Add initial ol.geom.simplify
This commit is contained in:
Tom Payne
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src/ol/geom/simplifygeom.js
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219
src/ol/geom/simplifygeom.js
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// Based on simplify-js https://github.com/mourner/simplify-js
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// Copyright (c) 2012, Vladimir Agafonkin
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice,
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// this list of conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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// POSSIBILITY OF SUCH DAMAGE.
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goog.provide('ol.geom.simplify');
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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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* @param {number} squaredTolerance Squared tolerance.
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* @param {boolean} highQuality Highest quality.
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* @param {Array.<number>=} opt_simplifiedFlatCoordinates Simplified flat
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* coordinates.
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* @return {Array.<number>} Simplified line string.
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*/
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ol.geom.simplify.lineString = function(flatCoordinates, offset, end, stride,
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squaredTolerance, highQuality, opt_simplifiedFlatCoordinates) {
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var simplifiedFlatCoordinates = goog.isDef(opt_simplifiedFlatCoordinates) ?
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opt_simplifiedFlatCoordinates : [];
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if (!highQuality) {
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end = ol.geom.simplify.radialDistance(flatCoordinates, offset, end,
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stride, squaredTolerance,
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simplifiedFlatCoordinates, 0);
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flatCoordinates = simplifiedFlatCoordinates;
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offset = 0;
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stride = 2;
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}
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simplifiedFlatCoordinates.length = ol.geom.simplify.douglasPeucker(
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flatCoordinates, offset, end, stride, squaredTolerance,
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simplifiedFlatCoordinates, 0);
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return simplifiedFlatCoordinates;
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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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* @param {number} squaredTolerance Squared tolerance.
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* @param {Array.<number>} simplifiedFlatCoordinates Simplified flat
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* coordinates.
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* @param {number} simplifiedOffset Simplified offset.
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* @return {number} Simplified offset.
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*/
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ol.geom.simplify.douglasPeucker = function(flatCoordinates, offset, end,
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stride, squaredTolerance, simplifiedFlatCoordinates, simplifiedOffset) {
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var n = (end - offset) / stride;
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if (n < 3) {
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for (; offset < end; offset += stride) {
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simplifiedFlatCoordinates[simplifiedOffset++] =
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flatCoordinates[offset];
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simplifiedFlatCoordinates[simplifiedOffset++] =
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flatCoordinates[offset + 1];
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}
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return simplifiedOffset;
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}
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var MarkerArray = goog.global['Uint8Array'] ? Uint8Array : Array;
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var markers = new MarkerArray(n);
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markers[0] = 1;
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markers[n - 1] = 1;
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var stack = [offset, end - stride];
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var index = 0;
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var i;
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while (stack.length > 0) {
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var last = stack.pop();
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var first = stack.pop();
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var maxSquaredDistance = 0;
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var x1 = flatCoordinates[first];
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var y1 = flatCoordinates[first + 1];
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var x2 = flatCoordinates[last];
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var y2 = flatCoordinates[last + 1];
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for (i = first + stride; i < last; i += stride) {
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var x = flatCoordinates[i];
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var y = flatCoordinates[i + 1];
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var squaredDistance =
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ol.geom.simplify.squaredSegmentDistance(x, y, x1, y1, x2, y2);
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if (squaredDistance > maxSquaredDistance) {
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index = i;
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maxSquaredDistance = squaredDistance;
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}
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}
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if (maxSquaredDistance > squaredTolerance) {
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markers[(index - offset) / stride] = 1;
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if (first + stride < index) {
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stack.push(first, index);
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}
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if (index + stride < last) {
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stack.push(index, last);
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}
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}
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}
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for (i = 0; i < n; ++i) {
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if (markers[i]) {
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simplifiedFlatCoordinates[simplifiedOffset++] =
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flatCoordinates[offset + i * stride];
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simplifiedFlatCoordinates[simplifiedOffset++] =
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flatCoordinates[offset + i * stride + 1];
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}
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}
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return simplifiedOffset;
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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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* @param {number} squaredTolerance Squared tolerance.
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* @param {Array.<number>} simplifiedFlatCoordinates Simplified flat
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* coordinates.
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* @param {number} simplifiedOffset Simplified offset.
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* @return {number} Simplified offset.
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*/
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ol.geom.simplify.radialDistance = function(flatCoordinates, offset, end,
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stride, squaredTolerance, simplifiedFlatCoordinates, simplifiedOffset) {
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if (end <= offset + stride) {
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// zero or one point, no simplification possible, so copy and return
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for (; offset < end; offset += stride) {
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simplifiedFlatCoordinates[simplifiedOffset++] = flatCoordinates[offset];
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simplifiedFlatCoordinates[simplifiedOffset++] =
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flatCoordinates[offset + 1];
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}
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return simplifiedOffset;
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}
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var x1 = flatCoordinates[offset];
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var y1 = flatCoordinates[offset + 1];
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// copy first point
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simplifiedFlatCoordinates[simplifiedOffset++] = x1;
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simplifiedFlatCoordinates[simplifiedOffset++] = y1;
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var x2 = x1;
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var y2 = y1;
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for (offset += stride; offset < end; offset += stride) {
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x2 = flatCoordinates[offset];
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y2 = flatCoordinates[offset + 1];
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if (ol.geom.simplify.squaredDistance(x1, y1, x2, y2) > squaredTolerance) {
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// copy point at offset
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simplifiedFlatCoordinates[simplifiedOffset++] = x2;
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simplifiedFlatCoordinates[simplifiedOffset++] = y2;
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x1 = x2;
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y1 = y2;
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}
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}
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if (x2 != x1 || y2 != y1) {
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// copy last point
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simplifiedFlatCoordinates[simplifiedOffset++] = x2;
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simplifiedFlatCoordinates[simplifiedOffset++] = y2;
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}
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return simplifiedOffset;
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};
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/**
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* Returns the square of the distance between the points (x1, y1) and (x2, y2).
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* @param {number} x1 X1.
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* @param {number} y1 Y1.
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* @param {number} x2 X2.
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* @param {number} y2 Y2.
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* @return {number} Squared distance.
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*/
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ol.geom.simplify.squaredDistance = function(x1, y1, x2, y2) {
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var dx = x2 - x1;
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var dy = y2 - y1;
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return dx * dx + dy * dy;
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};
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/**
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* Returns the square of the closest distance between the point (x, y) and the
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* line segment (x1, y1) to (x2, y2).
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* @param {number} x X.
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* @param {number} y Y.
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* @param {number} x1 X1.
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* @param {number} y1 Y1.
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* @param {number} x2 X2.
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* @param {number} y2 Y2.
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* @return {number} Squared distance.
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*/
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ol.geom.simplify.squaredSegmentDistance = function(x, y, x1, y1, x2, y2) {
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var dx = x2 - x1;
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var dy = y2 - y1;
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if (dx !== 0 || dy !== 0) {
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var t = ((x - x1) * dx + (y - y1) * dy) / (dx * dx + dy * dy);
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if (t > 1) {
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x1 = x2;
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y1 = y2;
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} else if (t > 0) {
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x1 += dx * t;
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y1 += dy * t;
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}
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}
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return ol.geom.simplify.squaredDistance(x, y, x1, y1);
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};
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