Reference · Framing, geometry and quiz tools
localConvergencefunction
The angle, in degrees, between true north and the canvas's up at a place: how much a thing that points at a true
bearing is turned on a local map. Zero on the central meridian, a few hundredths of a degree a kilometre or two east
or west of it; positive east of the centre in the northern hemisphere, where the meridians lean in towards the pole.
A marker at a bearing is turned by its bearing less this (localMap does it).
Import it
import { localConvergence } from "@johnmorrisdotca/chizu";Definition
function localConvergence(centre: readonly [number, number], lon: number, lat: number): numberParameters
| Name | Type | Description |
|---|---|---|
centre | readonly [number, number] | The centre of the local map, as [longitude, latitude] in degrees. |
lon | number | The longitude of the place, in degrees. |
lat | number | The latitude of the place, in degrees. |
Returns
number
The angle, in degrees, between the grid's north and true north there; positive east of the centre.
Examples
import { localConvergence } from "@johnmorrisdotca/chizu";
console.log(localConvergence([139.7671, 35.6812], 139.7671, 35.69), localConvergence([139.7671, 35.6812], 139.85, 35.69) > 0);
// 0 true0 trueWhat it prints (run when this page was built)