@giro3d/giro3d/src/utils/GeoJSONUtils.ts

A JS/WebGL framework for 3D geospatial data visualization

import { Feature } from 'ol';
import type { Geometry } from 'ol/geom';
import {
    GeometryCollection,
    LineString,
    MultiLineString,
    MultiPoint,
    MultiPolygon,
    Point,
    Polygon,
} from 'ol/geom';

/**
 * Given a simple GeoJSON Geometry object, returns the flat coordinates
 *
 * @param geojson - GeoJSON geometry object
 * @returns Flat coordinates
 */
function toFlatCoordinates(geojson: GeoJSON.Geometry): number[] {
    if (geojson.type === 'GeometryCollection') {
        throw new Error(`GeoJSON type '${geojson.type}' is not supported`);
    }
    return geojson.coordinates.flat(3);
}

/**
 * Creates a simple GeoJSON Geometry object from a list of 3D coordinates.
 *
 * @param flat3Coords - Coordinates
 * @param geometryType - Geometry type
 * @returns GeoJSON geometry object
 */
function fromFlat3Coordinates(
    flat3Coords: [number, number, number][],
    geometryType: GeoJSON.GeoJsonGeometryTypes,
): GeoJSON.Geometry {
    if (geometryType === 'GeometryCollection') {
        throw new Error(`GeoJSON type '${geometryType}' is not supported`);
    }

    switch (geometryType) {
        case 'Point':
            return {
                type: geometryType,
                coordinates: flat3Coords[0],
            };
        case 'LineString':
        case 'MultiPoint':
            return {
                type: geometryType,
                coordinates: flat3Coords,
            };
        case 'Polygon':
        case 'MultiLineString':
            return {
                type: geometryType,
                coordinates: [flat3Coords],
            };
        case 'MultiPolygon':
            return {
                type: geometryType,
                coordinates: [[flat3Coords]],
            };
        default:
            throw new Error(`GeoJSON type '${geometryType}' is not supported`);
    }
}

/**
 * Creates a simple GeoJSON Geometry object from a list of flat coordinates.
 *
 * Prefer `fromFlat3Coordinates` if possible (quicker, no object creation).
 *
 * @param flatCoords - Coordinates
 * @param geometryType - Geometry type
 * @returns GeoJSON geometry object
 */
function fromFlatCoordinates(
    flatCoords: number[],
    geometryType: GeoJSON.GeoJsonGeometryTypes,
): GeoJSON.Geometry {
    const coords = new Array(flatCoords.length / 3);
    for (let i = 0; i < flatCoords.length / 3; i += 1) {
        coords[i] = [flatCoords[i * 3 + 0], flatCoords[i * 3 + 1], flatCoords[i * 3 + 2]];
    }
    return fromFlat3Coordinates(coords, geometryType);
}

function getOpenLayersGeometry(geometry: GeoJSON.Geometry): Geometry {
    switch (geometry.type) {
        case 'Point':
            return new Point(geometry.coordinates);
        case 'MultiPoint':
            return new MultiPoint(geometry.coordinates);
        case 'LineString':
            return new LineString(geometry.coordinates);
        case 'MultiLineString':
            return new MultiLineString(geometry.coordinates);
        case 'Polygon':
            return new Polygon(geometry.coordinates);
        case 'MultiPolygon':
            return new MultiPolygon(geometry.coordinates);
        case 'GeometryCollection':
            return new GeometryCollection(geometry.geometries.map(getOpenLayersGeometry));
    }
}

function getOpenLayersFeature(feature: GeoJSON.Feature): Feature {
    return new Feature({
        geometry: getOpenLayersGeometry(feature.geometry),
    });
}

export default {
    toFlatCoordinates,
    fromFlat3Coordinates,
    fromFlatCoordinates,
    getOpenLayersFeature,
};