| Project Name: | cdfj |
| Main developer(s): | Jane Exton and Simon Flower |
| Main user(s): | Jane Exton and Simon Flower |
| Computer language(s): | Java |
| Development environment: | Netbeans |
| Build Tool: | Maven |
| Source Control: | Git |
| BGS team: | Geomagnetism |
A pure Java library to read and write NASA CDF data files. The source code for the library is available from GITHub, here: https://github.com/autoplot/cdfj
Reader and writer for NASA CDF data files. Unlike previous libraries this is pure Java code and does not need any native shared libraries to work. The code has no external dependencies, either at compile or run time.
A few changes have to be made to the source code comments to prevent Javadoc errors from terminating the build process.
A change has been made to write "LeapSecondLastUpdated" metadata to CDF files.
Test code was written to investigate how the pure Java CDF library works, since no example code is provided with the library. The functions used in the test make use of all aspects of the CDF library needed for the BGS Intermagnet CDF library code
New code was introduced in gov.nasa.gsfc.spdf.cdfj.TimeUtil to access a local file that contains details of leap seconds. However this code could not be made to replicate the leap second behaviour of the CDF JNI library, and so has been left in as commented out code. The remaining paragraphs in this section refer to the new code this is commented out.
In the original source code the leap second data is embedded in the code, with a commented out section of code showing how to access the leap second table at https://hpiers.obspm.fr/eoppc/bul/bulc/UTC-TAI.history. The new code uses the embedded leap second table unless the environment variable or system property CDF_LEAPSECONDSTABLE is set, in which case the code attempts to load data from the file specified in the variable/property. The file is in the standard CDF format for leap seconds and can be obtained from here: https://cdf.gsfc.nasa.gov/html/CDFLeapSeconds.txt
A leap second file has been added to the library and is copied to the location specified by $CDF_LEAPSECONDSTABLE if the file does not already exist.
These instructions are untested.
The class gov.nasa.gsfc.spdf.cdfj.TimeUtil contains the leap second table. The boolean array "transition" is probably a list of leap seconds, where the first array dimension is the year (with the value 0 corresponding to 1970, 1 corresponding to 1971, ...) and the second array dimension indicating whether the leap second is applied in June (array subscript 0) or December (array subscript 1).
The array is initialized as:
boolean[][] transition = new boolean[100][2];
Allowing for leap seconds from 1970 to 2069. To add a new leap second, work out the first array dimension (year - 1970) and the second (June == 0, December == 1), then add an assignement for the relevant array element.
E.G. if a leap second is inserted in December 2026:
First array element = 2026 - 1970 = 56
Second array element for December = 1
New code:
transition [56] [1] = true;