Jim et al,
Thanks and sorry for the long delay.
For what it is worth, yours is a fine generic example. David?s ?interval? comment seems to fit the bill. The question is then whether time_bounds is even necessary. It seems like up to the difference between (n) and (n-1), ?time_bounds? has a reasonable default, which is the space between ?time?.
Jim, the way you wrote it without ?interval? illustrates the work I have to do if the data are not marked as regularly, I would have to interrogate every single time cell to figure it out, and even then it isn?t clear if it is luck -- the next two hours could be different or a piece of missing data could add ambiguity. Perhaps more importantly for a metadata standard, it seems to be an omission of an important piece of information about the collection and processing program. To be honest this seems like something that should be in there even for instantaneous data.
Thanks so much to both of you,
Eli
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of David Hassell
Sent: Tuesday, July 24, 2018 8:46 AM
To: Jim Biard <jbiard at cicsnc.org>
Cc: CF Metadata <cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] metadata for regularly spaced data and averages
Hello Eli,
Would the standardised "interval" cell methods keyword be of use (
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html#recording-spacing-original-data<
https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fcfconventions.org%2FData%2Fcf-conventions%2Fcf-conventions-1.7%2Fcf-conventions.html%23recording-spacing-original-data&data=02%7C01%7C%7C94921b212562405e2f8608d5f17cab36%7Cb71d56524b834257afcd7fd177884564%7C0%7C0%7C636680440115696558&sdata=kyGARYHxVPwIN6ixZiBDA0RLfl2A2RnXgW3ouc6Kda0%3D&reserved=0>):
float data(time);
data:long_name = "The data";
data:cell_methods = "time: mean (interval: 1 hour)" ;
data:standard_name = "?????";
data:units = "????";
All the best,
David
On 23 July 2018 at 21:56, Jim Biard <jbiard at cicsnc.org<mailto:jbiard at cicsnc.org>> wrote:
Eli,
I'm not quite sure what you are looking for here. There are no other mechanisms in CF right now for describing sampling interval. Perhaps it would help if you described in greater detail the inputs to your process and the outputs from your process that you wish to store in a netCDF file. Here's what I am getting from what you wrote in your first message, with arbitrary numbers selected to make it concrete.
Inputs:
Each hour:
* Instrument takes 100 samples
* Instrument reports the time and the average of the 100 samples
Outputs for a netCDF file:
* One month of hourly average values
* The time each hourly average was reported
* The length of the acquisition interval
If this is what you have it is straightforward to store in netCDF using CF. Using CDL, the file structure would be:
netcdf file: sample.nc<
https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fsample.nc&data=02%7C01%7C%7C94921b212562405e2f8608d5f17cab36%7Cb71d56524b834257afcd7fd177884564%7C0%7C0%7C636680440115696558&sdata=xMOLOSOoq0xxjINQ0JW76ORPZCrQCZWeOhWpLCytit0%3D&reserved=0> {
dimensions:
time = 100;
bnds = 2;
variables:
float time(time);
time:long_name = "reporting time";
time:units = "seconds since 1970-01-01 00:00:00";
time:standard_name = "time";
time:axis = "T";
time:calendar = "gregorian";
time:bounds = "time_bounds";
float time_bounds(time, bnds);
float data(time);
data:long_name = "The data";
data:cell_methods = "time: mean (any comment that you find helpful)";
data:standard_name = "?????";
data:units = "????";
data:
time = 3600.0, 7200.0, ... ;
time_bounds = 0.0, 3600.0, 3600.0, 7200.0, 7200.0, 10800.0, ... ;
}
I hope this helps frame the question and/or provides a bit of the answer.
Grace and peace,
Jim
On 7/20/18 5:42 PM, Ateljevich, Eli at DWR wrote:
I have data that are recorded hourly after sampling the previous hour. The original sampling rate is high, but in some cases not provided so it doesn?t tend to make it into the metadata.
I can represent the hourly average with cell_methods and time_bnds, but it is painful for two reasons:
1. It costs some storage overhead in simple cases because the bounds are obvious.
2. The fact that it is regularly sampled is part of the station design. Here, I have to infer two things: (regular reporting interval and relative position of timestamp from time_bnds). The first one in particular is not a comment to me.
I can certainly see the lack of generality creeping looming, but this is such an important special case. Is there no common shorthand or possibly something I could at least do in *addition* to the cell_bounds. Am I missing a long conversation on this?
Obviously my question extends to any regular sampling geometries, I just picked a simple one in 1D.
Thanks,
Eli
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