localMapfunction

A local map: the ground of a city or a venue, from caller-given GeoJSON and pictures, in a projection made for a small piece of the earth. Nothing is fetched and no map data is added: what is drawn is what is passed in, with the credit lines the caller passes. A unit of the canvas is metresPerUnit metres (default: the longer side over 1,000), stated in projection, so a distance on the canvas is a distance on the ground. projectPoint and unprojectPoint work on it, and mapBoxFromLocal and localCanvasFromBox hand over to and from a world or country map.

import { localMap } from "@johnmorrisdotca/chizu";

function localMap(options: ChizuLocalOptions): ChizuLocalMap

import { groundDistance, localMap, projectPoint } from "@johnmorrisdotca/chizu";

const map = localMap({ centre: [-0.2795, 51.556], widthMetres: 1000, metresPerUnit: 1 });
const a = projectPoint(map, -0.2795, 51.556)!;
const b = projectPoint(map, -0.2795, 51.557)!;
// 0.001° of latitude is 111 m, and the canvas is in metres.
console.log(Math.round(Math.hypot(b[0] - a[0], b[1] - a[1])), Math.round(groundDistance([-0.2795, 51.556], [-0.2795, 51.557])));
// 111 111

111 111