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>

Welcome to SO! Unfortunately, as it currently stands, your question is too broad. I doubt that many readers here are familiar with the details of the KML format. Maybe it would help if you could provide a short, minimal example of a KML file that you want to parse (reduced to the relevant parts). In general, I think that [VB LINQ to XML](http://stackoverflow.com/a/1066418/87698) will help you with your problem, but it's hard to tell without details. — Heinzi, Jun 11 '14 at 20:36

score 2 · Accepted Answer · answered Jun 14 '14 at 16:23

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

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

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

1 Answers1