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calcZForBBox - add missing distance function

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Add distance function based on haversine formula (see
https://en.wikipedia.org/wiki/Haversine_formula )
This commit is contained in:
iom 2021-03-04 12:52:56 +01:00
parent af2b9f5c01
commit 29b2187af5
1 changed files with 18 additions and 4 deletions
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22
src/serve_rendered.js
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@ -27,6 +27,8 @@ const utils = require('./utils');
const FLOAT_PATTERN = '[+-]?(?:\\d+|\\d+\.?\\d+)'; const FLOAT_PATTERN = '[+-]?(?:\\d+|\\d+\.?\\d+)';
const httpTester = /^(http(s)?:)?\/\//; const httpTester = /^(http(s)?:)?\/\//;
const RADIUS_EARTH_EQUATORIAL_IN_M = 6378137;
const getScale = scale => (scale || '@1x').slice(1, 2) | 0; const getScale = scale => (scale || '@1x').slice(1, 2) | 0;
mbgl.on('message', e => { mbgl.on('message', e => {
@ -173,6 +175,19 @@ const renderOverlay = (z, x, y, bearing, pitch, w, h, scale,
return canvas.toBuffer(); return canvas.toBuffer();
}; };
const toRadian = (deg) => deg*Math.PI/180;
const getDistanceForPoints = (a, b) => {
// calculates great-circle distance between two points on a sphere in
// meters (see https://en.wikipedia.org/wiki/Haversine_formula)
const phi = [toRadian(a[1]), toRadian(b[1])]; // latitudes
const lambda = [toRadian(a[0]), toRadian(b[0])]; // longitudes
const h = (Math.sin((phi[1]-phi[0])/2))**2 +
Math.cos(phi[0]) * Math.cos(phi[1]) *
(Math.sin((lambda[1]-lambda[0])/2))**2;
return 2 * RADIUS_EARTH_EQUATORIAL_IN_M * Math.asin(Math.sqrt(h));
};
const calcZForBBox = (bbox, w, h, query) => { const calcZForBBox = (bbox, w, h, query) => {
// Use equation for horizontal distance per tile given zoom and latitude // Use equation for horizontal distance per tile given zoom and latitude
// see https://wiki.openstreetmap.org/wiki/Zoom_levels#Distance_per_pixel_math // see https://wiki.openstreetmap.org/wiki/Zoom_levels#Distance_per_pixel_math
@ -189,15 +204,14 @@ const calcZForBBox = (bbox, w, h, query) => {
// points (use centered latitude of bbox) // points (use centered latitude of bbox)
const latCenter = bbox[1]+(bbox[3]-bbox[1])/2; const latCenter = bbox[1]+(bbox[3]-bbox[1])/2;
const latRadian = latCenter*Math.PI/180;
const east = [bbox[0], latCenter]; const east = [bbox[0], latCenter];
const west = [bbox[2], latCenter]; const west = [bbox[2], latCenter];
// calculate zoom // calculate zoom
const distancePerPixel = haversine(east, west) / w; const distancePerPixel = getDistanceForPoints(east, west) / w;
const distancePerTile = distancePerPixel * 256; const distancePerTile = distancePerPixel * 256;
const circumferenceEarth = 2 * Math.PI * 6378137; const circumferenceEarth = 2 * Math.PI * RADIUS_EARTH_EQUATORIAL_IN_M;
const z = Math.log2(Math.abs(circumferenceEarth * Math.cos(latRadian) / distancePerTile)); const z = Math.log2(Math.abs(circumferenceEarth * Math.cos(toRadian(latCenter)) / distancePerTile));
// bounds enforcement [0,25] // bounds enforcement [0,25]
return Math.min(Math.abs(z), 25) return Math.min(Math.abs(z), 25)