Aleksandar, My comment was (supposed to be) that the definition for platform_orientation was weak. I apologize for not being clear.
I see from the diagram (thank you) that your term is nothing like platform_orientation; with your zenith angle reference, all becomes clear. I would like to suggest minor modifications to save others from my mistakes. In this usage, the platform is *not* the vehicle from which this particular observation is made -- the platform is the thing being observed. (It may also make observations, but they aren't relevant to this parameter, that I can tell.) So could we drop the first sentence, and explicitly say something like "Platform_azimuth_angle is the angle whose vertex is at the observation point. It is the horizontal angle between..."? For those who know about solar_azimuth_angle I'm sure this is unnecessary, but obviously a few of us got lost. (Note the definition did not say the "observation point" was at the vertex, and I totally misread the definition -- as I suspect Bruno did -- in the other direction, with the observation point at a distance from the platform. My extensive exposure to platform-based coordinate systems like those in SensorML did me in, sorry.) John On Jan 14, 2013, at 18:20, Aleksandar Jelenak - NOAA Affiliate wrote: > Bruno, John: > > platform_azimuth_angle defines an angle where the observation point is > at the vertex, one side of the angle points north, the other side > points to the platform, and the angle is calculated clockwise from the > north. The observation point is defined by an instrument on the > platform. > > Here's one diagram explaining this angle: > http://science-edu.larc.nasa.gov/SCOOL/images/azimuth.gif > > platform_azimuth_angle in the diagram is labelled "Satellite Azimuth > from North". The observation target is labelled "Where You Are". > > I don't agree the definition is weak. It mentions that "platform" > means the vehicle from which *observations* are made, and clearly > indicates that *observation target* is at the vertex of this angle. > Perhaps the confusion is arising from the term "azimuth" as it is > widely used in ship and airplane navigation. > > I opted for "platform" in the name because I saw a standard name > platform_zenith_angle which can be applied to satellite zenith angles > and thought to complete the other two missing: satellite scan/look > angle and satellite azimuth angle by replacing "satellite" with > "platform". > > -Aleksandar > > > On Mon, Jan 14, 2013 at 12:29 PM, John Graybeal <jgrayb...@ucsd.edu> wrote: >> I agree with Bruno -- platform angle as it is defined in the request is the >> angle of the _platform_ with respect to a reference direction ("the >> horizontal angle between the line of sight from the observation point to the >> platform and a reference direction at the observation point, which is often >> due north"). The seems like platform orientation to me too. >> >> I wasn't excited about the name platform_azimuth_angle anyway, because it is >> ambiguous on this exact point -- is it the azimuth angle of the platform, or >> of the instrument on the platform? (the former, in this case). >> Platform_orientation seems to be the accepted name for the purpose. >> >> The definition is very weak though -- can we propose the substitution of >> this definition for that one? >> >> John >> >> On Jan 14, 2013, at 09:17, Bruno PIGUET wrote: >> >>> Le 14/01/2013 17:21, Aleksandar Jelenak - NOAA Affiliate a écrit : >>>> Dear Bruno, >>>> >>>> On Fri, Jan 11, 2013 at 11:52 AM, Bruno PIGUET <bruno.pig...@meteo.fr> >>>> wrote: >>>>> I have one remark about "platform_azimuth_angle" >>>>> >>>>> I like this name and it correspond to usual navigation definition (as >>>>> far as I can tell from my experience with airborne and shipborne >>>>> measurements), but... >>>>> >>>>> There is already a standard name called "platform_orientation", whose >>>>> definition seems to be the same, even if less precisely-worded : The >>>>> platform orientation is the direction in which the "front" or >>>>> longitudinal axis of the platform is pointing (not necessarily the same >>>>> as the direction in which it is travelling, called platform_course). >>>> >>>> platform_orientation is not the same as platform_azimuth_angle. This >>>> azimuth angle is related to measurements made by an instrument mounted >>>> on a platform (satellite, ship, airplane, truck, etc.). >>> >>> Sorry for looking dumb, but I don't see the difference (except that >>> "platform_orientation" is not precisely defined). >>> >>> I'm currently producing CF files containing airborne measurements, >>> and the parameter which is usually called "heading", which is in fact >>> exactly defined as "platform_azimuth_angle", is qualified with >>> "standard_name = platform orientation". >>> >>> Bruno. >>> -- >>> bruno.pig...@meteo.fr _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
