/**
* Return the inward-facing normal of the great circle passing through the
* edge from vertex k to vertex k+1 (mod 4). The normals returned by
* GetEdgeRaw are not necessarily unit length.
*
* If this is not a leaf cell, set children[0..3] to the four children of
* this cell (in traversal order) and return true. Otherwise returns false.
* This method is equivalent to the following:
*
* for (pos=0, id=child_begin(); id != child_end(); id = id.next(), ++pos)
* children[i] = S2Cell(id);
*
* except that it is more than two times faster.
* @param S2Cell[] $children
*/
public function subdivide(&$children)
{
// This function is equivalent to just iterating over the child cell ids
// and calling the S2Cell constructor, but it is about 2.5 times faster.
if ($this->cellId->isLeaf()) {
return false;
}
// Compute the cell midpoint in uv-space.
$uvMid = $this->getCenterUV();
// Create four children with the appropriate bounds.
/** @var S2CellId $id */
$id = $this->cellId->childBegin();
for ($pos = 0; $pos < 4; ++$pos, $id = $id->next()) {
$child =& $children[$pos];
$child->face = $this->face;
$child->level = $this->level + 1;
$new_o = S2::posToOrientation($pos);
$child->orientation = $this->orientation ^ $new_o;
// echo "this-ori:" . $this->orientation . " new_o:" . $new_o . " res:" . $child->orientation . "\n";
$child->cellId = $id;
$ij = S2::posToIJ($this->orientation, $pos);
for ($d = 0; $d < 2; ++$d) {
// The dimension 0 index (i/u) is in bit 1 of ij.
$m = 1 - ($ij >> 1 - $d & 1);
$child->uv[$d][$m] = $uvMid->get($d);
$child->uv[$d][1 - $m] = $this->uv[$d][1 - $m];
}
}
return true;
}
