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annotate pkg/imports/polygon.go @ 972:17a03a84b0e8

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Split out polygon code out of sounding result importer source file.
author Sascha L. Teichmann <sascha.teichmann@intevation.de>
date Thu, 18 Oct 2018 12:22:08 +0200
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children a244b18cb916
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972
17a03a84b0e8 Split out polygon code out of sounding result importer source file.
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1 package imports
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2
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3 import (
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4 "bytes"
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5 "encoding/binary"
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6 "fmt"
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7 "math"
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8
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9 shp "github.com/jonas-p/go-shp"
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10 )
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11
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12 type (
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13 Point struct {
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14 X float64
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15 Y float64
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16 }
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17 LineString []Point
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18 Polygon []LineString
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19 )
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20
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21 const (
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22 wkbNDR byte = 1
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23 wkbPolygon uint32 = 3
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24 )
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26 func shapeToPolygon(s shp.Shape) (Polygon, error) {
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27 switch p := s.(type) {
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28 case *shp.Polygon:
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29 return toPolygon(p.NumParts, p.Parts, p.Points), nil
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30 case *shp.PolygonZ:
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31 return toPolygon(p.NumParts, p.Parts, p.Points), nil
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32 case *shp.PolygonM:
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33 return toPolygon(p.NumParts, p.Parts, p.Points), nil
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34 }
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35 return nil, fmt.Errorf("Unsupported shape type %T", s)
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36 }
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37
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38 func toPolygon(numParts int32, parts []int32, points []shp.Point) Polygon {
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39 out := make(Polygon, numParts)
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40 pos := 0
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41 for i := range out {
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42 ps := parts[i]
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43 line := make(LineString, ps)
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44 for j := int32(0); j < ps; j, pos = j+1, pos+1 {
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45 p := &points[pos]
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46 line[j] = Point{p.X, p.Y}
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47 }
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48 out[i] = line
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49 }
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50 return out
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51 }
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52
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53 func (p Polygon) AsWBK() []byte {
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54 if p == nil {
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55 return nil
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56 }
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57 // pre-calculate size to avoid reallocations.
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58 size := 1 + 4 + 4
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59 for _, ring := range p {
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60 size += 4 + len(ring)*2*8
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61 }
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62
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63 buf := bytes.NewBuffer(make([]byte, 0, size))
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64
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65 binary.Write(buf, binary.LittleEndian, wkbNDR)
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66 binary.Write(buf, binary.LittleEndian, wkbPolygon)
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67 binary.Write(buf, binary.LittleEndian, uint32(len(p)))
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68
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69 for _, ring := range p {
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70 binary.Write(buf, binary.LittleEndian, uint32(len(ring)))
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71 for _, v := range ring {
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72 binary.Write(buf, binary.LittleEndian, math.Float64bits(v.X))
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73 binary.Write(buf, binary.LittleEndian, math.Float64bits(v.Y))
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74 }
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75 }
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76
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77 return buf.Bytes()
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78 }