/**
* Douglas-Peuker polyline simplification algorithm. First draws single line
* from start to end. Then finds largest deviation from this straight line, and if
* greater than tolerance, includes that point, splitting the original line into
* two new lines. Repeats recursively for each new line created.
*
* @param int $start_vertex_index
* @param int $end_vertex_index
*/
private function DouglasPeucker($start_vertex_index, $end_vertex_index)
{
if ($end_vertex_index <= $start_vertex_index + 1) {
// there is nothing to simplify
return;
}
// Make line from start to end
$line = new Line($this->original_points[$start_vertex_index], $this->original_points[$end_vertex_index]);
// Find largest distance from intermediate points to this line
$max_dist_to_line_squared = 0;
for ($index = $start_vertex_index + 1; $index < $end_vertex_index - 1; $index++) {
$dist_to_line_squared = $line->DistanceToPointSquared($this->original_points[$index]);
if ($dist_to_line_squared > $max_dist_to_line_squared) {
$max_dist_to_line_squared = $dist_to_line_squared;
$max_dist_index = $index;
}
}
// Check max distance with tolerance
if ($max_dist_to_line_squared > $this->tolerance_squared) {
// split the polyline at the farthest vertex from S
$this->original_points[$max_dist_index]->include = true;
// recursively simplify the two subpolylines
$this->DouglasPeucker($start_vertex_index, $max_dist_index);
$this->DouglasPeucker($max_dist_index, $end_vertex_index);
}
// else the approximation is OK, so ignore intermediate vertices
}
