多信息，请参见此处。