Hi Mark,
We are using the ancilliary_variables attribute in a real world case for CTD
profile data
(1 netCDF per CTD profile). Not sure if our use case fits with with your
examples a,b,c but here is a abbreviated CDL version:-
dimensions:
pressure = UNLIMITED ; // (9 currently)
variables:
double time ;
time:standard_name = "time" ;
....
byte time_qc_flag;
time_qc_flag:long_name = "quality control flag for time (Level 1 flag)" ;
....
double latitude ;
latitude:standard_name = "latitude" ;
...
double longitude ;
longitude:standard_name = "longitude" ;
...
byte position_qc_flag;
position_qc_flag:long_name = "quality control flag for position (Level 1
flag)" ;
....
double pressure(pressure) ;
pressure:standard_name = "sea_water_pressure" ;
...
double temperature(pressure) ;
temperature:_FillValue = -99.99 ;
temperature:standard_name = "sea_water_temperature" ;
temperature:units = "degrees_C" ;
temperature:valid_min = -2 ;
temperature:valid_max = 40 ;
temperature:ancillary_variables = "temperature_whole_profile_flag
temperature_qc_flag temperature_sd_test" ;
temperature:coordinates = "time latitude longitude pressure" ;
byte temperature_whole_profile_flag ;
temperature_whole_profile_flag:long_name = "qc flag for whole temperature
profile (primary L1 flag)" ;
temperature_whole_profile_flag:quality_control_convention = "Proposed IODE qc
scheme March 2012" ;
temperature_whole_profile_flag:valid_min = 1 ;
temperature_whole_profile_flag:valid_max = 9 ;
temperature_whole_profile_flag:flag_values = 1b, 2b, 3b, 4b, 9b ;
temperature_whole_profile_flag:flag_meanings = "good not_evaluated_or_unknown
suspect bad missing" ;
byte temperature_qc_flag(pressure) ;
temperature_qc_flag:long_name = "quality control flag for temperature (primary
Level 1 flag)" ;
temperature_qc_flag:standard_name = "sea_water_temperature status_flag" ;
temperature_qc_flag:quality_control_convention = "Proposed IODE qc scheme
March 2012" ;
temperature_qc_flag:valid_min = 1 ;
temperature_qc_flag:valid_max = 9 ;
temperature_qc_flag:flag_values = 1b, 2b, 3b, 4b, 9b ;
temperature_qc_flag:flag_meanings = "good not_evaluated_or_unknown suspect bad
missing" ;
temperature_qc_flag:coordinates = "time latitude longitude pressure" ;
byte temperature_sd_test(pressure) ;
temperature_sd_test:long_name = "qc flag for monthly temperature standard
deviation test (secondary L2 flag)"
temperature_sd_test:quality_control_convention = "Proposed IODE qc scheme
March 2012" ;
temperature_sd_test:valid_min = 0 ;
temperature_sd_test:valid_max = 2 ;
temperature_sd_test:flag_values = 0b, 1b, 2b ;
temperature_sd_test:flag_meanings = "passed failed unknown" ;
temperature_sd_test:coordinates = "time latitude longitude pressure" ;
double salinity(pressure) ;
salinity:_FillValue = -99.99 ;
salinity:standard_name = "sea_water_practical_salinity" ;
salinity:units = "psu" ;
salinity:valid_min = 0 ;
salinity:valid_max = 45 ;
salinity:ancillary_variables = "salinity_whole_profile_flag salinity_qc_flag
salinity_sd_test"
salinity:coordinates = "time latitude longitude pressure" ;
byte salinity_whole_profile_flag ;
salinity_whole_profile_flag:long_name = "qc flag for whole salinity profile
(primary L1 flag)" ;
salinity_whole_profile_flag:quality_control_convention = "Proposed IODE qc
scheme March 2012" ;
salinity_whole_profile_flag:valid_min = 1 ;
salinity_whole_profile_flag:valid_max = 9 ;
salinity_whole_profile_flag:flag_values = 1b, 2b, 3b, 4b, 9b ;
salinity_whole_profile_flag:flag_meanings = "good not_evaluated_or_unknown
suspect bad missing" ;
byte salinity_qc_flag(pressure) ;
salinity_qc_flag:long_name = "quality control flag for salinity (primary Level
1 flag)" ;
salinity_qc_flag:standard_name = "sea_water_practical_salinity status_flag" ;
salinity_qc_flag:quality_control_convention = "Proposed IODE qc scheme March
2012" ;
salinity_qc_flag:valid_min = 1 ;
salinity_qc_flag:valid_max = 9 ;
salinity_qc_flag:flag_values = 1b, 2b, 3b, 4b, 9b ;
salinity_qc_flag:flag_meanings = "good not_evaluated_or_unknown suspect bad
missing" ;
salinity_qc_flag:coordinates = "time latitude longitude pressure" ;
byte salinity_sd_test(pressure) ;
salinity_sd_test:long_name = "qc flag for monthly salinity standard deviation
test (secondary L2 flag)"
salinity_sd_test:quality_control_convention = "Proposed IODE qc scheme March
2012" ;
salinity_sd_test:valid_min = 0 ;
salinity_sd_test:valid_max = 2 ;
salinity_sd_test:flag_values = 0b, 1b, 2b ;
salinity_sd_test:flag_meanings = "passed failed unknown" ;
salinity_sd_test:coordinates = "time latitude longitude pressure" ;
int profile ; //Unique integer to identify each profile
profile:long_name = "profile identifier"
....
Andrew Walsh
----- Original Message -----
From: "Hedley, Mark" <mark.hed...@metoffice.gov.uk>
To: <ngalbra...@whoi.edu>; <cf-metadata@cgd.ucar.edu>
Sent: Thursday, February 14, 2013 10:40 PM
Subject: Re: [CF-metadata] Ancillary Data
Hi Nan
I think I understand you approach, it seems logical and helpful to me.
It feels like all your examples are in my category b:
b. reference a subset of the file dimensions referenced by the data variable
with the ancillary_variables attribute
and thus relate to the data variable in the same way auxiliary_coordinates do,
just with different inferred semantics.
many thanks for the feedback
mark
-----Original Message-----
From: CF-metadata on behalf of Nan Galbraith
Sent: Wed 13/02/2013 19:55
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] Ancillary Data
I use a singleton variable to record the magnetic correction that's been
applied to my wind and/or current variables; it's dim(1) and is listed as
an ancillary to any variables that have been affected by the rotation.
It could be an attribute of each of those variables, but making it a
free-standing
variable lets me give it units and attributes. That's important because I
record the model name and version date, the URL of the NGDC calculator
site,
the inputs to the model (date and location for which the calculation was
done)
and the estimated rate of change.
Maybe this is just a technicality - but I also use an empty 'container'
variable for
instruments, which has ancillary variables with a depth dimension for
manufacturer,
model, serial number, and reference URL. The instrument variable is
tied to 'obs data'
variables via NODC's 'instrument' attribute, but has no dimensions of
its own; the
individual component variables (like serial number) have a dimension
that matches
the depth dimension of the obs data variables.
- Nan
On 2/13/13 12:15 PM, Hedley, Mark wrote:
Hello CF community
I have been perusing the CF conventions again, particularly the section on
Ancillary Data
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/ch03s04.html
The conventions make the statement:
The nature of the relationship between variables associated via
ancillary_variables must be determined by other attributes.
The example given provides data variables which reference the same dimensions
in the file: thus they data arrays are the same size. However, the
conventions do not seem to mandate this.
I am interested in the use of the
ancillary_variables
attribute in real world datasets.
Do people have examples they can share of ancillary datasets which:
a. reference the same file dimensions as the data variable with the
ancillary_variables attribute references
b. reference a subset of the file dimensions referenced by the data
variable with the ancillary_variables attribute
c. reference file dimensions which are not referenced by the data variable
with the ancillary_variables attribute
I am particularly interested in examples of case c, as I feel this is
markedly different from cases a and b and requires a different kind of
support if it is in use.
many thanks
mark
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--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
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