将自定义类型转换为类型 [][]float64

Question

使用 Golang，我想从数据库中获取这些跟踪点（纬度、经度）以生成如下所示的 GeoJSON 文件：

{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"LineString","coordinates":[[-122.271154,37.804348],[-122.272057,37.80295],[-122.272057,37.80295],[-122.278011,37.805288]]},"properties":null}]}

这是我的代码：

package main

import (
    "fmt"
    "log"
    "net/http"
    "time"

    "github.com/gorilla/mux"
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/mysql"
    geojson "github.com/paulmach/go.geojson"
    "github.com/shopspring/decimal"
)

var db *gorm.DB
var err error

type Trackpoint struct {
    Id        int             `json:"-"`
    Latitude  decimal.Decimal `json:"lat" sql:"type:decimal(10,8);"`
    Longitude decimal.Decimal `json:"long" sql:"type:decimal(11,8);"`
    Elevation uint
    Timestamp time.Time
}

func returnTrackpoints(w http.ResponseWriter, r *http.Request) {
    trackpoints := []Trackpoint{}
    db.Find(&trackpoints)
    coordinates := [][]float64{{-122.271154, 37.804348}, {-122.272057, 37.80295}, {-122.272057, 37.80295}, {-122.278011, 37.805288}}
    fc := geojson.NewFeatureCollection()
    fmt.Println(coordinates)
    fc.AddFeature(geojson.NewLineStringFeature(coordinates))
    rawJSON, err := fc.MarshalJSON()
    if err != nil {
        fmt.Println(err)
    }
    fmt.Fprintf(w, "%s", string(rawJSON))
}

func handleRequests() {
    log.Println("Starting development server at http://127.0.0.1:10000/")
    myRouter := mux.NewRouter().StrictSlash(true)
    myRouter.HandleFunc("/trackpoints", returnTrackpoints)
    log.Fatal(http.ListenAndServe(":10000", myRouter))
}

func main() {
    db, err = gorm.Open("mysql", "user:password&@tcp(127.0.0.1:3306)/database?charset=utf8&parseTime=True")

    if err != nil {
        log.Println("Connection Failed to Open")
    } else {
        log.Println("Connection Established")
    }

    db.AutoMigrate(&Trackpoint{})
    handleRequests()
}

如果我使用

fc.AddFeature(geojson.NewLineStringFeature(coordinates)) GeoJSON 输出看起来不错。

但我想使用数据库中的坐标，例如

fc.AddFeature(geojson.NewLineStringFeature(trackpoints))

使用我存储在数据库中的 GPS 数据，但出现错误

./main.go:33:44: cannot use trackpoint (type []Trackpoint) as type [][]float64 in argument to geojson.NewLineStringFeature

如何将 []Trackpoint 类型转换为 [][]float64？

Answer 1

1. 使用与跟踪点相同数量的元素制作切片
2. 循环遍历每个跟踪点
3. Convert decimal.Decimal types to float64
4. 在切片中设置 float64 坐标
5. 将新切片传递给fc.AddFeature

func returnTrackpoints(w http.ResponseWriter, r *http.Request) {
    trackpoints := []Trackpoint{}
    db.Find(&trackpoints)
    
    coordinates := make([][]float64, len(trackpoints))
    for i, trackpoint := range trackpoints {
        lat, _ := trackpoint.Latitude.Float64()
        long, _ := trackpoint.Longitude.Float64()
        coordinates[i] = []float64{
            lat,
            long,
        }
    }
    fc := geojson.NewFeatureCollection()
    fmt.Println(coordinates)
    fc.AddFeature(geojson.NewLineStringFeature(coordinates))
    rawJSON, err := fc.MarshalJSON()
    if err != nil {
        fmt.Println(err)
    }
    fmt.Fprintf(w, "%s", string(rawJSON))
}