[CF-metadata] Best practice to include spatial resolution for projected data

[Mary Jo Brodzik]

I am producing a gridded data set using CF-1.6 conventions. In a given
file, the data are projected onto one of three possible projections:
Northern or Southern Lambert Azimuthal Equal Area (LAEA), or Cylindrical
Equal-Area (CEA). With each data variable in the file, I do include the
grid_mapping attribute and I am populating my grid_mapping variable with
the required projection information as listed here:

http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html

Also in a given file, the spatial resolution will be one of 25, 12.5, 6.25
or 3.125 km, and although this is obvious from the x and y dimension
variable values, I am looking for a place to include the spatial
resolution for a human who is reading the metadata.

I assume an attribute in the grid_mapping variable would be the place for
this. At first I thought it was one of the "scale_factor*" attributes,
e.g. "scale_factor_at_projection_origin", but for CEA, this would be a
misnomer, since the value is the scale at true latitude, not the
projection origin at all. Also, the convention says to include "either
standard_parallel or scale_factor_at_projection_origin", so now I'm
beginning to think these "scale_factor_*" attributes are not the correct
place at all for this information.

I see in the NCEI template file for gridded data

https://www.nodc.noaa.gov/data/formats/netcdf/v2.0/grid.cdl

that they recommend global attributes like "geospatial_lat_resolution" and
"geospatial_lon_resolution", with a string value of "0.1 degree" or "100
meters" which is almost what I am looking for, but of course since I have
projected data it would not be "lat" or "lon".

Can anyone recommend a best practice for my projected data case that I
can follow?

Thank you,
Mary Jo Brodzik

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Mary Jo Brodzik, Senior Associate Scientist, 303-492-8263
NSIDC/CIRES, Univ. of Colo. at Boulder, 449 UCB, Boulder, CO 80309-0449
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Jim Biard]

Mary Jo,

It's a problem that doesn't currently have an official solution. The
geospatial_lat/lon_resolution are from the ESIP Attribute Convention for
Dataset Discovery (ACDD) <http://wiki.esipfed.org/index.php/ACDD>, but
they haven't thought through to a generalization yet. You could make
your own attributes geospatial_resolution or geospatial_x_resolution and
geospatial_y_resolution, or you could think of longitude as being ~x and
latitude as ~y and use the existing attributes. You can also query the
ESIP people and request that they add a new set of attributes that would
handle this. I think the CF community likely considers this to be more
of an ACDD issue.

Grace and peace,

Jim

Post by Mary Jo Brodzik
I am producing a gridded data set using CF-1.6 conventions. In a
given file, the data are projected onto one of three possible
projections: Northern or Southern Lambert Azimuthal Equal Area (LAEA),
or Cylindrical Equal-Area (CEA). With each data variable in the file,
I do include the grid_mapping attribute and I am populating my
grid_mapping variable with the required projection information as
http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html
Also in a given file, the spatial resolution will be one of 25, 12.5,
6.25 or 3.125 km, and although this is obvious from the x and y
dimension variable values, I am looking for a place to include the
spatial resolution for a human who is reading the metadata.
I assume an attribute in the grid_mapping variable would be the place
for this. At first I thought it was one of the "scale_factor*"
attributes, e.g. "scale_factor_at_projection_origin", but for CEA,
this would be a misnomer, since the value is the scale at true
latitude, not the projection origin at all. Also, the convention says
to include "either standard_parallel or
scale_factor_at_projection_origin", so now I'm beginning to think
these "scale_factor_*" attributes are not the correct place at all for
this information.
I see in the NCEI template file for gridded data
https://www.nodc.noaa.gov/data/formats/netcdf/v2.0/grid.cdl
that they recommend global attributes like "geospatial_lat_resolution"
and "geospatial_lon_resolution", with a string value of "0.1 degree"
or "100 meters" which is almost what I am looking for, but of course
since I have projected data it would not be "lat" or "lon".
Can anyone recommend a best practice for my projected data case that I
can follow?
Thank you,
Mary Jo Brodzik
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Mary Jo Brodzik, Senior Associate Scientist, 303-492-8263
NSIDC/CIRES, Univ. of Colo. at Boulder, 449 UCB, Boulder, CO 80309-0449
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_______________________________________________
CF-metadata mailing list
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata

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*Research Scholar*
Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/>
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NOAA National Centers for Environmental Information <http://ncdc.noaa.gov/>
/formerly NOAA’s National Climatic Data Center/
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[Mary Jo Brodzik]

Thanks, Jim, I will take it to ACDD.

Mary Jo

Date: Tue, 16 Aug 2016 12:43:57 -0400
Subject: Re: [CF-metadata] Best practice to include spatial resolution for
projected data
Mary Jo,
It's a problem that doesn't currently have an official solution. The
geospatial_lat/lon_resolution are from the ESIP Attribute Convention for
Dataset Discovery (ACDD) <http://wiki.esipfed.org/index.php/ACDD>, but they
haven't thought through to a generalization yet. You could make your own
attributes geospatial_resolution or geospatial_x_resolution and
geospatial_y_resolution, or you could think of longitude as being ~x and
latitude as ~y and use the existing attributes. You can also query the ESIP
people and request that they add a new set of attributes that would handle
this. I think the CF community likely considers this to be more of an ACDD
issue.
Grace and peace,
Jim

Post by Mary Jo Brodzik
I am producing a gridded data set using CF-1.6 conventions. In a given
Northern or Southern Lambert Azimuthal Equal Area (LAEA), or Cylindrical
Equal-Area (CEA). With each data variable in the file, I do include the
grid_mapping attribute and I am populating my grid_mapping variable with
http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html
Also in a given file, the spatial resolution will be one of 25, 12.5, 6.25
or 3.125 km, and although this is obvious from the x and y dimension
variable values, I am looking for a place to include the spatial resolution
for a human who is reading the metadata.
I assume an attribute in the grid_mapping variable would be the place for
this. At first I thought it was one of the "scale_factor*" attributes,
e.g. "scale_factor_at_projection_origin", but for CEA, this would be a
misnomer, since the value is the scale at true latitude, not the projection
origin at all. Also, the convention says to include "either
standard_parallel or scale_factor_at_projection_origin", so now I'm
beginning to think these "scale_factor_*" attributes are not the correct
place at all for this information.
I see in the NCEI template file for gridded data
https://www.nodc.noaa.gov/data/formats/netcdf/v2.0/grid.cdl
that they recommend global attributes like "geospatial_lat_resolution" and
"geospatial_lon_resolution", with a string value of "0.1 degree" or "100
meters" which is almost what I am looking for, but of course since I have
projected data it would not be "lat" or "lon".
Can anyone recommend a best practice for my projected data case that I can
follow?
Thank you,
Mary Jo Brodzik
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Mary Jo Brodzik, Senior Associate Scientist, 303-492-8263
NSIDC/CIRES, Univ. of Colo. at Boulder, 449 UCB, Boulder, CO 80309-0449
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_______________________________________________
CF-metadata mailing list
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata

--
CICS-NC <http://www.cicsnc.org/> Visit us on
Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
*Research Scholar*
Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/>
North Carolina State University <http://ncsu.edu/>
NOAA National Centers for Environmental Information <http://ncdc.noaa.gov/>
/formerly NOAA¢s National Climatic Data Center/
151 Patton Ave, Asheville, NC 28801
o: [phone]
/Connect with us on Facebook for climate
<https://www.facebook.com/NOAANCEIclimate> and ocean and geophysics
<https://www.facebook.com/NOAANCEIoceangeo> information, and follow us on
@NOAANCEIocngeo <https://twitter.com/NOAANCEIocngeo>. /

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Mary Jo Brodzik, Senior Associate Scientist, 303-492-8263
NSIDC/CIRES, Univ. of Colo. at Boulder, 449 UCB, Boulder, CO 80309-0449
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Seth McGinnis]

You are correct that the scale_factor_* attributes are not the right
place for this information. The grid_mapping variable is a container
for the parameters that describe the projected coordinate system, but
they don't actually depend on the resolution of the grid, just the
Cartesian coordinates attached to the grid.

I am not aware of any established best practices in the world of
regional climate modeling; the spatial resolution generally gets lumped
in with the definition of the domain.

Given that lacuna, I think the best practice would be to extend the
closest existing recommendation according to the principle of least
surprise. In this case, I would follow the NCEI's suggestion of using
global attributes and simply drop the _lat_ component. I.e.:

// global attributes:
:geospatial_resolution = "12.5 km" ;

(Or, if they're different, change it to geospatial_x_resolution &
geospatial_y_resolution.)

In other words, what Jim said. He just got to the "send" button before
me. :)

Cheers,

--Seth

----
Seth McGinnis
Associate Scientist IV
NARCCAP Data Manager
IMAGe / CISL / NCAR
-----

Post by Mary Jo Brodzik
I am producing a gridded data set using CF-1.6 conventions. In a given
Northern or Southern Lambert Azimuthal Equal Area (LAEA), or Cylindrical
Equal-Area (CEA). With each data variable in the file, I do include the
grid_mapping attribute and I am populating my grid_mapping variable with
http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html
Also in a given file, the spatial resolution will be one of 25, 12.5,
6.25 or 3.125 km, and although this is obvious from the x and y
dimension variable values, I am looking for a place to include the
spatial resolution for a human who is reading the metadata.
I assume an attribute in the grid_mapping variable would be the place
for this. At first I thought it was one of the "scale_factor*"
attributes, e.g. "scale_factor_at_projection_origin", but for CEA, this
would be a misnomer, since the value is the scale at true latitude, not
the projection origin at all. Also, the convention says to include
"either standard_parallel or scale_factor_at_projection_origin", so now
I'm beginning to think these "scale_factor_*" attributes are not the
correct place at all for this information.
I see in the NCEI template file for gridded data
https://www.nodc.noaa.gov/data/formats/netcdf/v2.0/grid.cdl
that they recommend global attributes like "geospatial_lat_resolution"
and "geospatial_lon_resolution", with a string value of "0.1 degree" or
"100 meters" which is almost what I am looking for, but of course since
I have projected data it would not be "lat" or "lon".
Can anyone recommend a best practice for my projected data case that I
can follow?
Thank you,
Mary Jo Brodzik
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Mary Jo Brodzik, Senior Associate Scientist, 303-492-8263
NSIDC/CIRES, Univ. of Colo. at Boulder, 449 UCB, Boulder, CO 80309-0449
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_______________________________________________
CF-metadata mailing list
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata