Fabio/tileserver-gl
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Fix calcZForBBox

Browse source 
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
Show stats Download patch file Download diff file Expand all files Collapse all files

39
src/serve_rendered.js
View file

@ -174,24 +174,33 @@ const renderOverlay = (z, x, y, bearing, pitch, w, h, scale,
};
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 ?
parseFloat(query.padding) : 0.1;
// points (use centered latitude of bbox)
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),
maxCorner = mercator.px([bbox[2], bbox[1]], z);
const w_ = w / (1 + 2 * padding);
const h_ = h / (1 + 2 * padding);
// calculate zoom
const distancePerPixel = haversine(east, west) / w;
const distancePerTile = distancePerPixel * 256;
const circumferenceEarth = 2 * Math.PI * 6378137;
const z = Math.log2(Math.abs(circumferenceEarth * Math.cos(latRadian) / distancePerTile));
z -= Math.max(
Math.log((maxCorner[0] - minCorner[0]) / w_),
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;
// bounds enforcement [0,25]
return Math.min(Math.abs(z), 25)
};
const existingFonts = {};