Folks: RE: “ Definition: "x" indicates a vector component along the grid x-axis, when this is not true longitude, positive with increasing x. Angular projection coordinates are angular distances in the x- and y-directions on a plane onto which the surface of the Earth has been projected according to a map projection. The relationship between the angular projection coordinates and latitude and longitude is described by the grid_mapping.”
specifically, "are angular distances in the x- and y-directions on a plane onto which the surface of the Earth has been projected” In the case of both the GOES-R and EUMETSAT, the angular distances are projected onto an Earth ellipsoid, whose definition is captured in the grid mapping. v/r randy > On Apr 19, 2018, at 10:06 AM, Daniel Lee <daniel....@eumetsat.int> wrote: > > Hi Jim, > > I for one find this more confusing than Ethan's definition, but maybe it's > because I'm too far gone in my discipline to see the scope for > misunderstanding. > > That being said, if we're being that general my feeling says to me that we > may risk converging on a standard which isn't really applicable to any more > specific application. Currently there is a proposal for CF-2 devoted > specifically to swath data > <https://github.com/Unidata/EC-netCDF-CF/blob/master/swath/swath.adoc>, and > this has the potential to cover the need for a specific geostationary > projection as well. Maybe that would also be a good path to take for other > coordinate systems with non-linear relationships between projection > coordinates and coordinates of other CRS - kind of general, but not overly > abstract. > > Cheers, > Daniel > > From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu > <mailto:cf-metadata-boun...@cgd.ucar.edu>] On Behalf Of Jim Biard > Sent: 19 April 2018 15:32 > To: cf-metadata@cgd.ucar.edu <mailto:cf-metadata@cgd.ucar.edu> > Subject: Re: [CF-metadata] Fix Geostationary projection, including proposal > for two new standard names > > Hi. > > Here's a couple of thoughts. > > The definition that Ethan has proposed fails to note that the angles are with > respect to a normal to the projection surface at a point along the normal. I > guess the phrase "angular distance" implies this, but my first read had me > feeling confused about what was being described. On checking, I see that this > is a minimalist variation on the projection_x/y_coordinate definitions. Do > folks think that this is clear enough as is? > > I know we tend not to follow this course, but I am wondering if we might not > be better served overall by taking a more generic approach and defining > parametric coordinates u and v (projection_u_coordinate and > projection_v_coordinate). The canonical units would be '1' (unitless). The > definition for parametric_u_coordinate would be something like > > "u" indicates an independent variable, or parameter, associated with an axis > of a coordinate grid where this parameter is not a linear distance in a > projection coordinate system, a Cartesian coordinate element, or a geographic > latitude or longitude. The geographic latitude and longitude of each point in > the coordinate grid are functions of the parameters associated with the grid > axes. The relationship between the parametric coordinates and latitude and > longitude is described by the grid_mapping. > > The geostationary projection is one use case covered by parametric > coordinates, and there are others. The native coordinates for most all > satellite swath data are parametric - mirror angle and time, for example. > > Grace and peace, > > Jim > > On 4/19/18 5:06 AM, Daniel Lee wrote: > Hi Ethan, > > At first blush this looks pretty good. If we can agree on this in a short-ish > time frame, it might be possible for EUMETSAT to publish data exclusively > using these standard names - the planned launch date for MTG I1 is late 2021. > This sounds like it's very far away, but in the space sector our planning > horizons are a lot longer, so there's already a lot of work being done on it > right now and at some point in the near future the specs will freeze. > > Best regards, > Daniel > > From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu > <mailto:cf-metadata-boun...@cgd.ucar.edu>] On Behalf Of Ethan Davis > Sent: 19 April 2018 05:40 > To: CF metadata <cf-metadata@cgd.ucar.edu> <mailto:cf-metadata@cgd.ucar.edu> > Subject: [CF-metadata] Fix Geostationary projection, including proposal for > two new standard names > > Hi all, > > Here's an initial proposal for fixing the geostationary projection as we've > been discussing. > > Two new standard names: > > Name: projection_x_angular_coordinate > Canonical units: radian > Definition: "x" indicates a vector component along the grid x-axis, when this > is not true longitude, positive with increasing x. Angular projection > coordinates are angular distances in the x- and y-directions on a plane onto > which the surface of the Earth has been projected according to a map > projection. The relationship between the angular projection coordinates and > latitude and longitude is described by the grid_mapping. > > Name: projection_y_angular_coordinate > Canonical units: radian > Definition: "y" indicates a vector component along the grid y-axis, when this > is not true latitude, positive with increasing y. Angular projection > coordinates are angular distances in the x- and y-directions on a plane onto > which the surface of the Earth has been projected according to a map > projection. The relationship between the angular projection coordinates and > latitude and longitude is described by the grid_mapping. > > Replace the text of the current "Map coordinates:" section with > > The x (abscissa) and y (ordinate) projection coordinates are identified by > the `standard_name` attribute values `projection_x_angular_coordinate` and > `projection_y_angular_coordinate` respectively. In the case of this > projection, the projection coordinates are directly related to the scanning > angle of the satellite instrument. > > Add a deprecation note below the current "Notes:" > > Deprecation Note: > The use of `projection_x_coordinate` and `projection_y_coordinate` for this > projection has been deprecated. > > The initial definition of this projection used these standard names to > identify the projection coordinates even though their canonical units > (meters) do not mach those required for this projection (radians). > > Perhaps we should include information on when the deprecated feature was in > effect: > > The initial definition for this projection was agreed on in May 2012 though > it was not in the CF document until 1.7 was released in Sept 2017. It was > corrected in ??? 2018. > > And do we also want to include information about large datasets that use this > deprecated technique: > > In that time, several satellite missions were developed and launched that > generate data that use this now deprecated method including GOES-R > (operational in Dec 2017), EUMETSAT ???? ... > > That could alert people to the likelihood they (or any software they develop) > might run into data using this deprecated feature. > > I'll move this to a Trac ticket (with an accompanying GitHub PR) once we > discuss a bit. > > Cheers, > > Ethan > > Any email message from EUMETSAT is sent in good faith but shall neither be > binding nor construed as constituting a commitment by EUMETSAT, except where > provided for in a written agreement or contract or if explicitly stated in > the email. Please note that any views or opinions presented in this email are > solely those of the sender and do not necessarily represent those of > EUMETSAT. This message and any attachments are intended for the sole use of > the addressee(s) and may contain confidential and privileged information. Any > unauthorised use, disclosure, dissemination or distribution (in whole or in > part) of its contents is not permitted. If you received this message in > error, please notify the sender and delete it from your system. > > > > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu <mailto:CF-metadata@cgd.ucar.edu> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > <http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> > > -- > <~WRD000.jpg> <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 > e: jbi...@cicsnc.org <mailto:jbi...@cicsnc.org> > o: +1 828 271 4900 > > Connect with us on Facebook forclimate > <https://www.facebook.com/NOAANCEIclimate> and ocean and geophysics > <https://www.facebook.com/NOAANCEIoceangeo>information, and follow us on > Twitter at@NOAANCEIclimate <https://twitter.com/NOAANCEIclimate> > and@NOAANCEIocngeo <https://twitter.com/NOAANCEIocngeo>. > > > Any email message from EUMETSAT is sent in good faith but shall neither be > binding nor construed as constituting a commitment by EUMETSAT, except where > provided for in a written agreement or contract or if explicitly stated in > the email. Please note that any views or opinions presented in this email are > solely those of the sender and do not necessarily represent those of > EUMETSAT. This message and any attachments are intended for the sole use of > the addressee(s) and may contain confidential and privileged information. Any > unauthorised use, disclosure, dissemination or distribution (in whole or in > part) of its contents is not permitted. If you received this message in > error, please notify the sender and delete it from your system. > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu <mailto:CF-metadata@cgd.ucar.edu> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > <http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> _____________________________________ Randy C Horne (rho...@excaliburlabs.com) Principal Engineer, Excalibur Laboratories Inc. voice & fax: (321) 952.5100 cell: (321) 693.1074 url: http://www.excaliburlabs.com
_______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
