splitLineWithPoints doesn't split correctly

[kudlav]

turf.lineSplit is not splitting properly large geometries, even after removing the square as suggested in #1232.

I have two cases. The first is on a scale of 1:100, and the second is 1:1 (original). For the first one, it returns 5 segments (correct), for the second one only 4 of 5 segments.

// 1:100
turf.lineSplit(
  {
    type: 'Feature',
    properties: {},
    geometry: {
      type: 'LineString',
      coordinates: [[14.14, 42.24], [9.92, 34.4], [11.44, 29.92], [9.76, 28.48], [1.44, 29.9], [-13.28, 27.04], [-34.04, 14.88], [-31.64, 7.2], [-22.56, 10.8], [-3.68, 4.1], [-6.22, -9.44], [-3.36, -12.2], [23.84, -11.02], [31.84, -6.7], [42.24, -7.5]],
    },
  },
  {
    type: 'Feature',
    properties: {},
    geometry: {
      type: 'Polygon',
      coordinates: [[[0, 0], [40.96, 0], [40.96, 18.62], [15.68, 5.16], [5.56, 27.7], [20.77, 35.69], [0, 40.96], [0, 0]]],
    },
  },
);

// 1:1
turf.lineSplit(
  {
    type: 'Feature',
    properties: {},
    geometry: {
      type: 'LineString',
      coordinates: [[1414, 4224], [992, 3440], [1144, 2992], [976, 2848], [144, 2990], [-1328, 2704], [-3404, 1488], [-3164, 720], [-2256, 1080], [-368, 410], [-622, -944], [-336, -1220], [2384, -1102], [3184, -670], [4224, -750]],
    },
  },
  {
    type: 'Feature',
    properties: {},
    geometry: {
      type: 'Polygon',
      coordinates: [[[0, 0], [4096, 0], [4096, 1862], [1568, 516], [556, 2770], [2077, 3569], [0, 4096], [0, 0]]],
    },
  },
);

The problem is in splitLineWithPoints function.
It gets correctly the same 4 intersections, the splitter parameter is:

// 1:100
[0, 29.62021739130434]
[7.710658597785979, 28.82976740278172]
[11.189808184780334, 30.657407455384277]
[11.834699005058457, 37.957165924089644]

// 1:1
[0, 2962.021739130435] }
[771.0658597785978, 2882.976740278172]
[1118.9808184780334, 3065.7407455384277]
[1183.4699005058458, 3795.7165924089645]

This code doesn't check if the closestLine was actually split into two lines. And, in my second case, when splitLineWithPoint splitting using point [771.0658597785978, 2882.976740278172], the splitLineWithPoint returns only one line instead of twos (the splitting or choosing the closestLine is broken).

turf/packages/turf-line-split/index.js

Lines 105 to 109 in c76e6e9

	// Append the two newly split lines into the results
	featureEach(splitLineWithPoint(closestLine, point), function (line) {
	results.push(line);
	tree.insert(line);
	});

@turf/turf v7.0.0-alpha.115
Node.js v20.11.1

[smallsaucepan]

Thanks for the detailed write up @kudlav. For the second example (which returns an incorrect result) I noticed the co-ordinates are outside what would typically be expected as valid geojson for Turf:

type: 'LineString',
      coordinates: [[1414, 4224], [992, 3440], [1144, 2992], ...

[lng, lat] respectively would typically be -180 to +180, and -90 to +90 decimal degrees. Can you run through your use case in more depth if those are the values you need to use? What is the significance of the scaling?

[kudlav]

Hi, you are right. I'm working out of WGS84 range. Other turf functions are fine with it. I'll normalize our range into WGS84 before using the splitLineWithPoints as a workaround.