Writing GeoJSON from SharpMap, Part 1.5

Following up on my post a few months back about GeoJSON and SharpMap; here is the code to the converter as it stands so far. I have mentioned recently that things have been pretty busy at work so I have progressed on this more slowly than I had wished. I have yet to insert code to handle CRS but I thought it would be better to post something than nothing.

Basically, I just had to do some modifications to Morten’s original code for handling WKT. It was pretty straightforward owing mainly to the quality of Morten’s code. So here it is. Enjoy…

[sourcecode language=”csharp”]
// Copyright 2008 – William Dollins
// GeometryToGeoJson converter by William Dollins (bill@zekiah.com / www.zekiah.com)
//
// Date 2008-09-25
//
// This file is part of SharpMap.
// SharpMap is free software; you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// SharpMap is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public License
// along with SharpMap; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
//
//SOURCECODE IS MODIFIED FROM ANOTHER WORK AND IS ORIGINALLY BASED ON THE
//GeometryToWKT class of SharpMap which was in turn was based on GeoTools.NET (see below):
// Copyright 2005, 2006 – Morten Nielsen (www.iter.dk)
//
// This file is part of SharpMap.
// SharpMap is free software; you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// SharpMap is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public License
// along with SharpMap; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

// SOURCECODE IS MODIFIED FROM ANOTHER WORK AND IS ORIGINALLY BASED ON GeoTools.NET:
/*
* Copyright (C) 2002 Urban Science Applications, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/

using System;
using System.IO;
using System.Text;
using SharpMap.Geometries;

namespace SharpMap.Converters.GeoJson
{
///

/// Outputs the GeoJSON representation of a instance.
///

///
/// The GeoJSON representation of Geometry is designed to exchange geometry data in a form
/// sutiable for use my Javascript mapping clients that support GeoJSON, such as OpenLayers. /// Examples of GeoJSON representations of geometry objects can be found in the comments for individual
/// conversion routines. These examples are originally from the geojson.org site and were used for testing.
///
public class GeometryToGeoJson
{
#region Methods

///

/// Converts a Geometry to GeoJSON representation.
///

/// A Geometry to write. /// A GeoJSON geometry string (see the GeoJSON
/// Specification)
public static string Write(IGeometry geometry)
{
StringWriter sw = new StringWriter();
Write(geometry, sw);
return sw.ToString();
}

///

/// Converts a Geometry to its GeoJSON representation.
///

/// A geometry to process. /// Stream to write out the geometry’s text representation. ///
/// Geometry is written to the output stream as a GeoJSON geometry string (see the GeoJSON
/// Specification).
///
public static void Write(IGeometry geometry, StringWriter writer)
{
AppendGeometryTaggedText(geometry, writer);
}

///

/// Converts a Geometry to GeoJSON format, then Appends it to the writer.
///

/// The Geometry to process. /// The output stream to Append to. private static void AppendGeometryTaggedText(IGeometry geometry, StringWriter writer)
{
if (geometry == null)
throw new NullReferenceException(“Cannot write GeoJSON: geometry was null”); ;
if (geometry is Point)
{
Point point = geometry as Point;
AppendPointTaggedText(point, writer);
}
else if (geometry is LineString)
AppendLineStringTaggedText(geometry as LineString, writer);
else if (geometry is Polygon)
AppendPolygonTaggedText(geometry as Polygon, writer);
else if (geometry is MultiPoint)
AppendMultiPointTaggedText(geometry as MultiPoint, writer);
else if (geometry is MultiLineString)
AppendMultiLineStringTaggedText(geometry as MultiLineString, writer);
else if (geometry is MultiPolygon)
AppendMultiPolygonTaggedText(geometry as MultiPolygon, writer);
else if (geometry is GeometryCollection)
AppendGeometryCollectionTaggedText(geometry as GeometryCollection, writer);
else
throw new NotSupportedException(“Unsupported Geometry implementation:” + geometry.GetType().Name);
}

///

/// Converts a Coordinate to GeoJSON point format,
/// then Appends it to the writer.
///

/// the Coordinate to process /// the output writer to Append to private static void AppendPointTaggedText(Point coordinate, StringWriter writer)
{
writer.WriteLine(“{“);
writer.WriteLine(“”type”: “Point”,”);
writer.Write(“”coordinates”: “);
AppendPointText(coordinate, writer);
writer.WriteLine(“}”);
}

///

/// Converts a LineString to GeoJSON LineString format,
///

/// The LineString to process. /// The output stream writer to Append to. private static void AppendLineStringTaggedText(LineString lineString, StringWriter writer)
{
writer.WriteLine(“{“);
writer.WriteLine(“”type”: “LineString”,”);
writer.WriteLine(“”coordinates”: “);
AppendLineStringText(lineString, writer);
//writer.WriteLine(“]”);
writer.WriteLine(“}”);
}

///

/// Converts a Polygon to GeoJSON Polygon format,
/// then Appends it to the writer.
///

/// Th Polygon to process. /// The stream writer to Append to. private static void AppendPolygonTaggedText(Polygon polygon, StringWriter writer)
{
//{
// “type”: “Polygon”,
// “coordinates”: [
// [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ]
// ]
//}
// with holes (inner rings)
//{
// “type”: “Polygon”,
// “coordinates”: [
// [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ],
// [ [100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2] ]
// ]
//}

//{
//”type”: “Polygon”,
//”coordinates”:
//[ [[[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]], [[5, 5], [7, 5], [7, 7], [5, 7], [5, 5]]] ]
//}

writer.WriteLine(“{“);
writer.WriteLine(“”type”: “Polygon”,”);
writer.WriteLine(“”coordinates”: “);
//writer.Write(“[ “);
AppendPolygonText(polygon, writer);
//writer.WriteLine(” ]”);
//writer.WriteLine(“]”);
writer.WriteLine(“}”);
}

///

/// Converts a MultiPoint to <MultiPoint Tagged Text>
/// format, then Appends it to the writer.
///

/// The MultiPoint to process. /// The output writer to Append to. private static void AppendMultiPointTaggedText(MultiPoint multipoint, StringWriter writer)
{
//{
// “type”: “MultiPoint”,
// “coordinates”: [
// [100.0, 0.0], [101.0, 1.0]
// ]
//}
writer.WriteLine(“{“);
writer.WriteLine(“”type”: “MultiPoint”,”);
writer.WriteLine(“”coordinates”: “);
AppendMultiPointText(multipoint, writer);
writer.WriteLine(“}”);
}

///

/// Converts a MultiLineString to <MultiLineString Tagged
/// Text> format, then Appends it to the writer.
///

/// The MultiLineString to process /// The output stream writer to Append to. private static void AppendMultiLineStringTaggedText(MultiLineString multiLineString, StringWriter writer)
{
//{
// “type”: “MultiLineString”,
// “coordinates”: [
// [ [100.0, 0.0], [101.0, 1.0] ],
// [ [102.0, 2.0], [103.0, 3.0] ]
// ]
//}
writer.WriteLine(“{“);
writer.WriteLine(“”type”: “MultiLineString”,”);
writer.WriteLine(“”coordinates”: “);
AppendMultiLineStringText(multiLineString, writer);
writer.WriteLine(“}”);
}

///

/// Converts a MultiPolygon to <MultiPolygon Tagged
/// Text> format, then Appends it to the writer.
///

/// The MultiPolygon to process /// The output stream writer to Append to. private static void AppendMultiPolygonTaggedText(MultiPolygon multiPolygon, StringWriter writer)
{
//{
// “type”: “MultiPolygon”,
// “coordinates”: [
// [
// [ [102.0, 2.0], [103.0, 2.0], [103.0, 3.0], [102.0, 3.0], [102.0, 2.0] ]
// ],
// [
// [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ],
// [ [100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2] ]
// ]
// ]
//}
writer.WriteLine(“{“);
writer.WriteLine(“”type”: “MultiPolygon”,”);
writer.WriteLine(“”coordinates”: “);
AppendMultiPolygonText(multiPolygon, writer);
writer.WriteLine(“}”);

}

///

/// Converts a GeometryCollection to <GeometryCollection Tagged
/// Text> format, then Appends it to the writer.
///

/// The GeometryCollection to process /// The output stream writer to Append to. private static void AppendGeometryCollectionTaggedText(GeometryCollection geometryCollection, StringWriter writer)
{
//{
// “type”: “GeometryCollection”,
// “members”: [
// {
// “type”: “Point”,
// “coordinates”: [100.0, 0.0]
// },
// {
// “type”: “LineString”,
// “coordinates”: [
// [101.0, 0.0], [102.0, 1.0]
// ]
// }
// ]
//}
writer.WriteLine(“{“);
writer.WriteLine(“”type”: “GeometryCollection”,”);
writer.WriteLine(“”geometries”: “);
AppendGeometryCollectionText(geometryCollection, writer);
writer.WriteLine(“}”);
}

///

/// Converts a Coordinate to Point Text format then Appends it to the writer.
///

/// The Coordinate to process. /// The output stream writer to Append to. private static void AppendPointText(Point coordinate, StringWriter writer)
{
if (coordinate == null || coordinate.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
AppendCoordinate(coordinate, writer);
writer.Write(“]”);
}
}

///

/// Converts a Coordinate to <Point> format, then Appends
/// it to the writer.
///

/// The Coordinate to process. /// The output writer to Append to. private static void AppendCoordinate(Point coordinate, StringWriter writer)
{
for (uint i = 0; i < coordinate.NumOrdinates; i++) writer.Write(WriteNumber(coordinate[i]) + (i < coordinate.NumOrdinates - 1 ? ", " : "")); } ///

/// Converts a double to a string, not in scientific notation.
///

/// The double to convert. /// The double as a string, not in scientific notation.
private static string WriteNumber(double d)
{
return d.ToString(SharpMap.Map.numberFormat_EnUS);
}

///

/// Converts a LineString to <LineString Text> format, then
/// Appends it to the writer.
///

/// The LineString to process. /// The output stream to Append to. private static void AppendLineStringText(LineString lineString, StringWriter writer)
{

if (lineString == null || lineString.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
for (int i = 0; i < lineString.NumPoints; i++) { if (i > 0)
writer.Write(“, “);
writer.Write(“[“);
AppendCoordinate(lineString.Vertices[i], writer);
writer.Write(“]”);
}
writer.Write(“]”);
}
}

///

/// Converts a Polygon to <Polygon Text> format, then
/// Appends it to the writer.
///

/// The Polygon to process. /// private static void AppendPolygonText(Polygon polygon, StringWriter writer)
{
if (polygon == null || polygon.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
AppendLineStringText(polygon.ExteriorRing, writer);
for (int i = 0; i < polygon.InteriorRings.Count; i++) { writer.Write(", "); AppendLineStringText(polygon.InteriorRings[i], writer); } writer.Write("]"); } } ///

/// Converts a MultiPoint to <MultiPoint Text> format, then
/// Appends it to the writer.
///

/// The MultiPoint to process. /// The output stream writer to Append to. private static void AppendMultiPointText(MultiPoint multiPoint, StringWriter writer)
{

if (multiPoint == null || multiPoint.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
for (int i = 0; i < multiPoint.Points.Count; i++) { if (i > 0)
writer.Write(“, “);
writer.Write(“[“);
AppendCoordinate(multiPoint[i], writer);
writer.Write(“]”);
}
writer.Write(“]”);
}
}

///

/// Converts a MultiLineString to <MultiLineString Text>
/// format, then Appends it to the writer.
///

/// The MultiLineString to process. /// The output stream writer to Append to. private static void AppendMultiLineStringText(MultiLineString multiLineString, StringWriter writer)
{

if (multiLineString == null || multiLineString.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
for (int i = 0; i < multiLineString.LineStrings.Count; i++) { if (i > 0)
writer.Write(“, “);
AppendLineStringText(multiLineString[i], writer);
}
writer.Write(“]”);
}
}

///

/// Converts a MultiPolygon to <MultiPolygon Text> format, then Appends to it to the writer.
///

/// The MultiPolygon to process. /// The output stream to Append to. private static void AppendMultiPolygonText(MultiPolygon multiPolygon, StringWriter writer)
{

if (multiPolygon == null || multiPolygon.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
for (int i = 0; i < multiPolygon.Polygons.Count; i++) { if (i > 0)
writer.Write(“, “);
AppendPolygonText(multiPolygon[i], writer);
}
writer.Write(“]”);
}
}

///

/// Converts a GeometryCollection to <GeometryCollection Text > format, then Appends it to the writer.
///

/// The GeometryCollection to process. /// The output stream writer to Append to. private static void AppendGeometryCollectionText(GeometryCollection geometryCollection, StringWriter writer)
{
if (geometryCollection == null || geometryCollection.IsEmpty())
writer.Write(“EMPTY”);
else
{
writer.Write(“[“);
for (int i = 0; i < geometryCollection.Collection.Count; i++) { if (i > 0)
writer.Write(“, “);
AppendGeometryTaggedText(geometryCollection[i], writer);
}
writer.Write(“]”);
}
}
#endregion
}
}
[/sourcecode]