|
|
|
The Polar HDF-EOS Data Imaging and Subsetting Tool (PHDIS) is a GUI tool that can read and visualize HDF-EOS grid data in the Lambert Azimuthal Equal Area projection and HDF-EOS swath data.
This tool requires
IDL
version 5.4 or higher. Under IDL, @make command will compile this program.
Under machines that are case-sensitive like UNIX, users may get errors during the
compilation. This is because make.pro specifies
file names in upper-case but actual file names are in lower-case. For example, make.pro
tries to compile NSIDC_DIST_GET_LATLON, but the actual file name is
nsidc_dist_get_latlon. Users need to either rename actual files or modify
make.pro.
We will briefly explain how to use this program to access a real HDF-EOS2 file. Since this package contains a few text documents, interested users can read them for detailed information.
Entering MAIN will execute the program and users will see a dialog box
that asks to input the name of the file to be displayed.
We selected an HDF-EOS2 file from the MYD29E1D product. You can get one file from here.
Then, PHDIS will read this file and show data fields in the file.
This file contains two grids: MOD_Grid_Seaice_4km_North and MOD_Grid_Seaice_4km_South. Each grid has two data fields starting with Sea_Ice_by_Reflectance and Ice_Surface_Temperature. We selected Ice_Surface_Temperature_NP from MOD_Grid_Seaice_4km_North.After selecting interested fields, PHDIS asks to input the value of stride as Figure 3 shows.
This value may need to be set properly if the size of the data field is big. If the value is too small for a big data array, huge computer resource may be consumed and the program may not proceed. As Figure 2 shows, we could proceed with the default value stride value 1 for our example. the size of the selected data field is 4501 * 4501.PHDIS read the selected data field, and draws a plot.
Using Image menu, users can adjust the palette and turn on/off coastlines and graticule. Also, a text,
-157.34948, -7.81093, in the left-top corner of window shows
the longitude value and the latitude value that correspond to the location
of the mouse cursor.
Users can also spawn a new window to see part of the plot with more details. Clicking and dragging the left button will set a region. Zoom To New Window menu in Region menu bar will create a new window that only shows the selected region.
Figure 5 shows a small part of the data field. You can see which region we selected from a small box at the right-bottom corner.Data Table menu in Region will show all values of the selected region in a table.
As Figure 6 shows, Some metadata information including geo-location information of the data field as well as data values of the selected region are displayed. If the user selects elements by clicking and dragging the left button, the region corresponding to the selected elements will be highlighted. For example, when 25 elements are selected as Figure 6 shows, users will see a small highlighted box that shows where 25 elements are mapped.
One may check other information from the tool web page
here .
