In order to geo-reference HDF data, the subfiles selected must have latitude values in the range -90 to 90 and longitude values in the range 0 to 360 or -180 to 180. If the latitude/longitude values have been scaled, or if they have an offset, they can be modified by double clicking on them to obtain a projection display:
HDF-EOS Swath Files
Swath files load just like any other self-describing data file. If there is appropriate geographic information in the file, a "GeoRef" button will appear in the Data Object. Caution: some HDF-EOS files have faulty geographic information and will not geo-reference properly. Note that subsetting must be done before geo-referencing the data.
HDF-EOS Point Files
Apart from the fact that these files are self-describing the method for ingesting their data is very similar to that for Table data. WebWinds will read these files and be able to create Images and Overlays from the data. Just as with ASCII tables the user can specify, through the use of schema, which columns of the data are to be read and of those, which are to be treated as dependent and independent variables. Point files can be classified into 2 general types. One type contains 'gridded' values for an independent variable (e.g. depth). We call this the 'Z Axis' and it can be specified as the following example shows:
The SubFile "Depth List" contains a list of standard depths. Since it only contains these depths, WebWinds notes that it has only one column and offers the possibility of using it as an independent variable by creating the "Z-Axis" button. Pressing this button adds this column as a 4th entry (3rd independent variable) in the Meta Data text field. With the Z axis chosen, the user can then choose a dependent variable from among the subfiles:
After selecting the "Temperature_Meas" SubFile, we note that we can choose from many columns. First we choose (i.e. click the appropriate entry in the "Columns" text area) the dependent variable, i.e. the temperature measurement itself (Column 12). Next we choose 2 independent variables, longitude and latitude. Note that these columns then appear in the "Schema". Before continuing, it is necessary to click the "Set Cols" button so that the selection will be recorded. Finally, clicking the "Load" button will load data into memory. These data can now be used as overlays, or displayed as an image.
A similar HDF-EOS Point file does not have a standard depth list:
Here, each set of measurements has its own set of depths. Therefore,
we choose "Parameter Value" (Column 15) as the dependent variable, and
longitude (3) latitude (2) and "Depth or Press" (13) as independent variables.