JavaScript Topology Suite wrapper functions to validate GeoJSON features

featurevalidator.js

'use strict';
var jsts = require('jsts');
var geometryFactory = new jsts.geom.GeometryFactory();

var reader = new jsts.io.GeoJSONReader();

// Proper attribution: 
// adapted from http://stackoverflow.com/questions/25017463/google-maps-polygons-self-intersecting-detection
var findSelfIntersects = function(geoJSONPolygon) {
    var jstsGeometry  = reader.read(geoJSONPolygon.geometry);

    // if the geometry is aleady a simple linear ring, do not
    // try to find self intersection points.
    if (jstsGeometry) {
        var validator = new jsts.operation.IsSimpleOp(jstsGeometry);
        if (validator.isSimpleLinearGeometry(jstsGeometry)) {
            return;
        }

        var res = {};
        var graph = new jsts.geomgraph.GeometryGraph(0, jstsGeometry);
        var cat = new jsts.operation.valid.ConsistentAreaTester(graph);
        var r = cat.isNodeConsistentArea();
        if (!r) {
            res = cat.getInvalidPoint();
        }
        return res;
    }

};

function isSimpleGeoJSON(geoJSONPolygon){
    var jstsGeometry  = reader.read(geoJSONPolygon.geometry);

    if (jstsGeometry) {
        var validator = new jsts.operation.IsSimpleOp(jstsGeometry);
        return validator.isSimple();
    }
}

function isValidGeoJSON(geoJSONPolygon){
    var jstsGeometry  = reader.read(geoJSONPolygon.geometry);

    if (jstsGeometry) {
        var validator = new jsts.operation.valid.IsValidOp(jstsGeometry);
        return validator.isValid();
    }
}

var geojson = {
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": { name: 'My non-simple hourglass-shaped geometry' },
            "geometry": {
                "type": "Polygon",
                "coordinates": [
                    [
                        [
                            5.614013671875,
                            52.47608904123904
                        ],
                        [
                            6.35009765625,
                            52.93539665862318
                        ],
                        [
                            6.8939208984375,
                            52.13011607781287
                        ],
                        [
                            7.239990234375,
                            52.65639394198803
                        ],
                        [
                            5.614013671875,
                            52.47608904123904
                        ]
                    ]
                ]
            }
        },
        {
            "type": "Feature",
            "properties": { name: "my valid geometry"},
            "geometry": {
                "type": "Polygon",
                "coordinates": [
                    [
                        [
                            6.558837890625,
                            52.97180028087252
                        ],
                        [
                            6.536865234375,
                            53.1039189119836
                        ],
                        [
                            7.22625732421875,
                            53.08412692217884
                        ],
                        [
                            7.21527099609375,
                            52.91552722044141
                        ],
                        [
                            6.558837890625,
                            52.97180028087252
                        ]
                    ]
                ]
            }
        },
        {
            "type": "Feature",
            "properties": {
                "name": "My double hourglass shape"
            },
            "geometry": {
                "type": "Polygon",
                "coordinates": [
                    [
                        [
                            5.811767578125,
                            53.19451575316597
                        ],
                        [
                            5.6744384765625,
                            53.19451575316597
                        ],
                        [
                            5.67169189453125,
                            52.9751081817353
                        ],
                        [
                            5.809020996093749,
                            52.99990936843343
                        ],
                        [
                            5.9326171875,
                            53.21096737507053
                        ],
                        [
                            6.031494140625,
                            53.21425694166793
                        ],
                        [
                            6.185302734375,
                            52.985030365232305
                        ],
                        [
                            6.451721191406249,
                            52.96849212681396
                        ],
                        [
                            6.46270751953125,
                            53.199451902831555
                        ],
                        [
                            6.24298095703125,
                            53.207677555890015
                        ],
                        [
                            6.031494140625,
                            52.994950270267985
                        ],
                        [
                            5.9161376953125,
                            52.993297110978936
                        ],
                        [
                            5.811767578125,
                            53.19451575316597
                        ]
                    ]
                ]
            }
        },
        {
            "type": "Feature",
            "properties": {
                "name": "One point for good measure"
            },
            "geometry": {
                "type": "Point",
                "coordinates": [
                    6.611022949218749,
                    52.82766141733736
                ]
            }
        }
    ]
};

geojson.features.forEach(
    function validateEachFeature(feature, index, array) {
        console.log("Processing feature: " + index);
        var result = findSelfIntersects(feature);
        if (result) {
            var jstsPoint = geometryFactory.createPoint(result);
            var writer = new jsts.io.GeoJSONWriter();
            var geojsonResult = writer.write(jstsPoint);
            console.log("Self-intersection found at GeoJSON point: " + JSON.stringify(geojsonResult));
        } else {
            console.log("No self-intersection found");
        }

        console.log("Is a Simple Feature: " + isSimpleGeoJSON(feature));
        console.log("Is a valid feature: " + isValidGeoJSON(feature) + "\n");

    }
);