61 lines
1.6 KiB
JavaScript
61 lines
1.6 KiB
JavaScript
/**
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* @module ol/geom/flat/area
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*/
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/**
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* @param {Array<number>} flatCoordinates Flat coordinates.
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* @param {number} offset Offset.
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* @param {number} end End.
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* @param {number} stride Stride.
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* @return {number} Area.
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*/
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export function linearRing(flatCoordinates, offset, end, stride) {
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let twiceArea = 0;
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const x0 = flatCoordinates[end - stride];
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const y0 = flatCoordinates[end - stride + 1];
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let dx1 = 0;
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let dy1 = 0;
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for (; offset < end; offset += stride) {
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const dx2 = flatCoordinates[offset] - x0;
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const dy2 = flatCoordinates[offset + 1] - y0;
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twiceArea += dy1 * dx2 - dx1 * dy2;
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dx1 = dx2;
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dy1 = dy2;
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}
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return twiceArea / 2;
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}
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/**
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* @param {Array<number>} flatCoordinates Flat coordinates.
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* @param {number} offset Offset.
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* @param {Array<number>} ends Ends.
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* @param {number} stride Stride.
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* @return {number} Area.
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*/
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export function linearRings(flatCoordinates, offset, ends, stride) {
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let area = 0;
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for (let i = 0, ii = ends.length; i < ii; ++i) {
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const end = ends[i];
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area += linearRing(flatCoordinates, offset, end, stride);
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offset = end;
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}
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return area;
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}
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/**
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* @param {Array<number>} flatCoordinates Flat coordinates.
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* @param {number} offset Offset.
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* @param {Array<Array<number>>} endss Endss.
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* @param {number} stride Stride.
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* @return {number} Area.
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*/
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export function linearRingss(flatCoordinates, offset, endss, stride) {
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let area = 0;
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for (let i = 0, ii = endss.length; i < ii; ++i) {
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const ends = endss[i];
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area += linearRings(flatCoordinates, offset, ends, stride);
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offset = ends[ends.length - 1];
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}
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return area;
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}
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