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@stephanbogner
Last active November 13, 2017 14:03
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Removes the loops from a lineString (Test to outline a lineString without having weird overlaps) Please note that this algorithm is not optimized for performance. I recommend only using it in command line tools
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var ls = {
"type": "Feature",
"properties": {},
"geometry": {
"type": "LineString",
"coordinates": [
[23.37890625, 57.61010702068388],
[16.5234375, 53.225768435790194],
[23.37890625, 50.064191736659104],
[23.203125, 46.800059446787316],
[18.80859375, 26.745610382199022],
[14.589843749999998, 28.613459424004414],
[17.578125, 35.31736632923788],
[28.30078125, 33.137551192346145],
[30.585937499999996, 11.523087506868514],
[30.234375, -20.797201434306984],
[21.09375, -21.125497636606266],
[10.1953125, -13.752724664396975],
[11.074218749999998, -5.0909441750333855],
[13.18359375, -0.7031073524364783],
[18.10546875, 1.9332268264771233],
[22.67578125, 2.986927393334876],
[46.05468749999999, -7.536764322084078],
[63.28125, -8.581021215641842],
[64.86328125, -3.513421045640032],
[65.21484375, 2.986927393334876],
[60.64453125000001, 4.565473550710278],
[54.140625, 3.8642546157214084],
[51.67968749999999, 0.17578097424708533],
[51.15234375, -11.350796722383672],
[51.328125, -20.632784250388013],
[49.39453125, -33.7243396617476],
[50.09765625, -46.07323062540835],
[44.29687499999999, -48.224672649565186]
]
}
}
console.log(JSON.stringify(removeLoops(ls), null, 4));
function removeLoops(feature) {
var segments = turf.lineSegment(feature);
var hasIntersection = false;
for (var i = 0; i < segments.features.length - 2; i++) {
for (var j = i + 2; j < segments.features.length; j++) {
var line1 = turf.lineString(segments.features[i].geometry.coordinates);
var line2 = turf.lineString(segments.features[j].geometry.coordinates);
var intersect = turf.lineIntersect(line1, line2);
if (intersect.features.length > 0) {
var intersectionCoordinates = intersect.features[0].geometry.coordinates;
var throwAwayFromIndex = i + 1;
var throwAwayToIndex = j + 1;
var throwAwayNumber = throwAwayToIndex - throwAwayFromIndex;
segments.features.splice(throwAwayFromIndex, throwAwayNumber);
var newLineString = mergeLineStrings(segments);
newLineString.geometry.coordinates.splice(throwAwayFromIndex, 0, intersectionCoordinates);
return removeLoops(newLineString);
}
}
}
if (hasIntersection === false) {
return feature;
}
}
function mergeLineStrings(featureCollection) {
var lineString = JSON.parse(JSON.stringify(featureCollection.features[0]));
lineString.geometry.coordinates = [];
delete lineString.bbox;
delete lineString.id;
for (var i = 0; i < featureCollection.features.length; i++) {
var feature = featureCollection.features[i];
lineString.geometry.coordinates.push(feature.geometry.coordinates[0]);
}
lineString.geometry.coordinates.push(featureCollection.features[featureCollection.features.length - 1].geometry.coordinates[1]);
return lineString;
}
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