我正在尝试使用JTS和postgis作为基于spring的后端。虽然我知道JTS的基础知识但我不知道如何实现
只需使用Java implementation的geographiclib - 我相信你想要GeodesicLine;然后使用JTS和postgis获取你在postgresql中生成的线串坐标。 JavaScript中的这个geodesic path example应该可以帮助您入门。
我编写了以下方法，它能够满足您的要求，并使用JTS LineSegment对象来计算分裂点：
public ArrayList<LineString> splitLineStringIntoParts(LineString ls, double length){
// result list for linestrings
ArrayList<LineString> resultList = new ArrayList();
// list for linesegments from input linestring
ArrayList<LineSegment> lineSegmentList = new ArrayList();
// create LineSegment objects from input linestring and add them to list
for(int i = 1; i < ls.getCoordinates().length; i++){
lineSegmentList.add(new LineSegment(ls.getCoordinates()[i-1], ls.getCoordinates()[i]));
}
LineString currentLineString = null;
double neededLength = length;
for(LineSegment s : lineSegmentList){
while(s.getLength() > 0){
// case: current segment is small enough to be added to the linestring
if(s.getLength() <= neededLength){
// create linestring if it does not exist
if(currentLineString == null){
currentLineString = new GeometryFactory().createLineString(new Coordinate[]{new Coordinate(s.p0), new Coordinate(s.p1)});
// just add the new endpoint otherwise
} else {
Coordinate[] coords = new Coordinate[currentLineString.getCoordinates().length + 1];
// copy old coordinates
System.arraycopy(currentLineString.getCoordinates(), 0, coords, 0, currentLineString.getCoordinates().length);
// add new coordinate at the end
coords[coords.length-1] = new Coordinate(s.p1);
// create new linestring
currentLineString = new GeometryFactory().createLineString(coords);
}
neededLength -= s.getLength();
s.setCoordinates(s.p1, s.p1);
// add linestring to result list if needed length is 0
if(neededLength == 0){
resultList.add(currentLineString);
currentLineString = null;
neededLength = length;
}
// current segment needs to be cut and added to the linestring
} else {
// get coordinate at desired distance (endpoint of linestring)
Coordinate endPoint = s.pointAlong(neededLength/s.getLength());
// create linestring if it does not exist
if(currentLineString == null){
currentLineString = new GeometryFactory().createLineString(new Coordinate[]{new Coordinate(s.p0), endPoint});
// just add the new endpoint otherwise
} else {
// add new coordinate to linestring
Coordinate[] coords = new Coordinate[currentLineString.getCoordinates().length + 1];
// copy old coordinates
System.arraycopy(currentLineString.getCoordinates(), 0, coords, 0, currentLineString.getCoordinates().length);
// add new coordinate at the end
coords[coords.length-1] = endPoint;
currentLineString = new GeometryFactory().createLineString(coords);
}
// add linestring to result list
resultList.add(currentLineString);
// reset needed length
neededLength = length;
// reset current linestring
currentLineString = null;
// adjust segment (calculated endpoint is the new startpoint)
s.setCoordinates(endPoint, s.p1);
}
}
}
// add last linestring if there is a rest
if(neededLength < length){
resultList.add(currentLineString);
}
return resultList;
}
我还需要编写split函数，所以我在stackoverflow上找到解决方案，但找不到一些有用的信息。所以我写了follow方法并回答你的问题;
public List<LineString> lineSplit(LineString lineString,double meters) {
List<LineString> results = new ArrayList<>();
List<LineSegment> segments = new ArrayList<>();
// first split linestring to segements[]
for(int i = 1; i < lineString.getCoordinates().length; i++){
segments.add(new LineSegment(lineString.getCoordinates()[i-1], lineString.getCoordinates()[i]));
}
// remainLegnth means that last segment's length dont enough to split to one segement which length is meters
// neededLength means that current segment need how many meters to create a new segment
double remainLength = 0D;
double neededLength = 0D;
// remainCoors means that if the last iteartor dont create a new segment,also mean last segment
// is too short ,even add remains length can't create a new segment;so, we should add this segment's start
// point and end point to remainCoors
List<Coordinate> remainCoors = new ArrayList<>();
// netxStartPoint to store the next segment's start point
Coordinate netxStartPoint = null;
for(int i=0;i<segments.size();i++) {
LineSegment seg = segments.get(i);
neededLength = meters-remainLength;
remainLength += seg.getLength();
netxStartPoint = seg.p0;
while(remainLength>=meters) {
remainCoors.add(netxStartPoint);
Coordinate endPoint = seg.pointAlong(neededLength/seg.getLength());
// to remove the adjacent and same vertx
for(int j=0;j<remainCoors.size()-1;j++) {
if(remainCoors.get(j).equals(remainCoors.get(j+1))) {
remainCoors.remove(j);
}
}
remainCoors.add(endPoint);
results.add(lineString.getFactory().createLineString(remainCoors.toArray(new Coordinate[remainCoors.size()])));
remainCoors = new ArrayList<>();
netxStartPoint = endPoint;
remainLength -= meters;
neededLength += meters;
}
remainCoors.add(netxStartPoint);
remainCoors.add(seg.p1);
}
for(int j=0;j<remainCoors.size()-1;j++) {
if(remainCoors.get(j).equals(remainCoors.get(j+1))) {
remainCoors.remove(j);
}
}
if(remainCoors.size()>=2) {
results.add(lineString.getFactory().createLineString(remainCoors.toArray(new Coordinate[remainCoors.size()])));
}
return results;
}