gumblex / leaflet.ChineseCRS

Leaflet plugin for using Chinese tile providers without offset.

leaflet.ChineseCRS

Leaflet plugin for using Chinese tile providers without offset.

This plugin uses the CRS appoach: Set the crs option of the map object, and your features with WGS84 coordinates (EPSG:4326) will be directly usable.

Usage

Add leaflet.ChineseCRS.js to your html/js project.

• L.ChineseCRS.wgs_gcj({lat, lng}): Convert coordinates from WGS84 (EPSG:4326) to GCJ02.
• L.ChineseCRS.wgs_bd({lat, lng}): Convert coordinates from WGS84 (EPSG:4326) to BD09.
• L.ChineseCRS.gcj_wgs({lat, lng}): Convert coordinates from GCJ02 to WGS84 (EPSG:4326).
• L.ChineseCRS.bd_wgs({lat, lng}): Convert coordinates from BD09 to WGS84 (EPSG:4326).
• L.ChineseCRS.Proj_GCJ02_3857: L.Projection object for Pseudo-Mercator (EPSG:3857) with GCJ02 coordinates.
• L.ChineseCRS.Proj_BaiduMercator: L.Projection object for Baidu Mercator with BD09 coordinates.
• L.ChineseCRS.CRS_GCJ02_3857: L.CRS object for Pseudo-Mercator (EPSG:3857) with GCJ02 coordinates.
• L.ChineseCRS.CRS_BaiduMercator: L.CRS object for Baidu Mercator with BD09 coordinates. This must be used with L.BaiduTileLayer.
• L.ChineseCRS.BaiduTileLayer: Tile layer for Baidu map.
• L.ChineseCRS.QQTileLayer: L.TileLayer, with {x4} and {y4} for QQ map's url.
• L.ChineseCRS.TimestampTileLayer: L.TileLayer, with {t} specifying current timestamp (milliseconds).
• L.ChineseCRS.getTileLayer(type, url, options):
  • type=baidu: return L.ChineseCRS.BaiduTileLayer object.
  • type=qq: return L.ChineseCRS.QQTileLayer object.
  • type=timestamp: return L.ChineseCRS.TimestampTileLayer object.
  • other: return L.TileLayer object.

Example: demo_gcj.html, demo_baidu.html.

Notes

The map projection chain:

• Proj_GCJ02_3857: WGS84(EPSG:4326) -> GCJ02 -> Pseudo-Mercator (EPSG:3857)
• Proj_BaiduMercator: WGS84(EPSG:4326) -> GCJ02 -> BD09 -> Baidu Mercator

Baidu Mercator is an (Ellipsoidal) Mercator projection with different ellipsoid parameters (Clarke 1866). This is guessed (using scipy) from Baidu's original approximate algorithm. (Inspired from leaflet-tileLayer-baidugaode)

PROJ string:

+proj=merc +a=6378206.4 +b=6356583.8 +lat_ts=0.0 +lon_0=0.0 +x_0=0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs

Acknowledgement

This work is based on PRCoords (GCJ02 and BD09 algorithms) and PROJ (Mercator algorithms).

See also: Leaflet.ChineseTmsProviders, leaflet-tileLayer-baidugaode (for provider urls), cntms (tile image reverse proxy, for GIS software).