Meziantou.Framework.Geo 1.0.2

Meziantou.Framework.Geo

Reads and writes maps in GeoJSON, TopoJSON, Shapefile, KML, KMZ, GPX, WKT, WKB, encoded polylines and FlatGeobuf, with features, geometries, geometry operations (repair, clip, simplify, union, intersection, difference, distance, buffer, convex hull) and map projections. No dependency outside .NET.

Usage

The types are in the Meziantou.Framework.Geo namespace. Every format is a static class with Read/Parse and Write/Format methods, which return and take a GeoFeatureCollection.

GeoFeatureCollection countries;
using (var stream = File.OpenRead("countries.geojson"))
{
    countries = GeoJson.Read(stream);
}

// A JSON number is a double, and a string is a string
var large = countries.Where(country => (double)country.Properties["population"]! > 50).ToList();
Assert.Equal("France", Assert.Single(large).Properties["name"]);

using (var stream = File.Create("large-countries.geojson"))
{
    GeoJson.Write(new GeoFeatureCollection(large), stream, new GeoJsonWriterOptions { Indented = true });
}

Compute distances and test whether a position is inside an area:

// A square with a square hole
var polygon = new GeoPolygon(
[
    [new(0, 0), new(10, 0), new(10, 10), new(0, 10), new(0, 0)],
    [new(4, 4), new(6, 4), new(6, 6), new(4, 6), new(4, 4)],
]);

Assert.True(polygon.Contains(new GeoPosition(Longitude: 2, Latitude: 2)));
Assert.False(polygon.Contains(new GeoPosition(Longitude: 5, Latitude: 5))); // in the hole
Assert.False(polygon.Contains(new GeoPosition(Longitude: 12, Latitude: 5)));

Project positions onto a plane to draw a map:

var projection = new MercatorProjection();

// The point is in radii of the Earth, with y increasing to the north
var (x, y) = projection.Project(new GeoPosition(Longitude: 2.35, Latitude: 48.86));

// Scale and translate it to draw a map of 512 by 512 pixels, as the tiles of web maps
var pixelX = 256 + (x * 256 / Math.PI);
var pixelY = 256 - (y * 256 / Math.PI);
Assert.Equal(259.34, pixelX, 0.01);
Assert.Equal(176.14, pixelY, 0.01);

// Invert converts a point back to a position
var position = projection.Invert(x, y);
Assert.Equal(48.86, position!.Value.Latitude, 1e-9);

Formats

The positions are longitudes and latitudes in degrees (WGS 84). CoordinateReferenceSystem converts data in Web Mercator, UTM, Lambert 93 and other transverse Mercator, Lambert conformal conic and Mercator projections to them, from an EPSG code (the SRID of EWKT and EWKB) or the WKT of a .prj file.