GHeat .Net

Introduction  

 A fast and free heat mapping tool. 

Background  

I had the need for a flexible and scalable heat mapping application. A quick Google search lead me to gheat. While playing with the application, I found it slow and not flexible enough to suit my needs. Their was no way to quickly and easily add points and the tile generating was slow. So I decided to attempt a port to C# and here I am now.

Using the code 

For simplicity i have already written all of the code to get anyone started right out of the box. 

UI (In VB)

I have made a session wrapper to store the points for each session. They are accessed through "SessionHandler.PointManager".

Dim pm As gheat.PointManager
pm = SessionHandler.PointManager
If pm.PointCount = 0 Then pm.LoadPointsFromFile("points.txt")

pm.AddPoint(New GMap.NET.PointLatLng(30.123866, -92.070673))

If you wish to have to points add via post I would suggest have a loop that adds each point. Below is an example: 

'Post data would look like x,yx,y
Dim lineSplit() As String
For Each line As String In Request("Address").Split("")
lineSplit = line.Split(",")
pm.AddPoint(New GMap.NET.PointLatLng(lineSplit(0), lineSplit(1)))
Next

Displaying the Tiles  

Dim image As System.Drawing.Bitmap
Dim stream As New System.IO.MemoryStream()
'Make sure nothing else is being sent
Response.Clear()
'Set the content type
Response.ContentType = "image/png"
'Get the tile image
image = gheat.GHeat.GetTile(SessionHandler.PointManager, Request("colorScheme"), CInt(Request("zoom")), CInt(Request("x")), CInt(Request("y")))

'Must save the image to a stream because png's need a stream that can seek back and forth.
image.Save(DirectCast(stream, System.IO.Stream), System.Drawing.Imaging.ImageFormat.Png)
stream.WriteTo(Response.OutputStream)
'Don't do anything else and send it to the requester
Response.Flush()

The Guts (In C#)

   Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        Dim baseDirectory As String = HttpRuntime.AppDomainAppPath

        gheat.Settings.BaseDirectory = baseDirectory + "__\etc\"
    End Sub

How Does It Work? (The Idea)

• Points are drawn onto tiles, the more points the more intense the color (Darker)
• Based on the intensity of the color (darkness) in the tile on a scale of 0-255 it is mapped to the color scheme which is 255 pixels high.
• Pixel by pixel is mapped and changed based on the color scheme
• The tile is trimmed due to it having to be larger to accommodate points on the edges of a tile
• Tile is sent out
• Everyone now smiles ;)

Bonus

        Dim pm As New gheat.PointManager()
        Dim g As Graphics
        Dim tempImage As System.Drawing.Bitmap
        Dim zoom As Integer = 4
        Dim startX As Integer = 2
        Dim startY As Integer = 5
        Dim maxX As Integer = startX + 10
        Dim maxY As Integer = startY + 10
        Dim canvasImage As New System.Drawing.Bitmap(maxX * 256 - (startX * 256), maxY * 256 - (startY * 256), System.Drawing.Imaging.PixelFormat.Format32bppArgb)

        gheat.Settings.BaseDirectory = "..\..\..\gheatWeb\__\etc\"

        g = Graphics.FromImage(canvasImage)

        pm.LoadPointsFromFile("..\..\..\points.txt")

        For x As Integer = startX To maxX
            For y As Integer = startY To maxY
                tempImage = gheat.GHeat.GetTile(pm, "classic", zoom, x, y)
                g.DrawImage(tempImage, New System.Drawing.PointF(x * 256 - (startX * 256), y * 256 - (startY * 256)))
            Next
        Next
        PictureBox1.Image = canvasImage

Thanks

Thanks to the original gheat project, I would of never had though of how to how to implement it with out the source code.

Image multiplication via a blending images project.

Mercator projection thanks to Great Maps. I would of included the source, but it was extremely large so i just compiled to a DLL and included it with the project. I did modify the source slightly to allow for weighted points. Maybe I will one day explain how that works.

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)