Thread: parsing units in FDSNStationXML

Started: 2013-04-10 19:22:53
Last activity: 2013-04-10 21:51:50
Topics: Web Services
Philip Crotwell
2013-04-10 19:22:53
Are there any guildlines for how the name of a unit in FDSNStationXML
should be formed? Other than "do it like SEED"?

I know the unit says it is the same as SEED blockette 34, but the SEED spec
says use SI but use all uppercase, which contradicts the SI convention that
case matters. So for example with prefixes m is milli and M is mega, and
for units g is gram while G is gauss and s is second while S is siemens. I
suppose most of seismology is covered by volt, meter, second and count, but
there are more and more types of data begin recorded at seismic stations
and so more varieties of units we need to support. And at some point it
would be nice to get away from a "formatted as FORTRAN-like equations with
all alphabetic characters in upper case" way of writing units and make us
of the existing standards for better portability and exchange within and
outside of seismology. It seems sad that the units are still just
unstructured strings that make it challenging for code to parse and
correctly interpret. Following something like this might be useful:
http://physics.nist.gov/cuu/Units/



Just a thought,
Philip

  • Philip Crotwell
    2013-04-10 21:51:50
    Follow up question, there are seemingly two types of "units" in
    FDSNStationXML, one used as an element and one as an attribute. The element
    one, UnitType, appears to say follow the SEED convention, so you have units
    with names like M/S, M and V. The unit attribute on FloatType is just a
    string with no documentation on how it is to be used, but looking at
    concrete uses of it in for example SecondType, VoltageType and
    DistanceType, it appears that the string should be things like SECONDS,
    VOLTS and METERS. So we have two different ways of specifying units in
    FDSNStationXML with different naming conventions.

    Perhaps even more confusing, the SampleRateType specifies the fixed unit
    string as SAMPLES/S, and which combines both unit naming conventions.

    Can you clarify the unit naming scheme? I would like to be able to parse
    the units, but it is much harder if there is not a clear mapping from unit
    to/from strings.

    Is this something that might be unified/simplified in a future version?

    Also, should
    Delay and Correction in DecimationType be SecondType?
    Amplitude in ResponseListElement and Numerator and Denominator in
    CoefficientsType be FloatNoUnitType as the units are in the enclosing
    element?
    NumeratorCoefficient be FloatNoUnitType (or FloatType) to be like
    CoefficientsType?


    thanks
    Philip


    On Wed, Apr 10, 2013 at 12:22 PM, Philip Crotwell <crotwell<at>seis.sc.edu>wrote:


    Are there any guildlines for how the name of a unit in FDSNStationXML
    should be formed? Other than "do it like SEED"?

    I know the unit says it is the same as SEED blockette 34, but the SEED
    spec says use SI but use all uppercase, which contradicts the SI convention
    that case matters. So for example with prefixes m is milli and M is mega,
    and for units g is gram while G is gauss and s is second while S is
    siemens. I suppose most of seismology is covered by volt, meter, second and
    count, but there are more and more types of data begin recorded at seismic
    stations and so more varieties of units we need to support. And at some
    point it would be nice to get away from a "formatted as FORTRAN-like
    equations with all alphabetic characters in upper case" way of writing
    units and make us of the existing standards for better portability and
    exchange within and outside of seismology. It seems sad that the units are
    still just unstructured strings that make it challenging for code to parse
    and correctly interpret. Following something like this might be useful:
    http://physics.nist.gov/cuu/Units/



    Just a thought,
    Philip


Page built 11:00:37 | v.6a0a3e16