1. 原理
- Java对轨迹抽稀：道格拉斯普克算法
- 生成mvt瓦片：VectorTileEncoder.addFeature
2. pom依赖
<!-- geometry相关类 -->
<dependency>
<groupId>com.vividsolutions</groupId>
<artifactId>jts-core</artifactId>
<version>1.17.1</version>
</dependency>
<dependency>
<groupId>com.vividsolutions</groupId>
<artifactId>jts-core</artifactId>
<version>1.14.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.70</version>
</dependency>
<!-- vectorTile -->
<dependency>
<groupId>no.ecc.vectortile</groupId>
<artifactId>java-vector-tile</artifactId>
<version>1.2.1</version>
</dependency>
注意 locationtech 和 vividsolutions有的类名完全一致
import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.LineString;
import org.locationtech.jts.geom.LinearRing;
import org.locationtech.jts.geom.Point;
3. Java对轨迹道格拉斯普克抽稀源码
package no.ecc.vectortile;
import com.alibaba.fastjson.JSON;
import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.GeometryFactory;
import com.vividsolutions.jts.simplify.DouglasPeuckerSimplifier;
import java.util.*;
/*************************************
*Class Name:Doulag
*Description:<道格拉斯普克抽稀>
*@author:Seminar
*@create:2021/1/14
*@since 1.0.0
*************************************/
public class Doulag {
/**
* 计算两点距离
*
* @param point1
* @param point2
* @return
*/
private static double calculationDistance(double[] point1, double[] point2) {
double lat1 = point1[0];
double lat2 = point2[0];
double lng1 = point1[1];
double lng2 = point2[1];
double radLat1 = lat1 * Math.PI / 180.0;
double radLat2 = lat2 * Math.PI / 180.0;
double a = radLat1 - radLat2;
double b = (lng1 * Math.PI / 180.0) - (lng2 * Math.PI / 180.0);
double s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2)
+ Math.cos(radLat1) * Math.cos(radLat2) * Math.pow(Math.sin(b / 2), 2)));
return s * 6370996.81;
}
/**
* 计算点pX到点pA和pB所确定的直线的距离
*
* @param start
* @param end
* @param center
* @return
*/
private static double distToSegment(double[] start, double[] end, double[] center) {
double a = Math.abs(calculationDistance(start, end));
double b = Math.abs(calculationDistance(start, center));
double c = Math.abs(calculationDistance(end, center));
double p = (a + b + c) / 2.0;
double s = Math.sqrt(Math.abs(p * (p - a) * (p - b) * (p - c)));
return s * 2.0 / a;
}
/**
* 递归方式压缩轨迹
*
* @param coordinate
* @param result
* @param start
* @param end
* @param dMax
* @return
*/
private static List<double[]> compressLine(List<double[]> coordinate, List<double[]> result, int start, int end, int dMax) {
if (start < end) {
double maxDist = 0;
int currentIndex = 0;
double[] startPoint = coordinate.get(start);
double[] endPoint = coordinate.get(end);
for (int i = start + 1; i < end; i++) {
double currentDist = distToSegment(startPoint, endPoint, coordinate.get(i));
if (currentDist > maxDist) {
maxDist = currentDist;
currentIndex = i;
}
}
if (maxDist >= dMax) {
//将当前点加入到过滤数组中
result.add(coordinate.get(currentIndex));
//将原来的线段以当前点为中心拆成两段，分别进行递归处理
compressLine(coordinate, result, start, currentIndex, dMax);
compressLine(coordinate, result, currentIndex + 1, end, dMax);
} else {
result.remove(endPoint);
}
}
return result;
}
/**
* @param coordinate 原始轨迹Array<{latitude,longitude}>
* @param dMax 允许最大距离误差
* @return douglasResult 抽稀后的轨迹
*/
public static List<double[]> douglasPeucker(List<double[]> coordinate, int dMax) {
//抽稀点数量需要大于2
if (coordinate == null || coordinate.size() <= 2) {
return null;
}
List<double[]> coordinate2 = new ArrayList<>();
for (int i = 0; i < coordinate.size(); i++) {
double[] point = Arrays.copyOf(coordinate.get(i), 3);
point[2] = i;
coordinate2.add(point);
}
List<double[]> result = new ArrayList<>();
result = compressLine(coordinate2, result, 0, coordinate2.size() - 1, dMax);
result.add(coordinate2.get(0));
result.add(coordinate2.get(coordinate.size() - 1));
Collections.sort(result, new Comparator<double[]>() {
@Override
public int compare(double[] u1, double[] u2) {
if (u1[2] > u2[2]) {
return 1;
} else if (u1[2] < u2[2]) {
return -1;
}
return 0; //相等为0
}
});
return result;
}
public static void main(String[] args) {
GeometryFactory gf = new GeometryFactory();
Coordinate c1 = new Coordinate(1, 1.4);
Coordinate c2 = new Coordinate(1, 1.5);
Coordinate c3 = new Coordinate(1, 1.6);
Coordinate c4 = new Coordinate(10, 100);
Coordinate c5 = new Coordinate(100, 200);
double dinstanceTolerance = 1;
Geometry geometry = gf.createLineString(new Coordinate[]{c1, c2, c3, c4, c5});
// 使用原来jar包中带的方法
Geometry g1 = DouglasPeuckerSimplifier.simplify(geometry, dinstanceTolerance); // 1米范围内的点抽稀掉，还可为其他值double类型
System.out.println("g1: " + g1.getGeometryType().toString());
System.out.println("g1Coordinates size: " + g1.getCoordinates().length);
System.out.println("g1Coordinates: " + JSON.toJSONString(g1.getCoordinates()));
// 使用自己写的方法
List<double[]> coordinates = new ArrayList<>();
coordinates.add(new double[]{1d, 1.4d});
coordinates.add(new double[]{1d, 1.5d});
coordinates.add(new double[]{1d, 1.6d});
coordinates.add(new double[]{10d, 100d});
coordinates.add(new double[]{100d, 200d});
List<double[]> res = douglasPeucker(coordinates, 1);
System.out.println("douglasPeucker size: " + res.size());
System.out.println("g1Coordinates: " + JSON.toJSONString(res));
}
}
4. Java生成线瓦片源码
package no.ecc.vectortile;
import junit.framework.TestCase;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryFactory;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
public class VectorTileDecoderTest extends TestCase {
private GeometryFactory gf = new GeometryFactory();
public void testLineString() throws IOException {
Coordinate c1 = new Coordinate(1, 2);
Coordinate c2 = new Coordinate(10, 20);
Coordinate c3 = new Coordinate(100, 200);
Geometry geometry = gf.createLineString(new Coordinate[]{c1, c2, c3});
Map<String, Object> attributes = new HashMap<String, Object>();
attributes.put("aa", "bb");
attributes.put("cc", "bb");
String layerName = "layer";
VectorTileEncoder e = new VectorTileEncoder(4096, 16, false);
e.addFeature(layerName, attributes, geometry);
byte[] encoded = e.encode();
VectorTileDecoder d = new VectorTileDecoder();
assertEquals(1, d.decode(encoded).getLayerNames().size());
assertEquals(layerName, d.decode(encoded).getLayerNames().iterator().next());
assertEquals(attributes, d.decode(encoded, layerName).asList().get(0).getAttributes());
assertEquals(geometry, d.decode(encoded, layerName).asList().get(0).getGeometry());
}
}
参考
