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web_mercator.go
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web_mercator.go
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package coordinate
import (
"fmt"
"math"
)
// WGS84ToWebMercator convert coordinate from WGS84 to web mercator
func WGS84ToWebMercator(src Coordinate) (Coordinate, error) {
var result Coordinate
if !src.Valid(WGS84) {
return result, fmt.Errorf("%s: [WGS84] %+v", InvalidParam, src)
}
result.X = src.X*WebMercatorHalfWidth/HalfRoundDegree + WebMercatorHalfWidth
result.Y = math.Log(math.Tan((QuarterRoundDegree+src.Y)*math.Pi/RoundDegree)) / DegreeToRadian
result.Y = result.Y * WebMercatorHalfWidth / HalfRoundDegree
result.Y = WebMercatorHalfWidth - result.Y
if !result.Valid(WebMercator) {
return result, fmt.Errorf("%s: [WebMercator] %+v", InvalidParam, src)
}
return result, nil
}
// WebMercatorToWGS84 convert from web mercator to WGS84
func WebMercatorToWGS84(src Coordinate) (Coordinate, error) {
var result Coordinate
if !src.Valid(WebMercator) {
return result, fmt.Errorf("%s: [WebMercator] %+v", InvalidParam, src)
}
result.Y = WebMercatorHalfWidth - src.Y
result.Y = result.Y * HalfRoundDegree / WebMercatorHalfWidth * DegreeToRadian
result.Y = math.Atan(math.Exp(result.Y))*RoundDegree/math.Pi - QuarterRoundDegree
result.X = (src.X - WebMercatorHalfWidth) * HalfRoundDegree / WebMercatorHalfWidth
if !result.Valid(WGS84) {
return result, fmt.Errorf("%s: [WGS84] %+v", InvalidParam, src)
}
return result, nil
}
// WGS84ToWebMercatorTile convert coordinate from WGS84 to web mercator tile number
func WGS84ToWebMercatorTile(src Coordinate, level int) (int, int, error) {
if !src.Valid(WGS84) {
return 0, 0, fmt.Errorf("%s: [WGS84] %+v", InvalidParam, src)
}
webMercator, err := WGS84ToWebMercator(src)
if err != nil {
return 0, 0, err
}
lineTileCount := 1 << level
levelTileWidth := WebMercatorWidth / float64(lineTileCount)
mapTileX, mapTileY := int(webMercator.X/levelTileWidth), int(webMercator.Y/levelTileWidth)
if mapTileX < 0 || mapTileY < 0 || mapTileX > lineTileCount || mapTileY > lineTileCount {
return 0, 0, fmt.Errorf("%s: [Web Mercator Tile] %+v", InvalidParam, src)
}
return mapTileX, mapTileY, nil
}