src/Maths/Geometry/Quadrilateral.php
public function getFirstDiagonal()
    {
        $a = 'a';
        $c = 'c';
        $directions = Maths::getDirectionByPoints($this->getPointA(), $this->getPointC());
        if ($directions[0]==-1) {
            $a = 'c';
            $c = 'a';
        }
        try {
            return $this->getSegment($a, $c);
        } catch (\InvalidArgumentException $e) {
            throw $e;
        }
    }
public function getFirstDiagonal()
    {
        $a = 'a';
        $c = 'c';
        $directions = Maths::getDirectionByPoints($this->getPointA(), $this->getPointC());
        if ($directions[0]==-1) {
            $a = 'c';
            $c = 'a';
        }
        try {
            return $this->getSegment($a, $c);
        } catch (\InvalidArgumentException $e) {
            throw $e;
        }
    }
Get the [A->C] diagonal as a Segment with a positive direction(s)

@return  Segment
@throws  \InvalidArgumentException caught on Segment creation