ol/geom/flat/orient.js

OpenLayers mapping library

/**
 * @module ol/geom/flat/orient
 */
import { coordinates as reverseCoordinates } from './reverse.js';
/**
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {number} end End.
 * @param {number} stride Stride.
 * @return {boolean} Is clockwise.
 */
export function linearRingIsClockwise(flatCoordinates, offset, end, stride) {
    // http://tinyurl.com/clockwise-method
    // https://github.com/OSGeo/gdal/blob/trunk/gdal/ogr/ogrlinearring.cpp
    var edge = 0;
    var x1 = flatCoordinates[end - stride];
    var y1 = flatCoordinates[end - stride + 1];
    for (; offset < end; offset += stride) {
        var x2 = flatCoordinates[offset];
        var y2 = flatCoordinates[offset + 1];
        edge += (x2 - x1) * (y2 + y1);
        x1 = x2;
        y1 = y2;
    }
    return edge > 0;
}
/**
 * Determines if linear rings are oriented.  By default, left-hand orientation
 * is tested (first ring must be clockwise, remaining rings counter-clockwise).
 * To test for right-hand orientation, use the `opt_right` argument.
 *
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<number>} ends Array of end indexes.
 * @param {number} stride Stride.
 * @param {boolean=} opt_right Test for right-hand orientation
 *     (counter-clockwise exterior ring and clockwise interior rings).
 * @return {boolean} Rings are correctly oriented.
 */
export function linearRingsAreOriented(flatCoordinates, offset, ends, stride, opt_right) {
    var right = opt_right !== undefined ? opt_right : false;
    for (var i = 0, ii = ends.length; i < ii; ++i) {
        var end = ends[i];
        var isClockwise = linearRingIsClockwise(flatCoordinates, offset, end, stride);
        if (i === 0) {
            if ((right && isClockwise) || (!right && !isClockwise)) {
                return false;
            }
        }
        else {
            if ((right && !isClockwise) || (!right && isClockwise)) {
                return false;
            }
        }
        offset = end;
    }
    return true;
}
/**
 * Determines if linear rings are oriented.  By default, left-hand orientation
 * is tested (first ring must be clockwise, remaining rings counter-clockwise).
 * To test for right-hand orientation, use the `opt_right` argument.
 *
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<Array<number>>} endss Array of array of end indexes.
 * @param {number} stride Stride.
 * @param {boolean=} opt_right Test for right-hand orientation
 *     (counter-clockwise exterior ring and clockwise interior rings).
 * @return {boolean} Rings are correctly oriented.
 */
export function linearRingssAreOriented(flatCoordinates, offset, endss, stride, opt_right) {
    for (var i = 0, ii = endss.length; i < ii; ++i) {
        var ends = endss[i];
        if (!linearRingsAreOriented(flatCoordinates, offset, ends, stride, opt_right)) {
            return false;
        }
        if (ends.length) {
            offset = ends[ends.length - 1];
        }
    }
    return true;
}
/**
 * Orient coordinates in a flat array of linear rings.  By default, rings
 * are oriented following the left-hand rule (clockwise for exterior and
 * counter-clockwise for interior rings).  To orient according to the
 * right-hand rule, use the `opt_right` argument.
 *
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<number>} ends Ends.
 * @param {number} stride Stride.
 * @param {boolean=} opt_right Follow the right-hand rule for orientation.
 * @return {number} End.
 */
export function orientLinearRings(flatCoordinates, offset, ends, stride, opt_right) {
    var right = opt_right !== undefined ? opt_right : false;
    for (var i = 0, ii = ends.length; i < ii; ++i) {
        var end = ends[i];
        var isClockwise = linearRingIsClockwise(flatCoordinates, offset, end, stride);
        var reverse = i === 0 ?
            (right && isClockwise) || (!right && !isClockwise) :
            (right && !isClockwise) || (!right && isClockwise);
        if (reverse) {
            reverseCoordinates(flatCoordinates, offset, end, stride);
        }
        offset = end;
    }
    return offset;
}
/**
 * Orient coordinates in a flat array of linear rings.  By default, rings
 * are oriented following the left-hand rule (clockwise for exterior and
 * counter-clockwise for interior rings).  To orient according to the
 * right-hand rule, use the `opt_right` argument.
 *
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<Array<number>>} endss Array of array of end indexes.
 * @param {number} stride Stride.
 * @param {boolean=} opt_right Follow the right-hand rule for orientation.
 * @return {number} End.
 */
export function orientLinearRingsArray(flatCoordinates, offset, endss, stride, opt_right) {
    for (var i = 0, ii = endss.length; i < ii; ++i) {
        offset = orientLinearRings(flatCoordinates, offset, endss[i], stride, opt_right);
    }
    return offset;
}
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