GeoHashingResearch

main.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"strconv"
	"strings"

	"github.com/mmcloughlin/geohash"
)

// ParseFloatsFile loads any number of float64 values from text file, returning
// N x M_i [][]float64 slice, where N is number of lines and M_i — number of floats
// per singline line in the input file.
func ParseFloatsFile(fileNamePtr *string) ([][]float64, error) {
	var err error
	var floats [][]float64
	var lineFloats []float64
	// Open the file
	txtFile, err := os.Open(*fileNamePtr)
	if err != nil {
		return floats, err
	}

	// Parse the file
	r := bufio.NewReader(txtFile)

	// Iterate through the records
	for {
		// Read each line from file
		lineString, err := r.ReadString('\n')
		if err == io.EOF {
			break
		}
		if err != nil {
			return floats, err
		}
		linePoints := strings.Split(lineString, ";")
		lineFloats = []float64{}
		for _, entry := range linePoints {
			if len(entry) > 3 {
				trimmededEntry := strings.Trim(entry, "\n\r")
				splitLineFloats := strings.Split(trimmededEntry, ",")
				for _, valueAsString := range splitLineFloats {
					value, conversionError := strconv.ParseFloat(valueAsString, 64)
					if conversionError != nil {
						return floats, err
					}
					lineFloats = append(lineFloats, value)
				}
			}
		}
		floats = append(floats, lineFloats)
	}
	return floats, err
}

func testPrecision(coordsSlice [][2]float64, precision uint) int {
	var hashesCount map[uint64]int
	var hash uint64
	var ok bool

	hashesCount = make(map[uint64]int)

	for _, coordsPair := range coordsSlice {
		lat := coordsPair[0]
		long := coordsPair[1]
		hash = geohash.EncodeIntWithPrecision(lat, long, precision)
		_, ok = hashesCount[hash]
		if !ok {
			hashesCount[hash] = 1
		} else {
			hashesCount[hash]++
		}
	}
	return len(hashesCount)
}

func main() {
	var testValues [][2]float64
	testFloatsFile := flag.String("f", "./test_values.txt", "Points to geohash. One pair separated with commas per line. Example: 25.2,22.2")
	flag.Parse()
	testData, err := ParseFloatsFile(testFloatsFile)
	if err != nil {
		log.Fatalln("Error parsing, ", err)
	}
	for _, lineSlice := range testData {
		lat := lineSlice[0]
		long := lineSlice[1]
		testValues = append(testValues, [2]float64{lat, long})
	}
	fmt.Println("Precision\t# of different hashes\t# of points")
	totalCount := len(testValues)
	for i := 1; i < 65; i++ {
		fmt.Printf("%d\t%d\t%d\n", i, testPrecision(testValues, uint(i)), totalCount)
	}
}

test_values.txt

59.992309,30.113443
60.096533,30.273693
59.960924,30.539487
59.866867,30.589095
59.726488,30.373295
59.848639,30.089489
59.944573,30.331566