Hi Jim, (John,) et. al.,
The CF guide seems to be (unfortunately) vague on the subject of whether
missing values should be permitted in auxiliary coordinate variables.
As a starting position I think "no" is the correct answer -- missing
values should not be present in the coordinate system, itself. To do so
corrupts the integrity of the coordinate system.
Can you suggest a counter-example for satellite data? When the
coordinates become time-dependent (as in the case of satellite swaths)
and instrument failures occur, one could imagine situations where the
coordinates might indeed become missing. Though that seems like a
pathological example -- one where the dataset essentially has a void,
and there might be better ways to represent it.
- Steve
========================================================================
On 11/15/2010 6:28 AM, Jim Biard wrote:
Hi.
While reading the CF conventions regarding coordinate variables, I
found that coordinate variables are not supposed to have any "fill"
values. This makes sense to me. Does this same restriction hold for
a variable that is identified as an auxiliary coordinate via the
"coordinates" attribute on another variable? If both variables are
telemetry measurements, and thus subject to having missing values, can
one be validly used as an auxiliary coordinate variable, or should
this linkage not be made? The example pseudo-CDL below describes what
I am wondering about.
dimensions:
cycle = UNLIMITED;
variables:
double acq_time(cycle); // telemetry measurement
string start_time:units = "seconds since ...";
start_time:_FillValue = -999.3;
float baseplate_temperature(cycle); //also a telemetry measurement
string baseplate_temperature:units = "degrees C";
baseplate_temperature:_FillValue = -999.3;
string baseplate_temperature:coordinates = "acq_time";
Grace and peace,
Jim Biard
--
Jim Biard
Government Contractor, STG Inc.
Remote Sensing and Applications Division (RSAD)
National Climatic Data Center
151 Patton Ave.
Asheville, NC 28801-5001
jim.biard@xxxxxxxx
828-271-4330
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