Updating xml file with powershell

Question

I'm trying to edit an XML file with Powershell. Specifically, a track in GPX format in which I want to correct the altitude coordinates of certain points, those corresponding to time after a certain moment (the time I changed the batteries to the GPS). This is the script with which I intend to do the update:

$filePath = "c:\users\g\documents\bat\PetroglifosV.gpx"
$xml = [xml] (Get-Content $filePath)
$nodes = $xml.SelectNodes("//trkpt")
# Write-Host "Tratando: " $nodes
foreach ($element in $nodes) {
   Write-Host "Tratando elemento: " $element.ele.InnerText
   if ($element.time.InnerText.Substring(11,5) -gt "08:48") { $element.ele.InnerText = 217 + $element.ele.InnerText }
   Write-Host "Tratado elemento: " $element.ele.InnerText
   }
$xml.Save("c:\users\g\documents\bat\petrotemp.txt")

And this is the XML file:

<?xml version="1.0" encoding="UTF-8"?>
<gpx creator="Wikiloc - https://www.wikiloc.com" version="1.1" xmlns="http://www.topografix.com/GPX/1/1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd">
  <metadata>
    <name>Wikiloc - Baiona a los petroglifos de Outeiro dos Lameiros</name>
    <author>
      <name>guigargi</name>
      <link href="https://www.wikiloc.com/wikiloc/user.do?id=657054">
        <text>guigargi on Wikiloc</text>
      </link>
    </author>
    <link href="https://www.wikiloc.com/hiking-trails/baiona-a-los-petroglifos-de-outeiro-dos-lameiros-26925951">
      <text>Baiona a los petroglifos de Outeiro dos Lameiros on Wikiloc</text>
    </link>
    <time>2018-07-23T09:55:48Z</time>
  </metadata>
  <trk>
    <name>Baiona a los petroglifos de Outeiro dos Lameiros</name>
    <cmt>
    </cmt>
    <desc>
    </desc>
    <trkseg>
      <trkpt lat="42.117677" lon="-8.847421">
        <ele>-12.431</ele>
        <time>2018-07-23T06:55:22Z</time>
      </trkpt>
      <trkpt lat="42.117649" lon="-8.847403">
        <ele>-12.461</ele>
        <time>2018-07-23T06:55:23Z</time>
      </trkpt>
      <trkpt lat="42.117661" lon="-8.847388">
        <ele>-12.407</ele>
        <time>2018-07-23T06:55:24Z</time>
      </trkpt>
      <trkpt lat="42.117687" lon="-8.847385">
        <ele>-12.408</ele>
        <time>2018-07-23T06:57:09Z</time>
      </trkpt>
      <trkpt lat="42.117593" lon="-8.847370">
        <ele>-12.435</ele>
        <time>2018-07-23T06:57:25Z</time>
      </trkpt>
      <trkpt lat="42.113513" lon="-8.838031">
        <ele>-184.594</ele>
        <time>2018-07-23T09:55:38Z</time>
      </trkpt>
      <trkpt lat="42.113517" lon="-8.838084">
        <ele>-184.520</ele>
        <time>2018-07-23T09:55:48Z</time>
      </trkpt>
    </trkseg>
  </trk>
</gpx>

It seems to me that it does not enter the FOR EACH loop, I guess because the $NODES array has nothing. The SAVE order seems work fine.

Can anyone help me. Thank you

GGG

Theo · Accepted Answer · 2022-08-19 09:09:56Z

1

You are comparing strings against strings, but what you need to do is compare TimeSpan objects against each other.

Try

# load the xml file. This way, you are ensured to get the file encoding correct
$xml = [System.Xml.XmlDocument]::new()
$xml.Load('c:\users\g\documents\bat\PetroglifosV.gpx')

# create a TimeSpan object to match the XML <time> elements against
$compareTime = [TimeSpan]::new(8,48,0)  # Hours, Minutes, Seconds

$nodes = $xml.DocumentElement.trk.trkseg.trkpt
foreach ($element in $nodes) {
   Write-Host "Tratando elemento: $($element.ele)"
   # the dates in the XML are given as UTC, so you probably want ToUniversalTime()
   $time = ([datetime]$element.time).ToUniversalTime().TimeOfDay  # --> convert into a TimeSpan object
   # compare the TimeSpan objects
   if ($time -gt $compareTime) { 
        $value = [double]$element.ele + 217
        $element.ele = "$value"
        Write-Host "Tratado elemento: $($element.ele)"
   }
}

$xml.Save('c:\users\g\documents\bat\petrotemp.xml')

answered Aug 19, 2022 at 9:09

Theo

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3 Comments

GGG Over a year ago

Perfect! It works very fine.

Theo Over a year ago

@GGG Thanks for the feedback. You may want to consider marking the question 'done' (see the tour), so others with a similar question may also benefit

GGG Over a year ago

I thank you again your comment. I hope to do things well next time.

jdweng · Accepted Answer · 2022-08-21 12:42:32Z

1

Here is similar solution

using assembly System 
using assembly System.Xml.Linq 

$inputFilename = "c:\temp\test.xml"
$outputFilename = "c:\temp\test1.xml"
$xDoc = [System.Xml.Linq.XDocument]::Load($inputFilename)
$root = [System.Xml.Linq.XElement]$xDoc.Root
$ns = [System.Xml.Linq.XNamespace]$root.GetDefaultNamespace()
$trkpts = $root.Descendants($ns + "trkpt")
#date in ZULU time.  Date is not important, only time of day
$timeOfDay = [DateTime]::Parse("1900-01-01T08:48:00Z").TimeOfDay

foreach($trkpt in $trkpts)
{
   $time = $trkpt.Element($ns + "time")
   $date = [DateTime]$time.Value
   if($date.TimeOfDay -gt $timeOfDay)
   {
      $ele = $trkpt.Element($ns + "ele")
      $oldValue = [decimal]$ele.Value
      $ele.Value = (217 + $oldValue)

   }
}
$xDoc.Save($outputFilename)

edited Aug 21, 2022 at 12:42

answered Aug 19, 2022 at 13:28

jdweng

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9 Comments

GGG Over a year ago

I suppose this solution could work as well but there are two issues that don't fit what I need: 1. Is not the time that must be modified when it is greater than 8:48 but the altitude (node "ele") 2. I don't see how I should do to save the modified data. I've tried xDoc.Save but it doesn't seem right. Anyway, thank you very much for your input.

jdweng Over a year ago

I update code and now works. To be consistent, your input time is in Zulu so the time of day you compare should also be in Zulu. So I changed 8:48 to 4:48. Converting to Universal time like Theo did is not consistent.

GGG Over a year ago

Now it works as expected, although I had to put 9:48 in the $timeOfDay variable (not 8:48 or 4:48). I can't explain why I needed to make that adjustment. I'm not qualified to judge the consistency of Theo's solution. But I can say that both solutions worked perfectly for me. Thanks again. GGG

jdweng Over a year ago

Try changing year to 2000. Day Light Savings Time probably didn't exist in 1900.

GGG Over a year ago

I've tried year to 2000-01-01 with the same results: I need to set time to 09:48. If I set date/time to 2018-07-23T08:48:00Z it works fine.

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