I am currently doing gis business, so I need to operate the geometry object in postgis. I have found a lot of libraries, such as geotools, but I can't download it for some reason.
There is also jts, but it is not easy to use and very complicated to operate. Found another class library--geolatte-geom and geolatte-geojson.
Used to operate the conversion between geometry, String and json. My personal understanding of json and geojson is that the output formats are different. There are some more geometry-specific properties.
Mainly used to convert String into geometry objects, wkt and wkb are convenient and easy to use.
<!-- https://mvnrepository.com/artifact/org.geolatte/geolatte-geom -->
<dependency>
<groupId>org.geolatte</groupId>
<artifactId>geolatte-geom</artifactId>
<version>1.6.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.geolatte/geolatte-geojson -->
<dependency>
<groupId>org.geolatte</groupId>
<artifactId>geolatte-geojson</artifactId>
<version>1.6.0</version>
</dependency>public static void main(String[] args) {
// 模拟数据库中直接取出的geometry对象值（他是二进制的）
// WKT 是字符串形式，类似"POINT(1 2)"的形式
// 所以WKT转 geometry，相当于是字符串转geometry
// WKB转 geometry，相当于是字节转geometry
String s="01020000800200000097E5880801845C404D064F3AF4AE36400000000000000000290A915F01845C40DC90B1A051AE36400000000000000000";
Geometry geo = Wkb.fromWkb(ByteBuffer.from(s));
// geometry对象和WKT输出一致
// Geometry geometry1 = Wkt.fromWkt(wkt);
System.out.println("-----Geometry------"+geo.getPositionN(1));
System.out.println("-----wkt------"+ Wkt.toWkt(geo));
System.out.println("-----wkb------"+Wkb.toWkb(geo));
}Recently, because I need to save some longitude and latitude block information to the database, I used the Geometry attribute (geometry) in mysql object). I have collected a lot of information on the Internet, but there are still various problems when I actually use it, so I recommend a method that may be a bit stupid but practical (my usage environment springboot tool is sts). Here is an example to illustrate.
First understand what spatial data types are in the database
| Type | Description | Introduction | Example |
| Space data | Any space type | ||
| Point | Coordinate value | POINT(104.00924 30.46872) | |
| Line | Line is formed by connecting a series of points | LINESTRING(1 1, 1 1, 1 1) | |
| Polygon | is composed of multiple lines | POLYGON((1 1, 2 2, 3 3, 4 4, 5 5)) | |
| Point collection | Collection class, containing multiple points | MULTIPOINT(1 1, 2 2, 1 1) | |
| Line collection | Collection class, containing multiple lines | MULTILINESTRING((1 1, 2 2), (1 1, 1 1)) | |
| Polygon collection | Collection class, containing multiple polygons | MULTIPOLYGON(((0 0 , 1 0, 1 1, 0 1, 0 0)), ((1 1, 1 1, 1 1, 1 1, 1 1))) | |
| Spatial data collection | Collection class, which can include multiple points, lines, and polygons | GEOMETRYCOLLECTION(POINT(1 1), POINT(3 3), LINESTRING(1 1, 2 2)) |
When the data is ready, start preparing for the read operation.
Add dependencies for operating objects such as Geometry in pom.xml.
<dependency>
<groupId>com.vividsolutions</groupId>
<artifactId>jts</artifactId>
<version>1.13</version>
</dependency>Originally, I wanted to directly determine the type in the entity class and convert it directly to the object, but after using it, I found that it didn’t work, so I directly set it to Object. Binary is used to store Geometry in mysql, so I directly convert the binary Convert to Geometry object through jts.
//private Geometry geom; 不可行
private Object geomAsBytes; //可行 最终得到的是一个byte数组
//直接把数据库中的byte[]转Geometry对象
public static Geometry getGeometryByBytes( byte[] geometryAsBytes) throws Exception {
Geometry dbGeometry = null;
// 字节数组小于5，说明geometry有问题
if (geometryAsBytes.length < 5) {
return null;
}
//这里是取字节数组的前4个来解析srid
byte[] sridBytes = new byte[4];
System.arraycopy(geometryAsBytes, 0, sridBytes, 0, 4);
boolean bigEndian = (geometryAsBytes[4] == 0x00);
// 解析srid
int srid = 0;
if (bigEndian) {
for (int i = 0; i < sridBytes.length; i++) {
srid = (srid << 8) + (sridBytes[i] & 0xff);
}
} else {
for (int i = 0; i < sridBytes.length; i++) {
srid += (sridBytes[i] & 0xff) << (8 * i);
}
}
//use the JTS WKBReader for WKB parsing
WKBReader wkbReader = new WKBReader();
// 使用geotool的WKBReader 把字节数组转成geometry对象。
byte[] wkb = new byte[geometryAsBytes.length - 4];
System.arraycopy(geometryAsBytes, 4, wkb, 0, wkb.length);
dbGeometry = wkbReader.read(wkb);
dbGeometry.setSRID(srid);
return dbGeometry;
}Complete usage example, parse the geometry object in the database and get the point data we need.
//返回一个区域集合 区域由若干个点组成
public List < Area > geometryCollection2PressAreas(byte[] data) {
List < Area > areas= new ArrayList < > ();
try {
//解析出空间集合层
GeometryCollection geometryCollection = (GeometryCollection) GeometryUtil.getGeometryByBytes(data);
int geometrySize = geometryCollection.getNumGeometries();
for (int i1 = 0; i1 < geometrySize; i1++) {
try {
//解析出多边形集合层
MultiPolygon multiPolygon = (MultiPolygon) geometryCollection.getGeometryN(i1);
int size = (int) multiPolygon.getNumPoints();
for (int i = 0; i < size; i++) {
try {
//解析出多边形
Polygon polygon = (Polygon) multiPolygon.getGeometryN(i);
//解析出多边形中的多个点位
Coordinate[] coordinates2 = polygon.getCoordinates();
int size2 = coordinates2.length;
Area area = new Area();
area.area_pts = new ArrayList < > ();
for (int j = 0; j < size2; j++) {
//点位对象 就一个x，一个y数据
Point point = new Point();
point.x = coordinates2[j].x;
point.y = coordinates2[j].y;
//点位集合
area.area_pts.add(point);
}
areas.add(area);
} catch (Exception e) {
break;
}
}
} catch (Exception e) {
break;
}
}
} catch (Exception e) {
e.printStackTrace();
}
return areas;
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