pocketmine\entity\Entity::checkGroundState PHP Method

    protected function checkGroundState($movX, $movY, $movZ, $dx, $dy, $dz)
    {
        $this->isCollidedVertically = $movY != $dy;
        $this->isCollidedHorizontally = ($movX != $dx or $movZ != $dz);
        $this->isCollided = ($this->isCollidedHorizontally or $this->isCollidedVertically);
        $this->onGround = ($movY != $dy and $movY < 0);
    }