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99 lines
3.2 KiB
99 lines
3.2 KiB
// Copyright (c) 2017 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package geo
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import (
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"fmt"
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"math"
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"strconv"
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"strings"
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)
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type distanceUnit struct {
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conv float64
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suffixes []string
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}
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var inch = distanceUnit{0.0254, []string{"in", "inch"}}
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var yard = distanceUnit{0.9144, []string{"yd", "yards"}}
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var feet = distanceUnit{0.3048, []string{"ft", "feet"}}
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var kilom = distanceUnit{1000, []string{"km", "kilometers"}}
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var nauticalm = distanceUnit{1852.0, []string{"nm", "nauticalmiles"}}
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var millim = distanceUnit{0.001, []string{"mm", "millimeters"}}
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var centim = distanceUnit{0.01, []string{"cm", "centimeters"}}
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var miles = distanceUnit{1609.344, []string{"mi", "miles"}}
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var meters = distanceUnit{1, []string{"m", "meters"}}
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var distanceUnits = []*distanceUnit{
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&inch, &yard, &feet, &kilom, &nauticalm, &millim, ¢im, &miles, &meters,
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}
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// ParseDistance attempts to parse a distance string and return distance in
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// meters. Example formats supported:
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// "5in" "5inch" "7yd" "7yards" "9ft" "9feet" "11km" "11kilometers"
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// "3nm" "3nauticalmiles" "13mm" "13millimeters" "15cm" "15centimeters"
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// "17mi" "17miles" "19m" "19meters"
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// If the unit cannot be determined, the entire string is parsed and the
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// unit of meters is assumed.
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// If the number portion cannot be parsed, 0 and the parse error are returned.
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func ParseDistance(d string) (float64, error) {
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for _, unit := range distanceUnits {
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for _, unitSuffix := range unit.suffixes {
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if strings.HasSuffix(d, unitSuffix) {
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parsedNum, err := strconv.ParseFloat(d[0:len(d)-len(unitSuffix)], 64)
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if err != nil {
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return 0, err
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}
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return parsedNum * unit.conv, nil
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}
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}
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}
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// no unit matched, try assuming meters?
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parsedNum, err := strconv.ParseFloat(d, 64)
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if err != nil {
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return 0, err
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}
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return parsedNum, nil
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}
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// ParseDistanceUnit attempts to parse a distance unit and return the
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// multiplier for converting this to meters. If the unit cannot be parsed
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// then 0 and the error message is returned.
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func ParseDistanceUnit(u string) (float64, error) {
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for _, unit := range distanceUnits {
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for _, unitSuffix := range unit.suffixes {
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if u == unitSuffix {
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return unit.conv, nil
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}
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}
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}
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return 0, fmt.Errorf("unknown distance unit: %s", u)
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}
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// Haversin computes the distance between two points.
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// This implemenation uses the sloppy math implemenations which trade off
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// accuracy for performance. The distance returned is in kilometers.
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func Haversin(lon1, lat1, lon2, lat2 float64) float64 {
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x1 := lat1 * degreesToRadian
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x2 := lat2 * degreesToRadian
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h1 := 1 - cos(x1-x2)
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h2 := 1 - cos((lon1-lon2)*degreesToRadian)
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h := (h1 + cos(x1)*cos(x2)*h2) / 2
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avgLat := (x1 + x2) / 2
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diameter := earthDiameter(avgLat)
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return diameter * asin(math.Min(1, math.Sqrt(h)))
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}
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