Calculate volume in maya

// iphone_bumper faces = 14786 //
// TOTAL VOLUME = 4.404315761 //
// 4.404316 // 

// iphone_case faces = 14838 //
// TOTAL VOLUME = 13.99083778 //
// Result: 13.990838 // 

global proc vector faceNormal(string $face ) {
    string $res[] = `polyInfo -fn $face`;
    string $buff[];
    tokenize($res[0] ,":" , $buff);
    tokenize($buff[1] ," " , $buff);
    return unit( << float($buff[0]) , float($buff[1]) ,float($buff[2]) >>);
}

global proc float xyArea(vector $v1,vector $v2,vector $v3 ) {
    return abs((($v1.x)*(($v3.y)-($v2.y)))+(($v2.x)*(($v1.y)-($v3.y)))+(($v3.x)*(($v2.y)-($v1.y)))) *0.5;
}


global proc float prismVolume(string $triangle) {
    string $triVerts[] = `polyListComponentConversion -tv $triangle`;
    $triVerts = `ls -flatten $triVerts`;

    if (`size $triVerts` != 3) error($triangle +" is not a triangle");

    vector $v1 = `pointPosition -w $triVerts[0]`; 
    vector $v2 = `pointPosition -w $triVerts[1]`; 
    vector $v3 = `pointPosition -w $triVerts[2]`; 

    vector $normal = faceNormal( $triangle );
    float $area = xyArea( $v1, $v2, $v3 );
    float $pVolume = ((($v1.z)+($v2.z)+($v3.z))/3.0)*$area ;
    if (($normal.z) < 0) $pVolume = -$pVolume;

    return $pVolume;
}

// pick a mesh and type meshVolume();
global proc float meshVolume() {
     string $sel[] = `ls -sl -dag -leaf -type "mesh"`;
     string $dup[] = `duplicate -rr $sel[0]`;
     makeIdentity -apply true -t 1 -r 1 -s 1 -n 0 $dup[0]; //freeze
     polyTriangulate $dup[0];
     string $tris[] = `ls -flatten ($dup[0] +".f[*]")`;

     float $volume = 0.0;
     for ($t in $tris) $volume += prismVolume($t) ;

     delete $dup;
     return $volume;
}

// Result: 4.404317 // 

// Result: 13.990835 //