WKT、WKB和GeoJson
1. 简介
- WKT(Well-known text)是开放地理空间联盟OGC（Open GIS Consortium ）制定的一种文本标记语言，用于表示矢量几何对象、空间参照系统及空间参照系统之间的转换。
- WKB(well-known binary) 是WKT的二进制表示形式，解决了WKT表达方式冗余的问题，便于传输和在数据库中存储相同的信息
- GeoJSON 一种JSON格式的Feature信息输出格式，它便于被JavaScript等脚本语言处理，OpenLayers等地理库便是采用GeoJSON格式。此外，TopoJSON等更精简的扩展格式
2. WKT
WKT可以表示的对象包括以下几种：
Point, MultiPoint
LineString, MultiLineString
Polygon, MultiPolygon
GeometryCollection
可以由多种Geometry组成，如：GEOMETRYCOLLECTION(POINT(4 6),LINESTRING(4 6,7 10)
| Type | WKT | GeoJSON |
|---|---|---|
| Point | POINT (30 10) | { “type”: “Point”, “coordinates”: [30, 10] } |
| LineString | LINESTRING (30 10, 10 30, 40 40) | { “type”: “LineString”, “coordinates”: [ [30, 10], [10, 30], [40, 40] ] } |
| Polygon | POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10)) | { “type”: “Polygon”, “coordinates”: [ [[30, 10], [40, 40], [20, 40], [10, 20], [30, 10]] ] } |
| Polygon | POLYGON ((35 10, 45 45, 15 40, 10 20, 35 10),(20 30, 35 35, 30 20, 20 30)) | { “type”: “Polygon”, “coordinates”: [ [[35, 10], [45, 45], [15, 40], [10, 20], [35, 10]], [[20, 30], [35, 35], [30, 20], [20, 30]] ] } |
| MultiPoint | MULTIPOINT ((10 40), (40 30), (20 20), (30 10)) | { “type”: “MultiPoint”, “coordinates”: [ [10, 40], [40, 30], [20, 20], [30, 10] ] } |
| MultiPoint | MULTIPOINT (10 40, 40 30, 20 20, 30 10) | { “type”: “MultiPoint”, “coordinates”: [ [10, 40], [40, 30], [20, 20], [30, 10] ] } |
| MultiLineString | MULTILINESTRING ((10 10, 20 20, 10 40),(40 40, 30 30, 40 20, 30 10)) | { “type”: “MultiLineString”, “coordinates”: [ [[10, 10], [20, 20], [10, 40]], [[40, 40], [30, 30], [40, 20], [30, 10]] ] } |
| MultiPolygon | MULTIPOLYGON (((30 20, 45 40, 10 40, 30 20)),((15 5, 40 10, 10 20, 5 10, 15 5))) | { “type”: “MultiPolygon”, “coordinates”: [ [ [[30, 20], [45, 40], [10, 40], [30, 20]] ], [ [[15, 5], [40, 10], [10, 20], [5, 10], [15, 5]] ] ] } |
| MultiPolygon | MULTIPOLYGON (((40 40, 20 45, 45 30, 40 40)),((20 35, 10 30, 10 10, 30 5, 45 20, 20 35),(30 20, 20 15, 20 25, 30 20))) | { “type”: “MultiPolygon”, “coordinates”: [ [ [[40, 40], [20, 45], [45, 30], [40, 40]] ], [ [[20, 35], [10, 30], [10, 10], [30, 5], [45, 20], [20, 35]], [[30, 20], [20, 15], [20, 25], [30, 20]] ] ] } |
WKT与geojson的主要区别是wkt是单独用来表示空间点线面数据的，而geojson还可以用来表示空间数据和属性数据的集合，下面是shp面数据转geojson，其中还包含图层信息等，而wkt并不能表示这个。
{"type": "FeatureCollection","name": "a","crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:EPSG::3857" } },"features": [{