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Manually implemented PointOnSurface() function as it is not yet implemented in MySQL

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This commit is contained in:
Madhura Jayaratne 2011-07-09 19:18:03 +05:30
parent faced3027a
commit c81db372d7
2 changed files with 63 additions and 38 deletions
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44
libraries/gis/pma_gis_multipolygon.php
View File

@ -376,7 +376,12 @@ class PMA_GIS_Multipolygon extends PMA_GIS_Geometry
$row_data['parts'][$i]['isOuter'] = PMA_GIS_Polygon::isOuterRing($ring['points']);
}
$this->getPointsOnSurface($row_data['parts']);
// Find points on surface for inner rings
foreach ($row_data['parts'] as $i => $ring) {
if (! $ring['isOuter']) {
$row_data['parts'][$i]['pointOnSurface'] = PMA_GIS_Polygon::getPointOnSurface($ring['points']);
}
}
// Classify inner rings to their respective outer rings.
foreach ($row_data['parts'] as $j => $ring1) {
@ -429,43 +434,6 @@ class PMA_GIS_Multipolygon extends PMA_GIS_Geometry
return $wkt;
}
/**
* Attach to each ring a point on its surface.
*
* @param array $rings
*/
private function getPointsOnSurface(&$rings)
{
$sql = 'SELECT ';
$inner_rings = false;
foreach ($rings as $i => $ring) {
if (! $ring['isOuter']) {
$inner_rings = true;
// gis_data[0]['MULTIPOLYGON'][0][0] will have $ring
$gis_data = array(array('MULTIPOLYGON' => array(array($ring['points']))));
$gis_data[0]['MULTIPOLYGON'][0][0]['no_of_points'] = count($ring['points']);
$geom = $this->generateWkt($gis_data, 0);
$sql .= 'AsText(PointOnSurface(GeomFromText("' . $geom . '"))) as `P' . $i . '`, ';
}
}
if (! $inner_rings) {
return;
}
$sql = substr($sql, 0, strlen($sql) - 2);
$result = PMA_DBI_fetch_result($sql);
require_once './libraries/gis/pma_gis_point.php';
$point = PMA_GIS_Point::singleton();
foreach ($rings as $i => $ring) {
if (! $ring['isOuter']) {
$param = $point->generateParams($result[0]['P' . $i], 0);
$rings[$i]['pointOnSurface'] = $param[0]['POINT'];
}
}
}
/**
* Generate parameters for the GIS data editor from the value of the GIS column.
*

57
libraries/gis/pma_gis_polygon.php
View File

@ -418,6 +418,63 @@ class PMA_GIS_Polygon extends PMA_GIS_Geometry
}
}
/**
* Returns a point that is guaranteed to be on the surface of the ring.
* (for simple closed rings)
*
* @param array $ring array of points forming the ring
*/
public static function getPointOnSurface($ring)
{
// Find two consecutive distinct points.
for ($i = 0; $i < count($ring) - 1; $i++) {
if (($ring[$i]['x'] != $ring[$i + 1]['x'])
|| ($ring[$i]['y'] != $ring[$i + 1]['y'])
) {
$x0 = $ring[$i]['x'];
$x1 = $ring[$i + 1]['x'];
$y0 = $ring[$i]['y'];
$y1 = $ring[$i + 1]['y'];
}
}
if (! isset($x0)) {
return false;
}
// Find the mid point
$x2 = ($x0 + $x1) / 2;
$y2 = ($y0 + $y1) / 2;
// Always keep $epsilon < 1 to go with the reduction logic found later in this method
$epsilon = 0.1;
$denominator = sqrt(pow(($y1 - $y0), 2) + pow(($x0 - $x1), 2));
$pointA = array(); $pointB = array();
while (true) {
// Get the points on either sides of the line with a distance of epsilon to the mid point
$pointA['x'] = $x2 + ($epsilon * ($y1 - $y0)) / $denominator;
$pointA['y'] = $y2 + ($pointA['x'] - $x2) * ($x0 - $x1) / ($y1 - $y0);
$pointB['x'] = $x2 + ($epsilon * ($y1 - $y0)) / (0 - $denominator);
$pointB['y'] = $y2 + ($pointB['x'] - $x2) * ($x0 - $x1) / ($y1 - $y0);
// One of the points should be inside the polygon, unless epcilon chosen is too large
if (PMA_GIS_Polygon::isPointInsidePolygon($pointA, $ring)) {
return $pointA;
} else if (PMA_GIS_Polygon::isPointInsidePolygon($pointB, $ring)) {
return $pointB;
}
// If both are outside the polygon reduce the epsilon and recalculate the points
// (reduce exponentially for faster convergance)
else {
$epsilon = pow($epsilon, 2);
}
}
}
/** Generate parameters for the GIS data editor from the value of the GIS column.
*
* @param string $value of the GIS column