[FRIAM] Great Circle

[Barry MacKichan]

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 and 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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