背景

    平時我們可能有比較大量的點資料要展示又不想預處理，線上瀏覽資料請求時間控制在3s左右。

準備

    軟體環境:PostGIS,資料是3578998條點資料。

環境

    八核處理器(Intel(R)Core(TM) i7-10750H CPU @2.60GHz 2.59GHZ),RAM 16.0 GB,硬碟SSD

原理

    聚合原理參考我之前的文章千萬資料展示-向量切片點聚合。
比較重要的是要進行pg資料庫配置修改,參考阿里的配置項,調整過程中要先備份好配置檔案，可以修改完一兩個配置就重啟資料庫，這樣就避免全部修改完不能啟動的尷尬局面。

--示例1
 SELECT ST_AsMVT(vt,'points',256,'geo') tile 
FROM (select ST_SetSRID( ST_Point( ST_X(a.geo),ST_Y(a.geo)), 4326) geo from (
	SELECT ST_AsMVTGeom(w.geom,Box2D(TileBBox(10,176,409,4326)),256,0,true) AS geo 
FROM  public.capnt w  where TileBBox(10,176,409,4326)&&geom) a
group by ST_X(a.geo),ST![](https://p1-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/644f045b96e34fe6b4d456c6eb8e8d13~tplv-k3u1fbpfcp-zoom-1.image)_Y(a.geo)  ) AS  vt					
 

實戰

    寫個簡單的查詢服務，當級別在8-11級別可以使用聚合減少資料量，當級別大於11級直接查出就可以

package main
import 
(   
    _ "github.com/lib/pq"
	"database/sql"
	"github.com/julienschmidt/httprouter"
	"time"
    "log"
    "errors"
	"fmt"
    "net/http"
	"strconv"
	"bytes"
    "compress/gzip"
)
func FloatToString(input_num float64) string {
    return strconv.FormatFloat(input_num, 'f', 6, 64)
}

func gZipData(data []byte) (compressedData []byte, 
	err error) {
	var b bytes.Buffer
	gz := gzip.NewWriter(&b)

	_, err = gz.Write(data)
	if err != nil {
		return
	}

	if err = gz.Flush(); err != nil {
		return
	}

	if err = gz.Close(); err != nil {
		return
	}
	compressedData =b.Bytes()
	return
}

func check(e error) {
    if e != nil {
        log.Fatal(e)
    }
}

type Tile struct {
	X, Y, Z int
}
// ZMax is the maximum Z coordinate for a tile as well as quadkey level
const ZMax = 23
func Tile2Quadkey(t Tile) string {
	//bytes.Buffer was bottleneck
	z := t.Z
	var qk [ZMax]byte
	for i := z; i > 0; i-- {
		q := 0
		m := 1 << uint(i-1)
		if (t.X & m) != 0 {
			q++
		}
		if (t.Y & m) != 0 {
			q += 2
		}
		var d byte
		switch q {
		case 0:
			d = '0'
		case 1:
			d = '1'
		case 2:
			d = '2'
		case 3:
			d = '3'
		default:
			panic("Invalid tile.Quadkey()")
		}
		qk[z-i] = d
	}
	return string(qk[:z])
}
func Quad2Tile(qk string) (tile Tile, err error) {
	tile.Z = len(qk)
	for i := tile.Z; i > 0; i-- {
		m := 1 << uint(i-1)
		c := len(qk) - i
		q := qk[c]
		switch q {
		case '0':
		case '1':
			tile.X |= m
		case '2':
			tile.Y |= m
		case '3':
			tile.X |= m
			tile.Y |= m
		default:
			err = errors.New("Invalid Quadkey " + qk)
			tile = Tile{} // zero tile
			return
		}
	}
	return
}
func createTile(w http.ResponseWriter, r *http.Request, p httprouter.Params){
	//start := time.Now() 
	header := w.Header()
	if origin := r.Header.Get("Origin"); origin != "" {
		header.Set("Access-Control-Allow-Methods", r.Header.Get("Allow"))
		header.Set("Access-Control-Allow-Origin", "*")
	}
	header.Set("Content-Type", "application/x-protobuf")
	header.Add("Content-Encoding", "gzip")
	header.Add("Accept-Encoding", "gzip")
	xs:=p.ByName("x")
	ys:=p.ByName("y")
	zs:=p.ByName("z")
	z,errz := strconv.Atoi(zs)
	check(errz) 

	if (z>min){
				
		var sql string
		bbox:=zs+","+xs+","+ys
		if (z>min&&z<max){
			sql="SELECT ST_AsMVT(vt,'points',256,'geo') tile FROM (select ST_SetSRID( ST_Point( ST_X(a.geo),ST_Y(a.geo)), 4326) geo from (	SELECT ST_AsMVTGeom(w.geom,Box2D(TileBBox("+bbox+",4326)),256,0,true) AS geo FROM  "+table+" w  where TileBBox("+bbox+",4326)&&geom) a group by ST_X(a.geo),ST_Y(a.geo)  ) AS  vt"	

		}else{
			sql="SELECT ST_AsMVT(tile,'points',4096,'geom') tile  FROM (SELECT ST_AsMVTGeom(w.geom,Box2D(TileBBox("+bbox+",4326)),4096, 0, true) AS geom FROM "+table+" w where TileBBox("+bbox+",4326)&&w.geom ) AS  tile "
						
		}
		//fmt.Println(sql)
		var tile []byte				
		rows:= db.QueryRow(sql)
		err := rows.Scan(&tile)
		if err != nil {
		log.Fatal(err)
			http.Error(w, "Invalid tile url", 400)
			return
		}
		size := cap(tile)
		if size== 0 {			
			http.Error(w, "Invalid tile url", 400)
			return
		}
		compressedData, Err := gZipData(tile)
		if Err != nil {
			log.Fatal(Err)
			http.Error(w, "Invalid tile url", 400)
			return
		}else{

			w.Write(compressedData)
		}

	}else{

		http.Error(w, "Invalid tile url", 400)
		return
	}

}
var db *sql.DB
var err error
var table string
var min int=7
var	max int=12
var tileBase string
func main(){
	start := time.Now() 
	table="public.\"point_grid\""
	mux :=  httprouter.New()
	tileBase = "/tiles/:z/:x/:y"
	connStr := "dbname=postgis_30_sample user=postgres password=123456 host=localhost port=5432  sslmode=disable"
	db, err = sql.Open("postgres", connStr)
	if err != nil {
		panic(err)
	}
	defer db.Close()
	err = db.Ping()
	if err != nil {
		panic(err)
	}
	db.SetMaxOpenConns(8) 
	db.SetMaxIdleConns(8)
	elapsed := time.Since(start)
	fmt.Println("min max ", min,max)
	fmt.Println("啟動耗時: ", elapsed)
	mux.GET(tileBase, createTile) 
	log.Fatal(http.ListenAndServe(":8081", mux))
}
 

參考資料：

https://developer.aliyun.com/article/700363