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[UDUNITS #XIP-166037]: Need help migrating GrADS to udunits2


Actually, the UDUNITS-2 package supports the UDUNITS-1 API -- so you might not 
have to modify any code.

Otherwise, the following mappings should work:

    #include <udunits.h> -> #include <udunits2.h>

    utInit() -> ut_read_xml(NULL)

    utScan() -> ut_parse()

    utConvert(utUnit* from, utUnit* to, double* slope, double* intercept) ->
        cv_converter* converter = ut_get_converter(ut_unit* from, ut_unit* to);
        *intercept = cv_convert_double(converter, 0.0);
        *slope = cv_convert_double(converter, 1.0) - *intercept;

        Alternatively, instead of computing the slope and intercept, use the 
converter functions cv_convert_*() to convert the values and then call 
cv_free() on the converter.

utCalendar() is a bit more complicated because you have to know, a priori, that 
the encoding of the temporal offset is in seconds since 2001-01-01T00:00:00Z. I 
suggest you look at the utCalendar() function in the file "lib/udunits-2.c".

Please feel free to contact us further.

> GrADS uses just a few routines in the udunits library to parse the metadata 
> in a netcdf file:
> utInit() to initialize and load udunits.dat
> utScan() to convert a unit string into udunits format
> utCalendar() to convert a time unit string to integer values for yr, mo, dy, 
> hr, mn
> utConvert() to compare a parsed to a known/accepted unit string
> We have been statically linking our executables with udunits-1.11.7. I don’t 
> know how old this library is, but there’s been no need to upgrade because it 
> works perfectly and the interface in GrADS hasn’t changed in a very long time.
> It’s become a bit of a challenge to build the old library on newer operating 
> systems with newer compilers. The issue is further complicated because we are 
> moving to linking dynamically with all the dependent libraries. I would like 
> to use udunits2, since that seems to be what gets installed on unix systems 
> these days, and I want GrADS to be able to use a version of the library that 
> can be installed easily with yum or rpm. I have found RPM packages for 
> verison 2.2.20.
> I’d be very grateful if you could help me to migrate our use of the udunits 
> library to the new API syntax. Are there equivalents for the four routines we 
> currently use? If not, what would be the closest approximation?

Steve Emmerson

Ticket Details
Ticket ID: XIP-166037
Department: Support UDUNITS
Priority: Critical
Status: Closed
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