/**
* Populate the children of "candidate" by expanding the given number of
* levels from the given cell. Returns the number of children that were marked
* "terminal".
*/
private function expandChildren(Candidate $candidate, S2Cell $cell, $numLevels)
{
$numLevels--;
$childCells = array();
for ($i = 0; $i < 4; ++$i) {
$childCells[$i] = new S2Cell();
}
$cell->subdivide($childCells);
$numTerminals = 0;
for ($i = 0; $i < 4; ++$i) {
if ($numLevels > 0) {
if ($this->region->mayIntersect($childCells[$i])) {
$numTerminals += $this->expandChildren($candidate, $childCells[$i], $numLevels);
}
continue;
}
$child = $this->newCandidate($childCells[$i]);
// echo "child for " . $childCells[$i] . " is " . $child . "\n";
if ($child != null) {
$candidate->children[$candidate->numChildren++] = $child;
if ($child->isTerminal) {
++$numTerminals;
}
}
}
return $numTerminals;
}
