GeoJsonRenderer - Convert GeoJSON to images

Convert a GeoJSON string (or multiple GeoJSON strings) to PNG images.

This package currently contains 2 Visual Studio 2015 projects:

• GeoJsonRenderer, the class library that converts GeoJSON text to PNG images.
• GeoJsonConsole, a (very) simple command-line utility used to test GeoJsonRenderer during development.

Usage

Dependencies

In order to use GeoJsonRenderer in your projects, you will need to reference the following packages:

• Json.NET (https://www.nuget.org/packages/Newtonsoft.Json/)
• GeoJSON.Net (https://www.nuget.org/packages/GeoJSON.Net/)

Construction

Before using the renderer, it must be instantiated:

var Renderer = new GeoJsonRenderer(DefaultStyle);

The styling parameter is optional. The default style is a 2-pixel wide green line with no fill.

Styling

We can also change the default rendering style by instantiating a DrawingStyle object. The constructor takes the form new DrawingStyle(System.Drawing.Pen LinePen, System.Drawing.Brush FillBrush).

var R = new GeoJsonRenderer();
R.DefaultStyle = new DrawingStyle(new Pen(Color.Blue, 5.0f), new SolidBrush(Color.DarkBlue));

Note that the FillBrush property of a DrawingStyle is only applied to Polygon Geometries - LineStrings that completely enclose an area will not be treated as polygons unless they are defined as such.

Examples

Single GeoJSON string -> image file

Rendering a single GeoJSON string to a file is straightforward:

using(var R = new GeoJsonRenderer())
{
    var Reader = new StreamReader("testdata1.json");
    var Json = Reader.ReadToEnd();
    R.LoadGeoJson(Json);
    R.FitLayersToPage(640, 480);
    R.SaveImage(@"D:\TEMP\example1.png");
}

Multiple GeoJSON strings -> single image file

Rendering multiple strings to a file is not much more complex:

string[] Filenames = { "test-areas.json", "test-frame.json", "test-perimeter.json", "test-text.json" };
string[] Jsons = new string[Filenames.Length];
for (int i = 0; i < Filenames.Length; i++)
{
    var Reader = new StreamReader(Filenames[i]);
    string Text = Reader.ReadToEnd();
    Jsons[i] = Text;
}
using(var R = new GeoJsonRenderer())
{
    R.LoadGeoJson(Jsons);
    R.FitLayersToPage(640, 480);
    R.SaveImage(@"D:\TEMP\example2.png");
}

Already deserialised?

If your GeoJson objects are already deserialised (perhaps you're doing some other processing on them outside of just rendering to an image), you can add them directly:

FeatureCollection Features = JsonConvert.DeserializeObject<FeatureCollection>(json);
// (Your processing code here)
using(var R = new GeoJsonRenderer())
{
    R.Layers.Add(Features);
    R.FitLayersToPage(640, 480);
    R.SaveImage(@"D:\TEMP\example3.png");
}

Selective colour

GeoJsonRenderer raises an event before drawing each feature. We can handle that event to style features based on their properties. Here we want to highlight our ground floor:

static void main(string[] args)
{
    var reader = new StreamReader("testdata1.json");
    var Json = reader.ReadToEnd();
    using(var R = new GeoJsonRenderer())
    {
        R.DrawingFeature += R_DrawingFeature;
        R.LoadGeoJson(Json);
        R.FitLayersToPage(640, 480);
        R.SaveImage(@"D:\TEMP\example4.png");
    }    
}

private void R_DrawingFeature(object sender, DrawingFeatureEventArgs e)
{
    var BigBlueBorder = new DrawingStyle(new Pen(Color.Blue, 5.0f), new SolidBrush(Color.DarkBlue));
    if (e.Feature.Properties.ContainsKey("FLOOR") && e.Feature.Properties["FLOOR"].ToString() == "1")
    {
	    e.Style = BigBlueBorder;
    }
}

Adding a margin

The FitLayersToPage method accepts an optional parameter to add a margin (hence, keeping content from going right to the edge of the rendered image) as follows:

using(var R = new GeoJsonRenderer())
{
    R.LoadGeoJson(Json);
    R.FitLayersToPage(640, 480, 20);    // 20-pixel margin
    R.SaveImage(@"D:\TEMP\example5.png");
}

Splitting an image across multiple pages

The Paginate method can be used instead of FitLayersToPage. It accepts a threshold value for scaling. If the scale factor is below this threshold the canvas size is recursively doubled until the scale factor is above the threshold. In this circumstance, SaveImage(path) must be given a folder path not a file.

using(var R = new GeoJsonRenderer())
{
    R.LoadGeoJson(Json);
    R.Paginate(200, 100, 0.5, 20);  // 20-pixel margin on each page
    R.SaveImage(@"D:\TEMP\example6");
}

Future developments

Note: these ideas may or may not be implemented.

• Extend transform methods to be more useful for manipulating GeoJSON outside of a render-to-image context (arbitrary rotation centre etc.)
• More comprehensive testing, unit tests and so on.
• Make console app more fully-featured - currently configured through code, it'd be cool to see this made into a proper command-line tool rather than just the bare minimum to spit out a PNG file when I hit F5.