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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 26/10/11 17:44, Tom Rink wrote: > Hi Martin, Peter Hi Tom, Sorry for the late answer, I had to do a little investing of my onw on this subject... >> - - Are the longitudes and latitudes values different from what a >> "vertical perspective" with right parameters would provide ? If they do, >> why ? If they don't, why not include a grid-mapping definition ? > > We've defined a netcdf structure for the GOES-R ABI (Advanced Baseline > Imager). > For navigation, similar to SEVIRI, the ABI defines a fixed grid (FGF) of > equal angle > spaced view angles from an nominal stationary point in space. The grid > can be represented > as a cross product of 2 one dimension arrays of the north-south, east-west > views angles in radians. The VerticalPerspective CF definition won't > work here > because it's a type of Map Projection which defines the transform x,y > (kilometers > for instance) <-> (Lon,Lat). Instead of two 1D arrays of view angles, a 2D > array of computed map projection plane values for the FGF views would > be required which defeats the purpose of defining the navigation > via a transform algorithm. We didn't want rewrite metadata > interpretation and > visualization components in the software, so we defined a > "grid_mapping_type" > for the ABI FGF whose "projection_x,y_coordinate" could be radians > instead of km. > Effectively a projection (radians, raidians) <-> (lon,lat). We did this > by extending, > actually some modification were required, classes distributed in the > ncIdv.jar. > See attached netcdf header file. Another nice advantage to the FGF is that > master lon/lat files don't change, and can be indexed directly if desired. The projection you describe here, based on viewing angles, is the one defined as "geos" in proj.4, and comes actually from Eumetsat's description for the meteosat satellites, see here: http://remotesensing.org/geotiff/proj_list/geos.html Maybe we could make a proposal to include this projection in the CF conventions ? In the satellite world, this would make a lot of sense. Best regards, Martin -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (GNU/Linux) Comment: Using GnuPG with Red Hat - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJOxL+zAAoJEBdvyODiyJI44EoH/1kk5aL87yiinij/lNJgxOED PTXkuD7DUsQT4rCEF5HcEJ2YSwwNMoGQxnghK8iSa/XWMzd3FbwevvDbgC9XFa+l 6Ek98ih5VrmbOMz6MuVRbQKg/A+s/cBBut6eJfEUjMowhjOpPR3YVVV/eCeQfT2k 39TTPTzNT2U6QuPYxvUNVz8jdWtSeWoBK8+BaHbXdPIVe09Rek+lgvDrpaqjjUGc bsHKiQynNvnMJ0YVODxY90UqNAlTbwn6rs2+KTQg/vl0Pozad17MCSO9ldbC+qeM KZAoYIhg97mVrtXIDSap4B30ZuJ5E1HB8w4gyezCUxoCCbTez2U4L2K9C0lfgXg= =fWiY -----END PGP SIGNATURE-----
begin:vcard fn:Martin Raspaud n:Raspaud;Martin org:SMHI adr;quoted-printable;quoted-printable:;;Folkborgsv=C3=A4gen 1;Norrk=C3=B6ping;;60176;Sweden email;internet:martin.raspaud@xxxxxxx tel;work:+46 (0)11 495 8261 tel;cell:+46 (0)11 495 8261 url:www.smhi.se version:2.1 end:vcard
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