@seasketch/geoprocessing/dist/src/toolbox/clip.js

Geoprocessing and reporting framework for SeaSketch 2.0

import polygonClipping from "polygon-clipping";
import { multiPolygon, polygon, geomEach, getGeom, featureCollection, } from "@turf/turf";
import { ValidationError } from "../types/index.js";
import { chunk } from "../helpers/chunk.js";
/**
 * Performs one of 4 different clip operations on features
 * @param features - FeatureCollection of Polygons or MultiPolygons.  First feature is the subject, the rest are the clippers
 * @param operation - one of "union", "intersection", "xor", "difference"
 * @param options - optional properties to set on the resulting feature
 * @returns clipped Feature of Polygon or MultiPolygon
 */
export function clip(features, operation, options = {}) {
    if (!features || !features.features || features.features.length === 0)
        throw new ValidationError("Missing or empty features for clip");
    const coords = [];
    geomEach(features, (geom) => {
        coords.push(geom.coordinates);
    });
    //@ts-expect-error type mismatch
    const clipped = polygonClipping[operation](coords[0], ...coords.slice(1));
    if (clipped.length === 0)
        return null;
    if (clipped.length === 1)
        return polygon(clipped[0], options.properties);
    return multiPolygon(clipped, options.properties);
}
/**
 * Performs clip after first merging features2 coords into a single multipolygon.
 * Avoids errors in underlying clipping library when too many features in features2
 * @param feature1 polygon or multipolygon to clip
 * @param features2 collection of polygons or multipolygons to clip feature1 against
 * @param operation one of "union", "intersection", "xor", "difference"
 * @param options.properties properties to set on the resulting feature
 * @returns polygon or multipolygon feature result from clip operation, if no overlap then returns null
 */
export function clipMultiMerge(feature1, features2, operation, options = {}) {
    if (!feature1 ||
        !features2 ||
        !features2.features ||
        features2.features.length === 0)
        throw new ValidationError("Missing or empty features for clip");
    const geom1 = getGeom(feature1);
    // Combine features2 into one multipoly coordinate array so that it is operated on in one go
    const coords2 = (() => {
        return features2.features.reduce((acc, poly) => {
            if (poly.geometry.type === "Polygon") {
                return [...acc, poly.geometry.coordinates];
            }
            else {
                return [...acc, ...poly.geometry.coordinates];
            }
        }, []);
    })();
    const result = polygonClipping[operation](geom1.coordinates, coords2);
    if (result.length === 0)
        return null;
    if (result.length === 1)
        return polygon(result[0], options.properties);
    return multiPolygon(result, options.properties);
}
/**
 * Calculates area overlap between a feature A and a feature array B.
 * Intersection is done in chunks on featuresB to avoid errors due to too many features
 * @param featureA single feature to intersect with featuresB
 * @param featuresB array of features
 * @param chunkSize Size of array to split featuresB into, avoids intersect failure due to large array)
 * @returns intersection of featureA with featuresB
 */
export const intersectInChunks = (featureA, featuresB, chunkSize) => {
    // chunk to avoid blowing up intersect
    const chunks = chunk(featuresB, chunkSize || 5000);
    // intersect chunks and flatten into single result
    return chunks.flatMap((curChunk) => {
        // MultiMerge will merge curChunk FC into a single multipolygon before intersection
        const rem = clipMultiMerge(featureA, featureCollection(curChunk), "intersection");
        return rem || [];
    });
};
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