For the various gridded datasets users can install the MS Windows
NGDC's GEODAS Desktop Software
to create and view custom grids off-line. Options include lat/lon subsetting, reformatting and changing cell size. Users can download the complete gridded datavbases in
ASCII and Binary formats from for ETOPO1 Global Relief Model, U.S. Coastal Relief Model and Great Lakes Bathymetry.
NGDC's Digital Elevation Model (DEM) Discovery Portal
provides links to these and many other gridded data sets.
GEODAS Grid Translator Design-a-Grid -
Custom grids from several GEODAS Gridded Databases can be created.
ETOPO1 Global Relief,
ETOPO2 Global Relief,
US Coastal Relief Model and
Great Lakes Bathymetry.
Users choose the criteria for their custom grid, including lat/lon area, grid cell size, format, etc.
The number of latitude and longitude cells of your grid will automatically be calculated and displayed.
After setting options click Submit button to create the grid.
Use option help icons for specific details about using the options. Use the Advanced Options button
for options such as Output Number-type, setting the Empty Grid Cell value, setting Grid Radius value,
creating only land or sea cells, etc. Resulting grid will have units of meters.
Grid Format Options -
Binary Raster Format: Arc-type header will be included.
can be viewed and edited in GEODAS Hydro-Plot. ArcGIS prefers Binary with Floating Pt numbers. ASCII Raster Format: Row by row series of space-delimited ASCII depths. Rows end with MS Windows-style End-of-Line.
An ASCII (Arc) Header will be attached to the beginning of the output file.
Format can be imported directly into ArcGIS, and can be viewed and edited in
GEODAS Hydro-Plot. XYZ (Delimited lon,lat,depth): Each grid value will be a separate record containing a lon, a lat
and a depth separated by spaces and terminated by a MS Windows-style End-of-Line.
An ASCII (Arc) Header is included in a separate file. Omit Empty Grid Cells:
For grid files of XYZ format you may include or omit the empty grid cell values.
Default is to omit these values, making it easier to import into various applications.
Lat/Lon Area Bounds - Choose the latitude/longitude boundaries of your Search area in decimal degrees or in degrees,
minutes and seconds. Switch between the 2 above methods with the button in the center of the lat/lon box.
Latitudes must be between 90 degrees North and 90 degrees South.
Longitude values must be between 180 degrees West and 180 degrees East (or -180 and +180).
Your area may not cross both 0 degrees and 180 degrees (e.g. 120E to 120E will not work).
If you wish your area to span the entire globe longitudinally, you should choose bounds of 180W to 180E (or -180 to +180),
or just click the World button. This has the effect of not using area as a Search criteria.
Use the Line or the Polygon(s) button to re-do your Search area as a (intersecting) line or as (multiple) polygons.
Grid Database - Source database of your custom grid:
1. ETOPO1 Global Gridded Relief
- Bathymetry and Elevation grids for the entire globe. Data is gridded at 1 minute.
2. ETOPO2 Global Gridded Relief
- Bathymetry and Elevation grids for the entire globe. Data is gridded at 2 minutes.
3. US Coastal Relief Model
- Bathymetric/Topographic grids at 3 arc-seconds for US coasts, created from the NOS Hydrographic
Surveys database. Some sets are available now; more are in progress.
4. Great Lakes Bathymetry
- Bathymetric/Topographic grids at 3 arc-seconds for the Great Lakes, created from the NOS Hydrographic
Surveys database. Custom grids can now be created for all of the Great Lakes.
Grid Lat/Lon Area Bounds -
Choose latitude/longitude bounds of your custom grid in degrees and
minutes. Latitudes must be between 90 deg North and 90 deg South.
Longitude values must be between 180 deg West and 180 deg East. Your grid may not cross both 0 deg and
180 deg. For grid to span the entire globe longitudinally (only relevent for ETOPO Global Relief databases),
choose bounds of 180W to 180E, or from 0E to 0E. Depending on Grid Database and
output Grid Cell Size, you may be restricted in your bounds. For example, if you have an output Grid Cell Size
of 2 minutes, you may not choose a lat/lon minutes value of an odd number (e.g. 3 minutes).
Initial values for a particular Grid Database are outer bounds of that database. Extending
bounds beyond that will result in the extra cells being filled with the Empty Grid Cell value (see
Grid Cell Value Parameters).
Grid Cell Size -
You may change the cell size of your custom grid from that of the source Grid Database.
However, your cell size must be a mulitple of the source database cell size. Only acceptable
cell sizes will be presented in the dialog. Be aware that cell size and area are related and certain
combinations will not work. For example, if you chose a lat/lon bounds minutes value of an odd number (e.g. 3 minutes),
you would not be able to have a cell size of 2 minutes. A warning will prompt you to change either lat/lon
boundaries or cell size.
Grid Land/Sea Coverage -
For US Coastal Relief Model only, Choose to transfer All Cells, Sea Cells Only,
or Land Cells Only from the source Coastal Relief Model database. Un-transferred
cells will contain the Empty Grid Cell Value.
Vertical Datum for Water Cells -
Allows using local Great Lakes vertical datums for non-land cells. When using the default Mean Sea Level,
water cells can have "depths" which are positive numbers. Using the
Local Lake Datums will create grids with the proper water depths, but the land cells will still be based on
acutal elevations (above mean sea level), thus showing a "cliff" where land starts.
Greenland/Antarctica Surface -
This allows the user to create grid based on the current surface of the ice sheet in Greenland and Antarctica, or to base the
grid on the bedrock (subtracting the ice thickness).
Grid Cell Parameters -
Number Type - Choose from 2-byte integers, 4-byte integers or 4-byte floating point (real) values.
Note that this is only used by the binary raster grid format. Empty Grid Cell Value - This is the value which will appear in the grid cells where there is no grid data from the
source Grid Database. This is not relevant to the ETOPO Global databases, since that databases have values for
all grid cells. Grid Radius Value - This is only relevant to US Coastal Relief Model grids. This option can be used to discard grid data depending
upon the proximity of the actual hydrographic data values. i.e. NGDC has used NOS Hydrographic Survey Data to create
grid data values for the grid cells in each grid. Use a value of -1 if you do not wish the Grid Radius algorithm
to be applied. But if you do not wish to use grid values where actual data was not
in close proximity, you may apply the Grid Radius algorithm. If Grid Radius is set to zero or greater and the nearest
actual data was more than Grid Radius grid cells away, the output cell will be given the Empty Grid Cell Value instead
of the value contained in the Coastal Relief Model grid files. Note that Grid-Radius values are based on the Coastal
Relief Model grid cell size (3 arc-seconds), not the output cell size.