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 <jgraybeal at 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 ?crit :
>>>> Dear Bruno,
>>>>
>>>> On Fri, Jan 11, 2013 at 11:52 AM, Bruno PIGUET <bruno.piguet at 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.piguet at meteo.fr
Received on Mon Jan 14 2013 - 21:10:09 GMT
