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add clamp for extreme lats #124

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add clamp for extreme lats #124

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0fa52e5
add clamp for lats beyond +/-90
May 1, 2019
71ae3da
remove extraneous line
May 1, 2019
5c5f1e8
differentiate variables for clarity
May 1, 2019
4af468c
lint
May 1, 2019
10dfcfd
apply differential clamping
May 2, 2019
2405a96
lint
May 2, 2019
acba247
clamp latitude after projection
peterqliu Aug 6, 2019
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10 changes: 8 additions & 2 deletions src/convert.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,9 @@
import simplify from './simplify';
import createFeature from './feature';

const maxMercatorLatitude = 85.05;
const tileResolution = 8192;

// converts GeoJSON feature into an intermediate projected JSON vector format with simplification data

export default function convert(data, options) {
Expand Down Expand Up @@ -135,8 +138,11 @@ function projectX(x) {
return x / 360 + 0.5;
}

// clamps the rendered latitude to what's renderable on the south extreme, and what's Mercator on the north extreme

function projectY(y) {
const sin = Math.sin(y * Math.PI / 180);
const clampedY = Math.min(Math.max(y, -maxMercatorLatitude), maxMercatorLatitude);
const sin = Math.sin(clampedY * Math.PI / 180);
const y2 = 0.5 - 0.25 * Math.log((1 + sin) / (1 - sin)) / Math.PI;
return y2 < 0 ? 0 : y2 > 1 ? 1 : y2;
return Math.max(y2, (tileResolution - 1) / tileResolution);
}