我有一个 MultiLineString，它由形成路径的各个 LineStrings 组成。路径有一个方向，必须对 LineStrings 进行排序以反映此顺序。为此，必须将某些字符串反转以指向与其余字符串相同的方向。 什么是合适的算法来完成这项任务？
换句话说，对列表进行排序的最佳方法是什么，列表可以颠倒？即
输入：
[2, 1] [4, 5] [0, 1] [5, 6] [9, 8]
输出：
[0, 1] [1, 2] [4, 5] [5, 6] [8, 9]
【问题讨论】：
标签： javascript python geojson multilinestring
Sorted() 带有列表理解
例如：
l = [[2, 1] ,[4, 5], [0, 1], [5, 6], [9, 8]]
print(sorted([sorted(i) for i in l]))
输出：
[[0, 1], [1, 2], [4, 5], [5, 6], [8, 9]]
【讨论】：
sorted。唯一可以应用于内部列表的操作是反向操作，算法应该决定是反向列表还是保持原样。
print(sorted([list(reversed(i)) for i in l]))
未能找到解决方案，我最终编写了这个算法。它可以完成这项工作，但可以更好地处理分支，即。选择会产生最长连续路径的分支。现在它只是坚持第一条线段并从那里开始。
给定一个 GeoJSON MultiLineString 几何，该算法将线段排序为连续路径并返回一个新几何。
代码已根据 Do What The F*ck You Want To Public License 获得许可。
import math
from collections import namedtuple
from operator import attrgetter
from copy import deepcopy
def arrange_geometry(original_geometry):
def distance(coords1, coords2):
return math.sqrt(math.pow(coords1[0] - coords2[0], 2) + math.pow(coords1[1] - coords2[1], 2))
MinDistance = namedtuple('MinDistance', 'target distance offset reverse_target')
geometry = deepcopy(original_geometry)
if geometry['type'] == 'MultiLineString':
lines = geometry['coordinates']
sorted_multistring = [lines.pop(0)]
while lines:
min_distances = []
for line in lines:
source_a = sorted_multistring[0][0]
source_b = sorted_multistring[-1][-1]
target_a = line[0]
target_b = line[-1]
distances = [
MinDistance(target=line, distance=distance(source_b, target_a), offset=1, reverse_target=False),
MinDistance(target=line, distance=distance(source_a, target_a), offset=-1, reverse_target=True),
MinDistance(target=line, distance=distance(source_b, target_b), offset=1, reverse_target=True),
MinDistance(target=line, distance=distance(source_a, target_b), offset=-1, reverse_target=False)
]
min_distance = min(distances, key=attrgetter('distance'))
min_distances.append(min_distance)
min_distance = min(min_distances, key=attrgetter('distance'))
target = min_distance.target
if min_distance.reverse_target:
target.reverse()
if min_distance.offset == 1:
sorted_multistring.append(target)
else:
sorted_multistring.insert(0, target)
lines.remove(target)
geometry['coordinates'] = sorted_multistring
return geometry
【讨论】：
即使问题需要 Python 解决方案，并且由于我通过 DuckDuckGo 搜索试图找到解决此问题的方法（对 GeoJson MultiLineString 几何上的段进行排序）到达此页面，我认为 Java / Kotlin到达这里的其他人可能会赞赏解决方案。
我最初想出了一个自己的解决方案，它恰好类似于@kissaprofeetta 的解决方案。虽然我有一些不同之处：
我添加了 GeoJson 文件的读取和排序后 GeoJson 的写入
import com.google.gson.Gson
import com.google.gson.GsonBuilder
import org.xml.sax.SAXException
import java.io.File
import java.io.IOException
import java.io.PrintWriter
import javax.xml.parsers.ParserConfigurationException
const val ADDITION_MODE_BEGINNING_TO_BEGINNING = 0
const val ADDITION_MODE_BEGINNING_TO_END = 1
const val ADDITION_MODE_END_TO_BEGINNING = 2
const val ADDITION_MODE_END_TO_END = 3
data class MultiLineString2(
val type: String,
val coordinates: ArrayList<ArrayList<ArrayList<Double>>>
)
fun sortSegmentsOfGeoJsonRoute(routeId: Int)
{
try {
val gson = GsonBuilder().setPrettyPrinting().create()
val geoJsonRoute = gson.fromJson(
File("src/main/assets/geojson/" + routeId + ".geojson").readText(),
MultiLineString2::class.java
)
val newTrackSegments = ArrayList<ArrayList<ArrayList<Double>>>()
newTrackSegments.add(geoJsonRoute.coordinates.first())
geoJsonRoute.coordinates.forEach { newSegment ->
if (!newTrackSegments.contains(newSegment)) {
var existingSegmentAsReference: ArrayList<ArrayList<Double>>? = null
var minDistanceToNewSegment = Double.MAX_VALUE
var additionMode = 0
newTrackSegments.forEach { existingSegment ->
val existingSegmentEnd = existingSegment.lastIndex
val newSegmentEnd = newSegment.lastIndex
val distFromBeginningToBeginning = distance(existingSegment[0][1], newSegment[0][1], existingSegment[0][0], newSegment[0][0])
val distFromBeginningToEnd = distance(existingSegment[0][1], newSegment[newSegmentEnd][1], existingSegment[0][0], newSegment[newSegmentEnd][0])
val distFromEndToBeginning = distance(existingSegment[existingSegmentEnd][1], newSegment[0][1], existingSegment[existingSegmentEnd][0], newSegment[0][0])
val distFromEndToEnd = distance(existingSegment[existingSegmentEnd][1], newSegment[newSegmentEnd][1], existingSegment[existingSegmentEnd][0], newSegment[newSegmentEnd][0])
var curMinDistance = Math.min(distFromBeginningToBeginning, distFromBeginningToEnd)
curMinDistance = Math.min(curMinDistance, distFromEndToBeginning)
curMinDistance = Math.min(curMinDistance, distFromEndToEnd)
if (curMinDistance <= minDistanceToNewSegment) {
minDistanceToNewSegment = curMinDistance
when (curMinDistance) {
distFromBeginningToBeginning -> additionMode = ADDITION_MODE_BEGINNING_TO_BEGINNING
distFromBeginningToEnd -> additionMode = ADDITION_MODE_BEGINNING_TO_END
distFromEndToBeginning -> additionMode = ADDITION_MODE_END_TO_BEGINNING
distFromEndToEnd -> additionMode = ADDITION_MODE_END_TO_END
}
existingSegmentAsReference = existingSegment
}
}
addTrackSegment(existingSegmentAsReference, additionMode, newSegment, newTrackSegments)
}
}
val sortedGeoJsonRoute = MultiLineString2("MultiLineString", newTrackSegments)
val geoJsonRouteWriter = PrintWriter("src/main/assets/geojson/" + routeId + "-sorted.geojson")
geoJsonRouteWriter.append(gson.toJson(sortedGeoJsonRoute))
geoJsonRouteWriter.close()
} catch (ex: ParserConfigurationException) { }
catch (ex: SAXException) { }
catch (ex: IOException) { }
catch (ex: Exception) {
print(ex.localizedMessage)
}
}
private fun addTrackSegment(
existingSegmentAsReference: ArrayList<ArrayList<Double>>?,
additionMode: Int,
newSegment: ArrayList<ArrayList<Double>>,
newTrackSegments: ArrayList<ArrayList<ArrayList<Double>>>
) {
if (existingSegmentAsReference != null) {
when (additionMode) {
ADDITION_MODE_BEGINNING_TO_BEGINNING -> {
val segmentToBeAdded = newSegment.reversed() as ArrayList<ArrayList<Double>>
val indexWhereToAddNewSegment = Math.max(0, newTrackSegments.indexOf(existingSegmentAsReference))
newTrackSegments.add(indexWhereToAddNewSegment, segmentToBeAdded)
}
ADDITION_MODE_BEGINNING_TO_END -> {
val indexWhereToAddNewSegment = Math.max(0, newTrackSegments.indexOf(existingSegmentAsReference))
newTrackSegments.add(indexWhereToAddNewSegment, newSegment)
}
ADDITION_MODE_END_TO_BEGINNING -> {
newTrackSegments.add(newSegment)
}
ADDITION_MODE_END_TO_END -> {
newTrackSegments.add(newSegment.reversed() as ArrayList<ArrayList<Double>>)
}
}
}
}
fun distance(lat1: Double, lat2: Double, lon1: Double, lon2: Double): Double
{
val earthRadius = 6371
val latDistance = Math.toRadians(lat2 - lat1)
val lonDistance = Math.toRadians(lon2 - lon1)
val a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2) + (Math.cos(Math.toRadians(lat1)) * Math.cos(
Math.toRadians(lat2)
) * Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2))
val c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))
val distance = earthRadius.toDouble() * c * 1000.0
/* If you add el1 and el2 parameters, as elevation, then you coud make this change to take it in account for the distance. You'll have to remove, obviously, the return line that is now below this multiline comment
val height = el1 - el2
distance = Math.pow(distance, 2.0) + Math.pow(height, 2.0)
return Math.sqrt(distance) */
return Math.sqrt(Math.pow(distance, 2.0))
}
【讨论】：