219 lines
6.2 KiB
PHP
219 lines
6.2 KiB
PHP
<?php
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/**
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* PHP Shapefile - PHP library to read and write ESRI Shapefiles, compatible with WKT and GeoJSON
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*
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* @package Shapefile
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* @author Gaspare Sganga
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* @version 4.0.0dev
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* @license MIT
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* @link https://gasparesganga.com/labs/php-shapefile/
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*/
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namespace Shapefile\Geometry;
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use Shapefile\Shapefile;
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use Shapefile\ShapefileException;
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/**
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* Linestring Geometry.
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*
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* - Array: [
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* [numpoints] => int
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* [points] => [
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* [
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* [x] => float
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* [y] => float
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* [z] => float
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* [m] => float/bool
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* ]
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* ]
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* ]
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*
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* - WKT:
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* LINESTRING [Z][M] (x y z m, x y z m)
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*
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* - GeoJSON:
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* {
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* "type": "LineString" / "LineStringM"
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* "coordinates": [
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* [x, y, z] / [x, y, m] / [x, y, z, m]
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* ]
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* }
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*/
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class Linestring extends MultiPoint
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{
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/**
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* WKT and GeoJSON basetypes, collection class type
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*/
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const WKT_BASETYPE = 'LINESTRING';
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const GEOJSON_BASETYPE = 'LineString';
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const COLLECTION_CLASS = 'Point';
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/////////////////////////////// PUBLIC ///////////////////////////////
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/**
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* Checks whether the linestring is a closed ring or not.
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* A closed ring has at least 4 vertices and the first and last ones must be the same.
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*
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* @return bool
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*/
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public function isClosedRing()
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{
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return $this->getNumPoints() >= 4 && $this->getPoint(0) == $this->getPoint($this->getNumPoints() - 1);
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}
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/**
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* Forces the linestring to be a closed ring.
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*
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* @return self Returns $this to provide a fluent interface.
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*/
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public function forceClosedRing()
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{
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if (!$this->checkRingNumPoints()) {
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throw new ShapefileException(Shapefile::ERR_GEOM_RING_NOT_ENOUGH_VERTICES);
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}
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if (!$this->isClosedRing()) {
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$this->addPoint($this->getPoint(0));
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}
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return $this;
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}
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/**
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* Checks whether a ring is clockwise or not (it works with open rings too).
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*
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* Throws an exception if ring area is too small and cannot determine its orientation.
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* Returns Shapefile::UNDEFINED or throw an exception if there are not enough points.
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*
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* @param bool $flag_throw_exception Optional flag to throw an exception if there are not enough points.
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*
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* @return bool|Shapefile::UNDEFINED
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*/
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public function isClockwise($flag_throw_exception = false)
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{
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if ($this->isEmpty()) {
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return Shapefile::UNDEFINED;
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}
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if (!$this->checkRingNumPoints()) {
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if ($flag_throw_exception) {
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throw new ShapefileException(Shapefile::ERR_GEOM_RING_NOT_ENOUGH_VERTICES);
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}
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return Shapefile::UNDEFINED;
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}
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$area = $this->computeGaussArea($this->getArray()['points']);
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if (!$area) {
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throw new ShapefileException(Shapefile::ERR_GEOM_RING_AREA_TOO_SMALL);
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}
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// Negative area means clockwise direction
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return $area < 0;
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}
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/**
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* Forces the ring to be in clockwise direction (it works with open rings too).
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* Throws an exception if direction is undefined.
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*
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* @return self Returns $this to provide a fluent interface.
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*/
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public function forceClockwise()
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{
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if ($this->isClockwise(true) === false) {
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$this->reverseGeometries();
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}
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return $this;
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}
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/**
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* Forces the ring to be in counterclockwise direction (it works with open rings too).
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* Throws an exception if direction is undefined.
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*
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* @return self Returns $this to provide a fluent interface.
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*/
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public function forceCounterClockwise()
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{
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if ($this->isClockwise(true) === true) {
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$this->reverseGeometries();
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}
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return $this;
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}
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public function getSHPBasetype()
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{
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return Shapefile::SHAPE_TYPE_POLYLINE;
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}
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/////////////////////////////// PROTECTED ///////////////////////////////
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protected function getWKTBasetype()
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{
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return static::WKT_BASETYPE;
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}
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protected function getGeoJSONBasetype()
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{
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return static::GEOJSON_BASETYPE;
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}
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protected function getCollectionClass()
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{
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return __NAMESPACE__ . '\\' . static::COLLECTION_CLASS;
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}
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/////////////////////////////// PRIVATE ///////////////////////////////
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/**
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* Checks if the linestring has enough points to be a ring.
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*/
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private function checkRingNumPoints()
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{
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return $this->getNumPoints() >= 3;
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}
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/**
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* Computes ring area using a Gauss-like formula.
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* The target is to determine whether it is positive or negative, not the exact area.
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*
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* An optional $exp parameter is used to deal with very small areas.
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*
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* @param array $points Array of points. Each element must have "x" and "y" members.
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* @param int $exp Optional exponent to deal with small areas (coefficient = 10^exponent).
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*
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* @return float
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*/
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private function computeGaussArea($points, $exp = 0)
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{
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// If a coefficient of 10^12 is not enough, give up!
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if ($exp > 12) {
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return 0;
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}
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$coef = pow(10, $exp);
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// At least 3 points (in case of an open ring) are needed to compute the area
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$num_points = count($points);
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if ($num_points < 3) {
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return 0;
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}
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// Use Gauss's area formula (no need to be strict here, hence no 1/2 coefficient and no check for closed rings)
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$num_points--;
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$tot = 0;
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for ($i = 0; $i < $num_points; ++$i) {
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$tot += ($coef * $points[$i]['x'] * $points[$i + 1]['y']) - ($coef * $points[$i]['y'] * $points[$i + 1]['x']);
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}
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$tot += ($coef * $points[$num_points]['x'] * $points[0]['y']) - ($coef * $points[$num_points]['y'] * $points[0]['x']);
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// If area is too small, increase coefficient exponent and retry
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if ($tot == 0) {
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return $this->computeGaussArea($points, $exp + 3);
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}
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return $tot;
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}
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}
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