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js: Fix exact conv again #42

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js: Fix exact conv again #42

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f99978f
js: Fix exact conv again
Artoria2e5 Dec 19, 2016
3f4d974
js: fix scope
Artoria2e5 Dec 19, 2016
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22 changes: 14 additions & 8 deletions javascript/transform.js
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Original file line number Diff line number Diff line change
Expand Up @@ -77,23 +77,29 @@ exports.gcj2wgs = gcj2wgs;
function gcj2wgs_exact(gcjLat, gcjLng) {
// newCoord = oldCoord = gcjCoord
var newLat = gcjLat, newLng = gcjLng;
var oldLat = newLat, oldLng = newLng;
var rough = gcj2wgs(gcjLat, gcjLng);
var oldLat = rough.lat, oldLng = rough.lng;
var threshold = 1e-6; // ~0.55 m equator & latitude
var i; // taken out of loop for debugging at i == 29

for (var i = 0; i < 30; i++) {
for (i = 0;
i < 30 && Math.max(Math.abs(oldLat - newLat), Math.abs(oldLng - newLng)) > threshold;
i++) {
// oldCoord = newCoord
oldLat = newLat;
oldLng = newLng;
// newCoord = gcjCoord - wgs_to_gcj_delta(newCoord)
var tmp = wgs2gcj(newLat, newLng);
// approx difference using gcj-space difference
newLat -= gcjLat - tmp.lat;
newLng -= gcjLng - tmp.lng;
// diffchk
if (Math.max(Math.abs(oldLat - newLat), Math.abs(oldLng - newLng)) < threshold) {
break;
}
newLat -= tmp.lat - gcjLat;
newLng -= tmp.lng - gcjLng;
}

// i == 29 usually means bad things
if (i == 29) {
console.warn("gcj2wgs_exact: Out of iterations. Bug?");
}

return {lat: newLat, lng: newLng};
}
exports.gcj2wgs_exact = gcj2wgs_exact;
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