Extract Polygon name and coordinates from a KML using VB.NET

Question

I've been trying all day to write some code that will read the data from a kml containing a google earth polygon and extract the name and the coordinates and store everything as latitudes and longitudes. I already made a user form that allows the user to browse for the kml and then run the extraction code. Unfortunately the extraction doesn't work. I'm very new to VB but I did take three semesters of C++ in college, it's been close to a year since then though. Here's what I have but I understand that I could also be completely wrong..

Function X(InputFile As String, Text As String)

    Dim textReader As New Xml.XmlTextReader(InputFile)
    Dim lastElementName As String = ""
    While textReader.Read()
        Select Case textReader.NodeType
            Case Xml.XmlNodeType.Element
                lastElementName = textReader.Name
            Case Xml.XmlNodeType.Text
                MsgBox(lastElementName & ": " & textReader.Value)
        End Select
        Console.WriteLine()
    End While

Basic KML Example:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <Placemark>
    <name>The Pentagon</name>
    <Polygon>
      <tessellate>1</tessellate>
      <outerBoundaryIs>
        <LinearRing>
      <coordinates>
        -77.05668055019126,38.87154239798456
        -77.05542625960818,38.87167890344077
        -77.05485125901024,38.87076535397792
        -77.05577677433152,38.87008686581446
        -77.05691162017543,38.87054446963351
        -77.05668055019126,38.87154239798456
      </coordinates>
    </LinearRing>
   </outerBoundaryIs>
    </Polygon>
  </Placemark>
</kml>

Answer 1

As far as I can tell, you have the following subproblems:

1. Parse the XML and extract the name and the coordinates.

2. Split the coordinates into some data structure.

---

For step 1, VB's LINQ to XML is the easiest way. The following working code example should help you get started:

Imports <xmlns="http://www.opengis.net/kml/2.2">

Module Module1
    Sub Main()
        Dim xdata = New XDocument( _
            <kml xmlns="http://www.opengis.net/kml/2.2">
                <Placemark>
                    <name>The Pentagon</name>
                    <Polygon>
                        <tessellate>1</tessellate>
                        <outerBoundaryIs>
                            <LinearRing>
                                <coordinates>
                                -77.05668055019126,38.87154239798456
                                -77.05542625960818,38.87167890344077
                                -77.05485125901024,38.87076535397792
                                -77.05577677433152,38.87008686581446
                                -77.05691162017543,38.87054446963351
                                -77.05668055019126,38.87154239798456
                                </coordinates>
                            </LinearRing>
                        </outerBoundaryIs>
                    </Polygon>
                </Placemark>
            </kml>)

        For Each p In xdata.Root.<Placemark>
            Console.WriteLine("Name: " & p.<name>.Value)

            For Each c In p...<coordinates>
                Console.WriteLine("Coordinates: " & c.Value)
            Next
        Next

        Console.ReadLine()
    End Sub
End Module

Some remarks:

• If you want to read the data from a file, use XDocument.Load instead of New XDocument.
• The Imports statement at the top of the file is important, it must match the xmlns declaration at the start of the KML file.

Step 2 is left as an exercise, but String.Split (first on line breaks, then on the comma) and String.Trim (to remove the whitespace) should let you solve this easily.