使用XML包将TCX文件导入R

Question

我正在尝试使用XML包从TCX文件中导入GPS跑步数据到R中。这里是我拥有的一小部分数据样本（仅包含3个轨迹点而不是约900个）。

<?xml version="1.0" encoding="UTF-8"?>
<TrainingCenterDatabase xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.garmin.com/xmlschemas/TrainingCenterDatabase/v2">
<Activities>
    <Activity Sport="Running">
        <Id>2011-10-30T16:05:48Z</Id>
        <Lap StartTime="2011-10-30T16:05:48Z">
            <TotalTimeSeconds>3855.99</TotalTimeSeconds>
            <DistanceMeters>12498.8115</DistanceMeters>
            <MaximumSpeed>4.45662498</MaximumSpeed>
            <Calories>1011</Calories>
            <Intensity>Active</Intensity>
            <TriggerMethod>Manual</TriggerMethod>
            <Track>
                <Trackpoint>
                    <Time>2011-10-30T16:05:48Z</Time>
                    <Position>
                        <LatitudeDegrees>52.33613318</LatitudeDegrees>
                        <LongitudeDegrees>-1.58814317</LongitudeDegrees>
                    </Position>
                    <AltitudeMeters>77.5234375</AltitudeMeters>
                    <DistanceMeters>0.00000000</DistanceMeters>
                </Trackpoint>
                <Trackpoint>
                    <Time>2011-10-30T16:05:49Z</Time>
                    <Position>
                        <LatitudeDegrees>52.33614810</LatitudeDegrees>
                        <LongitudeDegrees>-1.58814283</LongitudeDegrees>
                    </Position>
                    <AltitudeMeters>77.5234375</AltitudeMeters>
                    <DistanceMeters>1.77584004</DistanceMeters>
                </Trackpoint>
                <Trackpoint>
                    <Time>2011-10-30T16:05:54Z</Time>
                    <Position>
                        <LatitudeDegrees>52.33627098</LatitudeDegrees>
                        <LongitudeDegrees>-1.58818323</LongitudeDegrees>
                    </Position>
                    <AltitudeMeters>76.0814209</AltitudeMeters>
                    <DistanceMeters>15.7694969</DistanceMeters>
                </Trackpoint>
            </Track>
        </Lap>
    </Activity>
</Activities>
</TrainingCenterDatabase>

我正在尝试使用以下代码读取轨迹点：

doc = xmlParse("filetest.tcx")
xmlToDataFrame(nodes = getNodeSet(doc, "//Trackpoint"))

然而，此方法失败，结果是一个空数据框。但是我发现，如果我删除

标签，则可以成功。

 xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.garmin.com/xmlschemas/TrainingCenterDatabase/v2"

从文件开头的TrainingCenterDatabase标签开始，使用以下数据，此导入将按预期正确运行。

<?xml version="1.0" encoding="UTF-8"?>
<TrainingCenterDatabase>
    <Activities>
        <Activity Sport="Running">
            <Id>2011-10-30T16:05:48Z</Id>
            <Lap StartTime="2011-10-30T16:05:48Z">
                <TotalTimeSeconds>3855.99</TotalTimeSeconds>
                <DistanceMeters>12498.8115</DistanceMeters>
                <MaximumSpeed>4.45662498</MaximumSpeed>
                <Calories>1011</Calories>
                <Intensity>Active</Intensity>
                <TriggerMethod>Manual</TriggerMethod>
                <Track>
                    <Trackpoint>
                        <Time>2011-10-30T16:05:48Z</Time>
                        <Position>
                            <LatitudeDegrees>52.33613318</LatitudeDegrees>
                            <LongitudeDegrees>-1.58814317</LongitudeDegrees>
                        </Position>
                        <AltitudeMeters>77.5234375</AltitudeMeters>
                        <DistanceMeters>0.00000000</DistanceMeters>
                    </Trackpoint>
                    <Trackpoint>
                        <Time>2011-10-30T16:05:49Z</Time>
                        <Position>
                            <LatitudeDegrees>52.33614810</LatitudeDegrees>
                            <LongitudeDegrees>-1.58814283</LongitudeDegrees>
                        </Position>
                        <AltitudeMeters>77.5234375</AltitudeMeters>
                        <DistanceMeters>1.77584004</DistanceMeters>
                    </Trackpoint>
                    <Trackpoint>
                        <Time>2011-10-30T16:05:54Z</Time>
                        <Position>
                            <LatitudeDegrees>52.33627098</LatitudeDegrees>
                            <LongitudeDegrees>-1.58818323</LongitudeDegrees>
                        </Position>
                        <AltitudeMeters>76.0814209</AltitudeMeters>
                        <DistanceMeters>15.7694969</DistanceMeters>
                    </Trackpoint>
                </Track>
            </Lap>
        </Activity>
    </Activities>
</TrainingCenterDatabase>

我得到了我想要的数据帧：（除了位置没有分成纬度和经度之外，但我预计我应该能够处理它，除非有人可以建议直接使用XPath更简单的方法来处理？）

> xmlToDataFrame(nodes = getNodeSet(doc, "//Trackpoint"))
                  Time               Position AltitudeMeters DistanceMeters
1 2011-10-30T16:05:48Z 52.33613318-1.58814317     77.5234375     0.00000000
2 2011-10-30T16:05:49Z 52.33614810-1.58814283     77.5234375     1.77584004
3 2011-10-30T16:05:54Z 52.33627098-1.58818323     76.0814209     15.7694969

显然，我不想手动从任何要导入的文件中删除它。我是否做错了什么（也许是XPath方面的问题？）导致这无法正常工作，或者有没有一种方法可以从XML数据中删除该部分？

非常感谢。

- Chris Wragg

Answer 1

这是一个命名空间问题。只需按照以下步骤进行操作。

xmlToDataFrame(nodes <- getNodeSet(doc, "//ns:Trackpoint", "ns"))

要直接获取由纬度和经度分割的位置，您可以执行以下操作

nodes <- getNodeSet(doc, "//ns:Trackpoint", "ns")
mydf  <- plyr::ldply(nodes, as.data.frame(xmlToList))
setNames(mydf, c('time', 'lat', 'long', 'alt', 'distance'))

它给出了什么

                  time         lat        long        alt   distance
1 2011-10-30T16:05:48Z 52.33613318 -1.58814317 77.5234375 0.00000000
2 2011-10-30T16:05:49Z 52.33614810 -1.58814283 77.5234375 1.77584004
3 2011-10-30T16:05:54Z 52.33627098 -1.58818323 76.0814209 15.7694969

- Ramnath