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Fix calcZForBBox

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Static image rendering moves bbox (wrong zoom level by calcZForBBox).
This changesets calculates the correct zoom level for a given bounding
box.

See maptiler/tileserver-gl#490
This commit is contained in:
Kohl Listi 2021-03-04 00:28:12 +01:00 committed by iom
parent c89a5ae029
commit af2b9f5c01
1 changed files with 24 additions and 15 deletions
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39
src/serve_rendered.js
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@ -174,24 +174,33 @@ const renderOverlay = (z, x, y, bearing, pitch, w, h, scale,
}; };
const calcZForBBox = (bbox, w, h, query) => { const calcZForBBox = (bbox, w, h, query) => {
let z = 25; // Use equation for horizontal distance per tile given zoom and latitude
// see https://wiki.openstreetmap.org/wiki/Zoom_levels#Distance_per_pixel_math
//
// S_pixel * T = S_tile = C * cos(l) / (2^z) =
// S_tile := horizontal distance per tile
// S_pixel := horizontal distance per pixel
// T := tile size
// C := Equatorial circumference of Earth
// l := centered latitude of bbox
// z := zoom level
//
// => z = log2( C * cos(l) / (S_pixel*T) )
const padding = query.padding !== undefined ? // points (use centered latitude of bbox)
parseFloat(query.padding) : 0.1; const latCenter = bbox[1]+(bbox[3]-bbox[1])/2;
const latRadian = latCenter*Math.PI/180;
const east = [bbox[0], latCenter];
const west = [bbox[2], latCenter];
const minCorner = mercator.px([bbox[0], bbox[3]], z), // calculate zoom
maxCorner = mercator.px([bbox[2], bbox[1]], z); const distancePerPixel = haversine(east, west) / w;
const w_ = w / (1 + 2 * padding); const distancePerTile = distancePerPixel * 256;
const h_ = h / (1 + 2 * padding); const circumferenceEarth = 2 * Math.PI * 6378137;
const z = Math.log2(Math.abs(circumferenceEarth * Math.cos(latRadian) / distancePerTile));
z -= Math.max( // bounds enforcement [0,25]
Math.log((maxCorner[0] - minCorner[0]) / w_), return Math.min(Math.abs(z), 25)
Math.log((maxCorner[1] - minCorner[1]) / h_)
) / Math.LN2;
z = Math.max(Math.log(Math.max(w, h) / 256) / Math.LN2, Math.min(25, z));
return z;
}; };
const existingFonts = {}; const existingFonts = {};