空间计算操作

概述

空间计算操作是对几何对象进行各种空间运算，生成新的几何对象。本章介绍常用的空间计算操作，包括缓冲区分析、叠加分析、几何简化等。

缓冲区分析

基本缓冲区

缓冲区是围绕几何对象指定距离的区域：

/*** 获取几何缓冲区* @param geom 几何对象* @param distance 缓冲区距离（坐标系单位）*/
public static Geometry buffer(Geometry geom, double distance) {return geom.buffer(distance);
}

使用示例：

// 点缓冲区：生成圆形
Point point = factory.createPoint(new Coordinate(100, 100));
Geometry circle = buffer(point, 50);// 线缓冲区：生成条带状区域
LineString line = factory.createLineString(coords);
Geometry corridor = buffer(line, 10);// 面缓冲区：生成扩大的面
Polygon polygon = factory.createPolygon(shell);
Geometry expanded = buffer(polygon, 20);

负值缓冲区：

// 负值缓冲区会向内收缩
Geometry shrunk = buffer(polygon, -5);

ESRI几何引擎缓冲区

/*** 使用ESRI引擎计算缓冲区*/
public static String buffer(String wkt, Integer wkid, double distance) {Geometry geom = EsriUtil.createGeometryByWkt(wkt);SpatialReference sr = SpatialReference.create(wkid);Geometry buffer = OperatorBuffer.local().execute(geom, sr, distance, null);return EsriUtil.getWktStr(buffer);
}

缓冲区注意事项

坐标系影响：

地理坐标系：距离单位为度，结果在两极和赤道处变形不同
投影坐标系：距离单位为米，结果更准确

推荐做法：

// 先转换到投影坐标系
int projWkid = CrsUtil.getProjectedWkid(geom);
Geometry projGeom = CrsUtil.transform(geom, 4490, projWkid);// 在投影坐标系下做缓冲区
Geometry buffer = projGeom.buffer(distance);// 如需要，转回地理坐标系
Geometry geoBuffer = CrsUtil.transform(buffer, projWkid, 4490);

叠加分析

交集（Intersection）

获取两个几何对象的公共部分：

/*** 获取几何交集*/
public static Geometry intersection(Geometry a, Geometry b) {return a.intersection(b);
}

应用场景：

裁剪：按边界裁剪数据
统计：计算重叠面积
提取：提取两个图层的公共区域

并集（Union）

合并多个几何对象：

/*** 获取几何并集*/
public static Geometry union(Geometry... geoms) {Geometry result = null;for (Geometry g : geoms) {if (result == null) {result = g;} else {result = result.union(g);}}return result;
}

应用场景：

合并相邻地块
溶解（Dissolve）操作
生成复合区域

差集（Difference）

从一个几何中减去另一个几何：

/*** 获取A与B并集擦除B的部分* 结果为A中不与B重叠的部分*/
public static Geometry difference(Geometry a, Geometry b) {return a.difference(b);
}

应用场景：

擦除操作：从区域中移除指定部分
挖洞：在多边形中创建岛洞
更新：用新数据替换旧数据的部分区域

对称差集（Symmetric Difference）

获取两个几何不重叠的部分：

/*** 获取A与B并集减去A与B交集* 结果为A和B各自独有的部分*/
public static Geometry symDifference(Geometry a, Geometry b) {return a.symDifference(b);
}

应用场景：

找出两个版本数据的差异区域
识别变化区域

ESRI引擎叠加操作

/*** 计算几何的交集*/
public static String intersection(String awkt, String bwkt, Integer wkid) {Geometry a = EsriUtil.createGeometryByWkt(awkt);Geometry b = EsriUtil.createGeometryByWkt(bwkt);SpatialReference sr = SpatialReference.create(wkid);Geometry intersection = OperatorIntersection.local().execute(a, b, sr, null);return EsriUtil.getWktStr(intersection);
}/*** 计算几何的并集*/
public static String union(List<String> wkts, Integer wkid) {Geometry[] geoms = wkts.stream().map(EsriUtil::createGeometryByWkt).toArray(Geometry[]::new);SpatialReference sr = SpatialReference.create(wkid);Geometry union = GeometryEngine.union(geoms, sr);return EsriUtil.getWktStr(union);
}/*** 获取A与B并集擦除B的部分*/
public static String difference(String awkt, String bwkt, Integer wkid) {Geometry a = EsriUtil.createGeometryByWkt(awkt);Geometry b = EsriUtil.createGeometryByWkt(bwkt);SpatialReference sr = SpatialReference.create(wkid);Geometry difference = OperatorDifference.local().execute(a, b, sr, null);return EsriUtil.getWktStr(difference);
}

凸包与凹包

凸包（Convex Hull）

凸包是包围几何的最小凸多边形：

/*** 获取几何凸包*/
public static Geometry convexHull(Geometry geom) {ConvexHull ch = new ConvexHull(geom);return ch.getConvexHull();
}

特点：凸包没有任何凹陷，像是用橡皮筋围住所有点。

凹包（Concave Hull）

凹包是更紧密地包围几何的边界：

/*** 获取几何凹包*/
public static Geometry concaveHull(Geometry geom) {ConcaveHull ch = new ConcaveHull(geom);return ch.getHull();
}

特点：凹包会沿着点集的边缘形成凹陷。

ESRI引擎凸包：

/*** 计算几何的凸包*/
public static String convexHull(String wkt) {Geometry geom = EsriUtil.createGeometryByWkt(wkt);Geometry convexHull = OperatorConvexHull.local().execute(geom, null);return EsriUtil.getWktStr(convexHull);
}

几何简化

Douglas-Peucker简化

减少几何的节点数量，同时保持形状特征：

/*** 简化几何* @param distance 简化容差，越大简化程度越高*/
public static Geometry simplify(Geometry geom, double distance) {return DouglasPeuckerSimplifier.simplify(geom, distance);
}

应用场景：

数据压缩：减少数据量
地图显示：不同比例尺显示不同详细程度
性能优化：简化复杂几何提升计算速度

ESRI引擎简化

/*** 简化几何*/
public static String simplify(String wkt, Integer wkid) {Geometry geom = EsriUtil.createGeometryByWkt(wkt);SpatialReference sr = SpatialReference.create(wkid);Geometry simplified = OperatorSimplifyOGC.local().execute(geom, sr, false, null);return EsriUtil.getWktStr(simplified);
}

几何增密

增加节点密度

在几何的边上添加额外的节点：

/*** 增加几何节点密度* @param distance 节点间最大距离*/
public static Geometry densify(Geometry geom, double distance) {return Densifier.densify(geom, distance);
}

应用场景：

坐标转换前的预处理：防止长边在投影后变形
曲线拟合：为曲线化操作做准备

多边形化

从线生成面

将线几何转换为多边形：

/*** 多边形化几何*/
public static Geometry polygonize(Geometry geom) {List lines = LineStringExtracter.getLines(geom);Polygonizer polygonizer = new Polygonizer();polygonizer.add(lines);Collection polys = polygonizer.getPolygons();Polygon[] polyArray = GeometryFactory.toPolygonArray(polys);return geom.getFactory().createGeometryCollection(polyArray);
}

应用场景：

从道路网络生成地块
从边界线生成区域

切割操作

用线切割多边形

/*** 按照给定线切割多边形*/
public static Geometry splitPolygon(Geometry polygon, LineString line) {// 将切割线与多边形边界合并Geometry nodedLinework = polygon.getBoundary().union(line);// 多边形化Geometry polys = polygonize(nodedLinework);// 筛选在原多边形内部的部分List<Polygon> output = new ArrayList<>();for (int i = 0; i < polys.getNumGeometries(); i++) {Polygon candpoly = (Polygon) polys.getGeometryN(i);if (polygon.contains(candpoly.getInteriorPoint())) {output.add(candpoly);}}return polygon.getFactory().createGeometryCollection(GeometryFactory.toGeometryArray(output));
}

应用场景：

地块分割
区域划分

实践案例

案例1：缓冲区分析

计算道路两侧一定范围内的影响区域：

/*** 道路缓冲区分析*/
public WktLayer roadBufferAnalysis(WktLayer roadLayer, double bufferDistance) {WktLayer resultLayer = new WktLayer();resultLayer.setYwName("road_buffer");resultLayer.setWkid(roadLayer.getWkid());resultLayer.setGeometryType(GeometryType.POLYGON);resultLayer.setFields(roadLayer.getFields());List<WktFeature> features = new ArrayList<>();// 转换到投影坐标系int projWkid = CrsUtil.getProjectedWkid(38);  // 假设38带WktLayer projLayer = CrsUtil.reproject(roadLayer, projWkid);for (WktFeature feature : projLayer.getFeatures()) {Geometry geom = GeometryConverter.wkt2Geometry(feature.getWkt());Geometry buffer = geom.buffer(bufferDistance);WktFeature bufferFeature = new WktFeature();bufferFeature.setWfId(feature.getWfId());bufferFeature.setWkt(buffer.toText());bufferFeature.setFieldValues(feature.getFieldValues());features.add(bufferFeature);}resultLayer.setFeatures(features);// 转回原坐标系return CrsUtil.reproject(resultLayer, roadLayer.getWkid());
}

案例2：图层叠加分析

计算两个图层的重叠区域：

/*** 图层叠加分析*/
public WktLayer overlayAnalysis(WktLayer layer1, WktLayer layer2) {WktLayer resultLayer = new WktLayer();resultLayer.setYwName("overlay_result");resultLayer.setWkid(layer1.getWkid());resultLayer.setGeometryType(GeometryType.POLYGON);// 合并两个图层的字段List<WktField> fields = new ArrayList<>();fields.addAll(layer1.getFields());for (WktField field : layer2.getFields()) {field.setYwName("L2_" + field.getYwName());  // 避免字段名冲突fields.add(field);}resultLayer.setFields(fields);List<WktFeature> features = new ArrayList<>();for (WktFeature f1 : layer1.getFeatures()) {Geometry g1 = GeometryConverter.wkt2Geometry(f1.getWkt());for (WktFeature f2 : layer2.getFeatures()) {Geometry g2 = GeometryConverter.wkt2Geometry(f2.getWkt());// 判断是否相交if (g1.intersects(g2)) {// 计算交集Geometry intersection = g1.intersection(g2);if (!intersection.isEmpty() && intersection.getArea() > 0) {WktFeature feature = new WktFeature();feature.setWfId(f1.getWfId() + "_" + f2.getWfId());feature.setWkt(intersection.toText());// 合并属性值List<WktFieldValue> values = new ArrayList<>();values.addAll(f1.getFieldValues());values.addAll(f2.getFieldValues());feature.setFieldValues(values);features.add(feature);}}}}resultLayer.setFeatures(features);return resultLayer;
}

案例3：地块合并

合并相邻的地块：

/*** 合并相邻地块*/
public String mergeAdjacentParcels(List<String> wkts) {List<Geometry> geoms = wkts.stream().map(GeometryConverter::wkt2Geometry).collect(Collectors.toList());// 使用并集操作合并Geometry merged = union(geoms.toArray(new Geometry[0]));return GeometryConverter.geometry2Wkt(merged);
}

案例4：区域裁剪

按行政区边界裁剪数据：

/*** 区域裁剪*/
public WktLayer clipByBoundary(WktLayer dataLayer, String boundaryWkt) {Geometry boundary = GeometryConverter.wkt2Geometry(boundaryWkt);WktLayer resultLayer = new WktLayer();resultLayer.setYwName(dataLayer.getYwName() + "_clipped");resultLayer.setWkid(dataLayer.getWkid());resultLayer.setGeometryType(dataLayer.getGeometryType());resultLayer.setFields(dataLayer.getFields());List<WktFeature> features = new ArrayList<>();for (WktFeature feature : dataLayer.getFeatures()) {Geometry geom = GeometryConverter.wkt2Geometry(feature.getWkt());if (geom.intersects(boundary)) {Geometry clipped = geom.intersection(boundary);if (!clipped.isEmpty()) {WktFeature clippedFeature = new WktFeature();clippedFeature.setWfId(feature.getWfId());clippedFeature.setWkt(clipped.toText());clippedFeature.setFieldValues(feature.getFieldValues());features.add(clippedFeature);}}}resultLayer.setFeatures(features);return resultLayer;
}

案例5：多比例尺数据生成

为不同显示比例尺生成不同详细程度的数据：

/*** 生成多比例尺数据*/
public Map<String, WktLayer> generateMultiScaleData(WktLayer sourceLayer) {Map<String, WktLayer> result = new HashMap<>();// 原始数据result.put("1:1000", sourceLayer);// 简化程度：根据比例尺确定容差double[] tolerances = {0.1, 0.5, 1.0, 5.0};String[] scales = {"1:5000", "1:10000", "1:50000", "1:100000"};for (int i = 0; i < tolerances.length; i++) {WktLayer simplifiedLayer = simplifyLayer(sourceLayer, tolerances[i]);simplifiedLayer.setYwName(sourceLayer.getYwName() + "_" + scales[i]);result.put(scales[i], simplifiedLayer);}return result;
}private WktLayer simplifyLayer(WktLayer layer, double tolerance) {WktLayer result = new WktLayer();result.setYwName(layer.getYwName());result.setWkid(layer.getWkid());result.setGeometryType(layer.getGeometryType());result.setFields(layer.getFields());List<WktFeature> features = new ArrayList<>();for (WktFeature feature : layer.getFeatures()) {Geometry geom = GeometryConverter.wkt2Geometry(feature.getWkt());Geometry simplified = simplify(geom, tolerance);WktFeature simplifiedFeature = new WktFeature();simplifiedFeature.setWfId(feature.getWfId());simplifiedFeature.setWkt(simplified.toText());simplifiedFeature.setFieldValues(feature.getFieldValues());features.add(simplifiedFeature);}result.setFeatures(features);return result;
}