[Javascript] Calculate area coverage polygon object

Hi all,

In case your splines do not auto-intersect, try this:

var pathArea = function(/*[x,y][3][]*/ep,  r,n,i,P,Q,xa,ya,xb,yb,xc,yc,xd,yd)
//----------------------------------
// Based on http://www.gust.org.pl/bachotex/2011-en/presentations/JackowskiB_3c_2011
// Return AREA x 20 ; result is signed.
{
    for( r=0, n=ep.length, i=-1 ; ++i < n ; )
    {
        3 == (P=ep).length ?
            ( xa=P[1][0], ya=P[1][1], xb=P[2][0], yb=P[2][1] ) :
            ( xa=xb=P[0], ya=yb=P[1]);
        3 == (Q=ep[(1+i)%n]).length ?
            ( xc=Q[0][0], yc=Q[0][1], xd=Q[1][0], yd=Q[1][1] ) :
            ( xc=xd=Q[0], yc=yd=Q[1]);
        
        r += (xb-xa)*(10*ya + 6*yb + 3*yc +    yd)
          +  (xc-xb)*( 4*ya + 6*yb + 6*yc +  4*yd)
          +  (xd-xc)*(   ya + 3*yb + 6*yc + 10*yd);
    }
    return r;
};
var splineArea = function(/*SplineItem*/o,  a,r,i,n,t)
//----------------------------------
// Visit every closed path and calculate the total area.
{
    const CLOSED = +PathType.CLOSED_PATH;
    a = o.paths.everyItem().getElements();
    for( r=0, n=a.length, i=-1 ; ++i < n && (t=a).pathType==CLOSED ; r+=pathArea(t.entirePath) );
    if( i < n ) throw "All paths must be closed.";
    return (r/=20), 0 < r ? r : -r;
};
var getArea = function(/*obj|obj[]*/a,t,mu,i,r)
//----------------------------------
// Main function. Return the area in the form "<value> <unit>²".
// This function does not address splines that auto-intersect.
{
    callee.Q||(callee.Q={
        Q:               'q',
        U:               'u',
        POINTS:          'pt',
        PIXELS:          'px',
        PICAS:           'p',
        MILS:            'mils',
        MILLIMETERS:     'mm',
        INCHES_DECIMEL:  'in',
        INCHES:          'in',
        HA:              'ha',
        CICEROS:         'c',
        CENTIMETERS:     'cm',
        BAI:             'bai',
        AMERICAN_POINTS: 'ap',
        AGATES:          'ag',
        });
    (a instanceof Array) || (a=);
    // Set consistent measurement unit.
    // ---
    while( 1 )
    {
        if( !(t=a[0]) || 'function' != typeof t.toSpecifier ) throw "Invalid input."
        t = t.toSpecifier().match(/^\/document\[@id=\d+\]/);
        if( !t || !(t=resolve(t[0])) || !(t instanceof Document) ) throw "Invalid input.";
        t = t.viewPreferences.horizontalMeasurementUnits;
        app.scriptPreferences.measurementUnit = t;
        mu = callee.Q[t.toString()]||'';
        mu && (mu = ' ' + mu + '\xB2');
        break;
    }
    
    for( r=0, i=a.length ; i-- ; (o=a)&&o.hasOwnProperty('paths')&&(r+=splineArea(o)) );
    
    return String(r) + mu;
};
// TEST. (Assuming something is selected.)
//========================================
var sel = app.selection;
alert( getArea(sel) );

Hope that helps.

Best,

Marc