Reference · Map projections for sky charts
projectfunction
Where a point of the sky lands on the chart.
With the default mirror: false the chart is the sky seen looking up: north is up and east is to the LEFT, so x grows toward decreasing right ascension. Set mirror: true for the map convention (east right).
y grows toward the north (up the chart).
Import it
import { project } from "@johnmorrisdotca/hoshi-stars/projection";Definition
function project(kind: Projection, point: SkyPoint, options: ProjectionOptions): MapPoint | undefinedParameters
| Name | Type | Description |
|---|---|---|
kind | "stereographic" | "orthographic" | "gnomonic" | "equidistant" | "equirectangular" | "mollweide" | "hammer" | The projection. |
point | SkyPoint | The sky position in degrees ( |
options | ProjectionOptions | The |
Returns
MapPoint | undefined
The point on the chart, or undefined when the sky position is not on the visible side: the far hemisphere of orthographic and gnomonic (90 degrees or more from the centre for gnomonic), and the antipode of the centre for stereographic.
Examples
import { project } from "@johnmorrisdotca/hoshi-stars/projection";
const orion = { centre: { rightAscension: 83.8, declination: -5.4 }, scale: 300 };
const betelgeuse = project("stereographic", { rightAscension: 88.79, declination: 7.41 }, orion);
console.log(betelgeuse); // left of the middle (it is east of the centre) and above it{ x: -26.25245580738588, y: 67.3739922582786 }What it prints (run when this page was built)