Speciality files are those that may contain data of several types in an individual file. If CatchmentSIM recognises these files, it can simultaneously populate all relevant CatchmentSIM layers. This avoids the need to seperate processing in other GIS applications to strip individual data types into individual files.
An SRTM Water Body file is a polygon GIS file (usually a *shp file) that contains SRTM Water Body features including Lakes and Ocean polygons. Upon selection of a SRTM WB file, CatchmentSIM will automatically populate the Lakes and Ocean layers from the data within the SRTM WB file.
SRTM WB files can be downloaded for free from the following ftp site: ftp://e0srp01u.ecs.nasa.gov/srtm/version2/SWBD/
SRTM WB files have a specific file naming procedure with indicates the spatial extent of the data, that is:
| Note: | The <filename> identifies the southwest corner coordinates of the cell, represented as ‘HxxxVyyc’, where ‘Hxxx’ is the longitude, ‘Vyy’ is the latitude and ‘c’ denotes the continental delivery from the Jet Propulsion Laboratory with which the water body is associated. H is either ‘E’ or ‘W’ and ‘xxx’ takes on a value between 000 and 180. Similarly, V is either ‘N’ or ‘S’ and ‘yy” takes on a value between 00 and 90. The continental codes and the number of zipped files for each continental region are: a = Australia (888) e = Eurasia (5,388) f = Africa (1,809) i = Islands (141) n = North America (2,268) s = South America (1,735) |
Lakes
Lakes greater than a 600-meter minimum length and 183-meter minimum width requirement shall be depicted. Lake inlets (arms) shall be depicted until the inlet/arm reaches a width of 90m. Lakes will be sized by calculating the length of the medial axis; width will be calculated perpendicular to the medial axis. Lakes are portrayed at a single elevation value (in the underlying NASA SRTM DEM). Lake shoreline will be maintained such that it is at least one (1) meter higher than the lake elevation; containment will include maintaining this relationship with DTED posts diagonally adjacent to lakes.
Lake FACC code = BH080 (identifier in ShapeFile attributes).
Islands with a medial axis length greater than 300 meters shall be depicted. Smaller islands (down to14, 400m2) shall be depicted if 10 percent or more of the elevations of the island are greater than 15 meters above the surrounding water
Ocean
Ocean elevation shall be equal to 0 (in the underlying NASA SRTM DEM).
Feature and Attribute Coding Catalogue (FACC) code = BA040 (identifier in ShapeFile attributes)
Islands with a medial axis length greater than 300 meters shall be depicted. Smaller islands (down to14, 400 m2) shall be depicted if 10 percent or more of the elevations of the island are greater than 15 meters above the surrounding water.
Datums
The horizontal datum shall be the World Geodetic System 1984 (WGS84). The vertical datum shall be Mean Sea Level, as determined by the WGS84 Earth Gravitational Model 1996 (EGM 96) geoid.
This information has been copied from the SRTM Water Body Data Product Specific Guidance, the complete document can be found here:
ftp://e0srp01u.ecs.nasa.gov/srtm/version2/SWBD/SWBD_Documentation/
