VDatum SEP from Shapefile
This application computes a datum height (aka ellipsoid separation or SEP) grid. Input to the program consists of a Shapefile containing polygon(s) to delineate the areas of interest for the SEP output. A file of regular grid(s) with nodes spaced 100 meters x 100 meters is automatically created to cover the input polygon(s) and that file is fed into the VDatum software through its stock console interface. The resulting VDatum SEP grid file output is then passed through CARIS BASE Editor's batch processing interface to generate a CSAR SEP file.
Note that the HSD survey package from OPS may already include the ellipsoid-chart datum SEP CSAR
product(s) necessary for the assigned ERS project. User discretion advised. Contact HSTB, c/o Jack Riley for help.
The input Shapfile may be in any projection; the tool ultimately transforms the input spatial reference to Geographic NAD83 for output. Numerous input spatial references have been successfully tested, including U.S. State Plane with the associated possible non-metric units. The input data can also be un-projected [Geographic lat/lon] as well. If no spatial reference information is present in the Shapefile it prompts for an EPSG code to establish coordinates. Open your Shapefile in CARIS BASE Editor to verify the input horizontal datum, then consult/search EPSG Referencing for the needed code.
EPSG code examples: NAD83(2011) geographic = 6318, WGS84 geographic = 4326, World Mercator = 3395, WGS84 projected - UTM zone 18N = 32618, NAD83(2011) projected - UTM zone 18N = 6347, etc.
The corresponding VDatum uncertainty model for a given SEP calculation is equal to the root sum square (RSS) of the constituent transformations and source data therein (see Estimation of Vertical Uncertainties in VDatum link in Other Online Resources, below); e.g., here is an uncertainty calculation for NAD83-MLLW SEP in the Florida/Georgia - Shelf region:
NAD83 to NAVD88: 0.050 m NAVD88 source: 0.050 m NAVD88 to [L]MSL*: 0.041 m [L]MSL source*: 0.014 m [L]MSL to MLLW*: 0.043 m MLLW source*: 0.014 m ------------------------------------------------------------------ NAD83 to MLLW (RSS): 0.094 m (1 sigma); 0.185 m (95% = 1.96 sigma) * - Florida/Georgia - Shelf, Fort Lauderdale to Sapelo Island
Open the links below for detailed information.
Cached Version as packaged with Pydro Explorer (in case internet is not available):
VDatum SEP from Shapefile => CSAR Slideshow
Other Online Resources:
Estimation of Vertical Uncertainties in VDatum
HydroForum Document Library (SOPs etc)