The operation of the GEODAS software leads to the creation of data files in several formats. These files have a standardized file-naming scheme, but the files names and locations can be changed by the user. The standardized file name contains a file extension which identifies the format. Files resulting from a GEODAS Search and Data Retrieval are named as the Search KEY followed by the file extension, unless renamed differently by the user upon saving. For example, a data file in the ASCII HYD93 Exchange Format for a Search with key "anykey" would have a filename of "anykey.a93". User files created with GEODAS are saved in a subdirectory named key (e.g. subdirectory "anykey"), directly under the working directory. However, the user can choose to change both the name and location of the saved files. When data is saved as individual survey files, the filename is the NGDC Number followed by the file extension.
GEODAS application Hydro-Plot can read files in all these formats, even when created by other applications.
File extension depends on the format:
.mgn – Search Results file from a GEODAS Search (use to access Downloaded Search Data in Hydro-Plot)
.a77 – MGD77 ASCII Exchange Format
.a93 – HYD93 ASCII Exchange Format
.b93 – Binary HYD93 Format (format of data on Hydro CD/DVD)
.m93 – GEODAS M93 Binary XYZ Format (longitude,latitude,depth)
.xyz - ASCII or Binary XYZ (longitude,latitude,value)
.g98 or .g03 – GEODAS data Grid (Format GRD98)
.den – GEODAS data Grid (Format GRD98)
.rad – GEODAS data Grid (Format GRD98)
.asc – ArcVierw/ArcInfo ASCII Grid Format
MGD77 ASCII Exchange Format (*.a93):
This is the most common format used for exchange of deep ocean bathymetry, magnetics and gravity data. Standard MGD77 has a data record of 120 ASCII characters and is described in THE MARINE GEOPHYSICAL DATA EXCHANGE FORMAT - "MGD77". Note that if you downloaded the Truncated MGD77 version of the data records by selecting only some of the fields, you will not be able to view these files in Hydro-Plot.
GEODAS output filenames will contain file extension .a77 unless changed by the user.
HYD93 ASCII Exchange Format (*.a93):
HYD93 ASCII Format is the most common format used for exchange of hydrographic survey data. Standard HYD93 has a data record of 37 ASCII characters and is described in THE HYDROGRAPHIC SURVEYS DATA EXCHANGE FORMAT - "HYD93". in the main GEODAS Help System (see HYD93 Format). Note that if you downloaded the Truncated HYD93 version of the data records by selecting only some of the fields, you will not be able to view these files in Hydro-Plot.
GEODAS output filenames will contain file extension .a93 unless changed by the user.
Binary HYD93 CD/DVD Format:
HYD93 Binary Format is the format of the raw files on GEODAS NOS Hydrographic Surveys CD/DVD sets. The fields included in this version are binary representations of most of the fields in the HYD93 ASCII Exchange Format. The Binary HYD93 record structure follows:
LATITUDE X 1,000,000 4 Byte Integer degrees
LONGITUDE X 1,000,000 4 Byte Integer degrees
DEPTH VALUE X 10 4 Byte Integer meters, feet, fathoms
TYPE/CARTO CODE 2 Byte Integer type-code * 1000 + carto-code
type/carto code combines the type code field with the carto code field by multiplying the type code times 1000 and adding the carto code.
GEODAS output filenames will contain file extension .b93 unless changed by the user.
GEODAS M93 Binary XYZ Format (*.m93):
This format is a space-saving format which includes longitude, latitude and value (depths are negative, whole units). It is only used on a special set of SeaBeam derived multibeam data. The M93 Binary XYZ record structure follows:
LATITUDE X 1,000,000 4 Byte Integer degrees
LONGITUDE X 1,000,000 4 Byte Integer degrees
DEPTH VALUE 2 Byte Integer whole units
GEODAS filenames will contain file extension .m93 unless changed by the user.
ASCII or Binary XYZ Format (*.xyz):
X = longitude
Y = latitude
Z = data value
GEODAS can access a number of XYZ Formats. These include a standardized ASCII delimited xyz format, the GEODAS BINARY INTEGER XYZ FORMAT, Binary 8-byte Floating Point xyz format and Binary 8-byte Floating Point xyz format. All of these xyz formats can be used with the GEODAS Data Search and Retrieval and Hydro-Plot applications. Each data record contains fields for longitude, latitude, and value, as follows:
ASCII delimited XYZ Format: The records are ASCII. Each field is separated by a delimiter (space, comma or tab).Possible GEODAS Data Types in these XYZ Formats are:
corrected depth in meters
uncorrected depth in meters
magnetics total field in nanoteslas (gammas)
magnetics residual field in nanoteslas (gammas)
observed gravity in milligals
free air gravity in milligals
GEODAS output filenames will contain file extension .xyz unless changed by the user.
GEODAS Grid Format (*.g98, *.g03, *.den, *.rad):
GRD98 Grid Data Format is used on GEODAS CD/DVDs, and is output by GEODAS Grid Translator application. The format consists of a binary header which describes grid parameters, followed by the binary grid-cell values. In Hydro-Plot you can input data grids (.g98 or .g03) as well as density (.den) and Grid-Radius (.rad) grids. The format is described in THE GEODAS GRIDDED DATA FORMAT - GRD98
Note that GEODAS output depth values are in meters or tenths of meters.
GEODAS GRD98 gridded output filenames will contain file extension .g98 unless changed by the user.
ArcVierw/ArcInfo ASCII Grid Format (*.asc):
ArcVierw/ArcInfo ASCII Grid format can be output by GEODAS Grid Translator application, and can be input by GEODAS Hydro-Plot application, as well as GIS applications such as ArcView and ArcInfo (see ArcView Grids). The format consists of a header followed by the grid-cell values row by row.
The Header consists of 7 Parameter records, with a EOL (end-of-line) at the end of each record.
Each Parameter record consists of a keyword followed by the value (separated by a space).
XLLCORNER, YLLCORNER and CELLSIZE are in decimal degrees.
e.g.
NCOLS 229
NROWS 51
XLLCORNER -74.00000
YLLCORNER 45.33333
CELLSIZE 0.03333333
NODATA_VALUE 999999
The grid cells are arranged one row per record, with a EOL (end-of-line) at the end of each record. Cell values are integer or floating point values, separated by a space.
Note that GEODAS output depth values are in meters or tenths of meters.
ArcVierw/ArcInfo ASCII Grid output filenames will contain file extension .asc unless changed by the user.