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On 8/24/2010 1:07 AM, Martin Raspaud wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, At the danish and swedish meteorolical institutes, we have implemented the prototype suggestion. We have two points we would like to discuss here: - - Wavelength: we find it necessary to add the minimum and maximum wavelength (spectral range) to the metadata. We think it is not enough just to specify one wavelength for a band.
i think this is the same as a coordinate bounds, see section 7.1: http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html#cell-boundaries
- - Geolocalization: we have quite a lot of data that is easily represented on a grid, but the CF-convention requires the grid of lons and lats to be calculated. This is of course highly inconvenient for fixed grids (from a data storage and transfer perspective). We suggest adding a proj-string (proj.4 string definition) and an area-extent option in the convention for grids. To us, it makes a lot more sense than maintaining a list of accepted pre-defined grids in the convention.
1) there are a set of accepted projections in appendix F : http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html#appendix-grid-mappings does your data fall into one of those. if not, can you describe?proj-4 strings are an alternate representation, which have been discussed in the past on the CF list. you can include them, of course, but they are not currently part of the CF spec.
2) the question of having to include calculated lat/lons has also been discussed many times. I have advocated making these optional, but my opinion has not prevailed (yet). The Netcdf-Java software does not require them as long as a projection (grid_mapping) is specified. Other software may not know how to deal with the projections, so thats the argument for including.
Best regards, Martin Raspaud, Adam Dybbroe (SMHI) Esben Stigård Nielsen, Kristian Rune Larsen, Lars Ørum Rasmussen (DMI) Tom Whittaker skrev:We would like to suggest the following as a "starting point" that we can refine toward the goal of agreeing on a "basic" set of metadata and structure. It is an example of a multi-banded image structure that contains navigation on a point-by-point basis, and provides for linear calibration. The variable "names" are not critical, but the "standard_name" should be used by applications to identify the quantity. (In the following, most of the numbers are just samples....to make it more readable...) dimensions: x = 5304 ; y = 2438 ; band=16 variables: float lat(y, x); lat:standard_name = "latitude" ; lat:units = "degrees_north" ; lat:valid_range = -90.f, 90.f ; float lon(y, x) ; lon:standard_name = "longitude" ; lon:units = "degrees_east" ; lon:valid_range = -180.f, 180.f ; int band(band); double time; time:long_name = "Nominal time of image"; time:units="s since 1990-1-1 0:0:0"; string bandname(band); bandname:standard_name = "band_name" ; float offset(band) ; offset:standard_name="linear_calibration_offset"; float scale(band) ; scale:standard_name="linear_calibration_scale_factor"; float wavelength(band); wavelength:standard_name="radiation_wavelength"; wavelength:units="micron"; string units(band); units:standard_name="band_units"; short ImageData(band, y, x) ; ImageData:coordinates = "band lat lon" ; ImageData:valid_min = 1s ; ImageData:_FillValue = 0s ; ImageData:missing_value = 0s ; and for people who want/need to use a table look-up for calibration -- instead of the "linear_calibration..." variables, we would use: float lookup(band, 256); lookup:standard_name="calibration_lookup_table"; As Russ Rew pointed out, if there is only one band, it would be possible to dimension the Data as (y,x) but have the coordinates attribute contain "band". tom (with help from Tom Rink and Kaba Bah)-----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJMc2/IAAoJEBdvyODiyJI4w0wIAIw5QsZO9r3qmDnZLCz1ot7h +ws9qbrxklIfIxN7vuaSxTedonv++ulc9E90LVqyxKcOn/e8GM5XGSREjw8CAVhk 8PynsvvfHnjI5y3yZchoIy/znIt7bgTtGtTA6Ll+zgk3M5QxuFSC+jonfLk1EWzJ KFR6+Vtb64aztmBFYaKkvvOyUC0Xr/kVX7y+5K4sclHbQQaOSxO67yX1BdpWWPAX hXWWuLuLUZQNNwzi5o6FgQ2jom4mUxhZu/xbjeSl4fyehCgcw1TnE9BQ1aikTSaZ dIxTGI7gbHNARglIp2f7npaR6/yvCx5jQKf5SqgHQBSmyG2TTmzsxbokLACrsd8= =w/WO -----END PGP SIGNATURE----- _______________________________________________ cf-satellite mailing list cf-satellite@xxxxxxxxxxxxxxxx For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/
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