[FRIAM] Great Circle

[Steve Smith]

I'm imagining a post near-apocalyptic world where the near-future
MAGAmorlocks watch ElonMuskishEloi flying machines traveling high in the
sky (with or without contrails) and set their crude sextants on the
problem of shooting a trajectory and from that guestimating which known
megaCity Enclaves they are traveling between.  

Thanks to Barry for the Gnomonic projection prompt...  I seem to
remember that the Gnomonic is the earliest known map projection and is
derived from the traces of time-arcs cast by the sundial's gnomon.

Am I wrong that Rhumblines are reasonable approximations of great
circles, with the added convenience of providing a very simple
navigational technique (constant angle to north)?

    https://en.wikipedia.org/wiki/Rhumbline_network

turning the problem inside out (Ed Angel/SteveG), we have the
rectilinear lens?

    https://en.wikipedia.org/wiki/Rectilinear_lens


On 9/19/21 7:20 PM, Barry MacKichan wrote:
> In the northern hemisphere a great circle route between two points
> with the same latitude will be north of the parallel, so if the
> latitudes are close, the great circle will arch above the straight
> line (for most map projections that keep “parallels” parallel). A
> gnomonic projection of the world centered on Charlotte or Honolulu
> would show the great circle route as a straight line. I’m sure none of
> those were printed, but I thought I might find a site that allowed the
> user to select a tangent point (Charlotte or Honolulu) and then show
> the map. The closest I got was https://bl.ocks.org/mbostock/3795048
> <https://bl.ocks.org/mbostock/3795048> and https://observablehq.com/@d3/gnomonic 
> <https://observablehq.com/@d3/gnomonic>. It turns out that d3.js, a
> graphics library has a function geoGnomonic().
>
> —Barry
>
> Sent from my iPad
>
>> On Sep 19, 2021, at 3:50 PM, Frank Wimberly <wimberly3 at gmail.com> wrote:
>>
>> 
>> Not to change the subject but...
>>
>> A large airliner recently, 15 minutes ago, flew over Santa Fe headed
>> west.  My Flight Radar app tells me that it's a Boeing 777 going from
>> Charlotte to Honolulu at an altitude of 38000 feet.  I wouldn't have
>> thought that Santa Fe was on a great Circle route between those two
>> cities.  But maybe it is.
>>
>> ---
>> Frank C. Wimberly
>> 140 Calle Ojo Feliz,
>> Santa Fe, NM 87505
>>
>> 505 670-9918
>> Santa Fe, NM
>>
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