On 4/19/2012 9:13 AM, Gaffney, Sean P. wrote:
Hi all,
My name is Sean Gaffney, from the British Oceanographic Data Centre, and I'm
working on a project dealing with numerical model data that are in CF compliant
NetCDF, so I thought I'd sign up to the community.
The project I am working on aims to develop a web-based delivery system for
oceanographic numerical model data and has a module which allows visualisation
of the data. We've been using test CF data to fine-tune some of the technical
aspects of this visualisation.
I have a particular issue at the moment which I hope someone out there might be
able to assist me with.
My problem started when I found that the test CF data were passing the BADC CF
compliance checker, but not visualising properly. A check with the people who
developed the visualisation module led to the discovery that, while the CF
metadata were formatted correctly, the actual values within the metadata were
incorrect e.g. the valid_min and valid_max attributes for both the latitude and
longitude and dimensional variables had values which did not reflect the actual
range of data in the file. The visualisation was setting itself up based on the
values stored in the attributes and was therefore not displaying any data.
you should not use valid_min, valid_max, use actual_min, actual_max to
document the actual range of data. Unnecessarily using valid_min,
valid_max means that conforming software has to check each data value.
this hasnt made it into the docs yet, but you can see
https://cf-pcmdi.llnl.gov/trac/ticket/31
Has anyone in the CF community come across this sort of issue before and if so,
what solutions would you recommend? My initial thoughts were that I'd have to
develop some sort of code which interrogates the data file and compares the
entries in the CF metadata header against the actual data values in the file,
but I'd be interested to see what people think. Please bear in mind that I
won't actually be generating model runs myself, but will be receiving data from
people that have done so and need to know that I'm being given valid data and
metadata.
In my experience, one can have a valid CF file, but the metadata is
incorrect or insufficient to georeference data, since theres no
requirement in CF that data actually be georeferenced.
The CDM validator gives feedback on what data it can georeference
/visualize. Since we try to keep up with CF, its a good double check for
this problem, a complement to the CF validator(s).
http://motherlode.ucar.edu:8080/cdmvalidator/validate.html
However, it would not have caught your problem. For that, you would want
to visualize it and see that the picture was not what you would expect.
You could automate that process in an integration testing framework.
Sorry for making my first message to the CF community so long.
Looking forward to your responses
Yours
Sean Gaffney
BODC
--------------------------------------------------------------------------------
Sean Gaffney
Data Scientist
British Oceanographic Data Centre
Joseph Proudman Building
6 Brownlow Street
Liverpool
L3 5DA
UK
+44 (0)151 795 4950
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