go - 如何用unmarshal解析gpx

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Can't decode XML with golang, always empty struct

(1个答案)


9个月前关闭。




我想解析一个GPX文件。我想获得以下信息:

文件中的所有点(trkpt)及其值:

经度

纬度

海拔

时间

为此，我编写了结构:

type gpx file{
    filepointer *os.file
    points []xmlPoints
}

type gpx struct {
    XMLName xml.Name `xml:"gpx"`
    trks trk `xml:"trk"`
}

type trk struct {
    XMLName xml.Name `xml:"trk"`
    trksegs []trkseg `xml:"trkseg"`
}

type trkseg struct {
    XMLName xml.Name   `xml:"trkseg"`
    points  []XMLPoint `xml:"trkpt"`
}

type XMLPoint struct {
    XMLName   xml.Name  `xml:"trkpt"`
    longitude float64   `xml:"lon,attr"`
    latitude  float64   `xml:"lat,attr"`
    elevation float64   `xml:"ele"`
    time      time.Time `xml:"time"`
}

我使用以下方法尝试获取这些值:

func (f *GPXFile) setPoints() {
    //Reads the GPXfile to get a slice of all Points and set them to f.points
    //read GPXFile
    file, _ := os.Open(f.filePointer.Name())
    fileByte, _ := ioutil.ReadAll(file)
    //get points
    var g gpx
    //should read points and puts them to &points, result empty
    err :=xml.Unmarshal(fileByte, &g)
    fmt.Print(err)
    //set points
    f.points = g.trks.trksegs[1].points
}

我的GPX文件如下所示:

<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" ...>
 <metadata>
  <time>2019-09-14T13:14:17.094Z</time>
 </metadata>

 <trk>
  <name>Cube – Sa., 14. Sep. 2019, 15:14</name>
  <trkseg>
  </trkseg>
  <trkseg>
   <trkpt lat="49.3547198000" lon="9.1508659200"><time>2019-09-14T13:14:00.000Z</time><extensions><gpxpx:PowerInWatts>120</gpxpx:PowerInWatts></extensions></trkpt>
   <trkpt lat="49.3546998700" lon="9.1509324100"><time>2019-09-14T13:14:10.003Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.9</gpxtpx:atemp></gpxtpx:TrackPointExtension><gpxpx:PowerInWatts>120</gpxpx:PowerInWatts></extensions></trkpt>
   <trkpt lat="49.3547521100" lon="9.1510961900"><time>2019-09-14T13:14:14.293Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.9</gpxtpx:atemp></gpxtpx:TrackPointExtension></extensions></trkpt>
   <trkpt lat="49.3547585400" lon="9.1513071400"><time>2019-09-14T13:14:20.310Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.9</gpxtpx:atemp></gpxtpx:TrackPointExtension></extensions></trkpt>
   <trkpt lat="49.3549890600" lon="9.1519649400"><ele>172.50</ele><time>2019-09-14T13:14:30.276Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.8</gpxtpx:atemp><gpxtpx:speed>5.54</gpxtpx:speed></gpxtpx:TrackPointExtension></extensions></trkpt>
   <trkpt lat="49.3550175500" lon="9.1520317100"><ele>172.23</ele><time>2019-09-14T13:14:32.291Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.8</gpxtpx:atemp><gpxtpx:speed>4.86</gpxtpx:speed></gpxtpx:TrackPointExtension></extensions></trkpt>
   <trkpt lat="49.3550991300" lon="9.1520247100"><ele>171.90</ele><time>2019-09-14T13:14:34.290Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.8</gpxtpx:atemp><gpxtpx:speed>4.54</gpxtpx:speed></gpxtpx:TrackPointExtension></extensions></trkpt>
   <trkpt lat="49.3551844700" lon="9.1519891400"><ele>171.33</ele><time>2019-09-14T13:14:36.275Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.8</gpxtpx:atemp><gpxtpx:speed>4.88</gpxtpx:speed></gpxtpx:TrackPointExtension></extensions></trkpt>
   <trkpt lat="49.3553612700" lon="9.1518673700"><ele>170.61</ele><time>2019-09-14T13:14:40.015Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:atemp>22.8</gpxtpx:atemp><gpxtpx:speed>5.55</gpxtpx:speed></gpxtpx:TrackPointExtension><gpxpx:PowerInWatts>121</gpxpx:PowerInWatts></extensions></trkpt>
  </trkseg>
 </trk>
</gpx>

问题是，从解组函数中，我得到了一个带有gpx的trk，但是trkseq是nil ...
如果我将trkseq中的trk设为单个trkseq而不是数组，则可以，但是要点为零。所以我想知道如何解析trkseq数组。从那里，我可以使用相同的方法来获取点数组。

最佳答案

在golang中编组/解组任何类型的编码/序列化数据时，解组的类型有时会作为interface{}类型传递。 (取消编组)代码将必须依赖reflect包来查找可用于将数据映射到的标签和字段。此代码只能使用(写入)的字段是导出字段(以大写字母开头的字段)。您的所有类型都具有未导出的字段和类型(如果可以，则为 private )。

只需更改以下内容:

type gpx struct {
    XMLName xml.Name `xml:"gpx"`
    trks    trk      `xml:"trk"`
}

至

type Gpx struct {
    XMLName xml.Name `xml:"gpx"`
    Trks    Trk      `xml:"trk"`
}

另外，在Golang中，惯例是使用所有大写字母作为首字母缩写(例如URL，而不是url或Url)，因此可以说，您需要:

type GPX struct {
    XMLName xml.Name `xml:"gpx"`
    TRKS    TRK      `xml:"trk"`
}