Area Of A Polygon / Triangle

[fred22]

I know this is really a maths question, does anyone have a good way to measure the area of a polygon.

So either a polygon mesh surface
A curve.

I'm trying to weed out some linear curves that have a maxium area, I've tried this in mel but had little success.

Cheers

[daniel-faust]

The method double MFnNurbsCurve:: area ( double tolerance, MStatus * ReturnStatus ) const
calculates the area of a curve, there's also one for a NurbsSurface.

[fred22]

thanks heaps.

[rob-bateman]

either MItMeshPolygon::getArea() to get the area, or split the poly into triangles, calculate each tirangles face normal using the cross product (but do not normalise!). The area of the triangle is the length of the normal (or possibly half the length, can't remember). Sum the area of each triagle to get the area of the polygon.

[joojaa]

Theres actualy a script in maya unsupported folder that does calculate the area for polymeshes, aswell as one thet calculates volume.

You also have acces to the area functor in mel.

And yes its 1/2 of the length (length would eb the area of the paralellogram that results form the vector a, vector a+b,vector b and finaly their common origin)

However even if there is a function to calculate teh area of a curve, im a bit confused a closed spacecurve HAS no sane area defied. So what is it they realy calculate. (infact by math definitien a curve hasnt gota area it can bound one tough, but a space curve cant bound a area very well since i can understad what the area is if its flat but i cant for the earth of me figure out what the area of a bent spacecurve is its like asking for the volume of a circle)

[fred22]

So this is what I ended up with but unfortinatly I could not get it to return any area what so ever on as many variations of curve I tried.......

If anybody is familar with autocad there is such a tool that allows getting the area of a curve.....

CODE
//
// Copyright (C) Matt Blair
//
// File: curveAreaCmdCmd.cpp
//
// MEL Command: curveAreaCmd
//
// Author: Maya Plug-in Wizard 2.0
//

// Includes everything needed to register a simple MEL command with Maya.
//
#include
#include
#include
#include
#include
#include
#include

// Use helper macro to register a command with Maya.  It creates and
// registers a command that does not support undo or redo.  The
// created class derives off of MPxCommand.
//
DeclareSimpleCommand( curveArea, "Matt Blair", "7.0");

MStatus curveArea::doIt( const MArgList& args )
//
//    Description:
//        implements the MEL curveAreaCmd command.
//
//    Arguments:
//        args - the argument list that was passes to the command from MEL
//
//    Return Value:
//        MS::kSuccess - command succeeded
//        MS::kFailure - command failed (returning this value will cause the
//                     MEL script that is being run to terminate unless the
//                     error is caught using a "catch" statement.
//
{
    MStatus stat = MS::kSuccess;

    MSelectionList selection;
    MGlobal::getActiveSelectionList( selection );

    MDagPath dagPath;
    MObject component;

    double area, length;
    MString txt;
    MItSelectionList iter( selection );

    for (; !iter.isDone(); iter.next() )
    {
        iter.getDagPath( dagPath, component );

        MFnNurbsCurve curveFn( dagPath, &stat );
        if ( stat )
        {
            area = curveFn.area( 0.1, &stat );
            length = curveFn.length( 0.001, &stat );
        }
    }

    txt += "Area: ";
    txt += area;
    txt += "\nLength: ";
    txt += length;
    txt += "\n";

    clearResult;
    MGlobal::displayInfo( txt );
    setResult( area );

    return stat;
}

[fred22]

I'm now using MItMeshPolygon::getArea()

Its a really simple plugin. But I'm having trouble with arguments for the method.
The documentation states....
MStatus MItMeshPolygon::getArea ( double &area, MSpace::Space space )

If I am to get the area via

CODE
double area;
area += poyIter.getArea( ??, MSpace::kWorld);

Or am I supposed to.....

CODE
double area;
poyIter.getArea( area, MSpace::kWorld);

Both of which return the result but not the total of multiple selections. The goal is to get the total area of the selected faces.