Function getArea

alg/gdalwarpkernel.cpp:1019–1035

poly may or may not be closed.

// poly may or may not be closed.
static double getArea(const XYPoly &poly)
{
    // CPLAssert(poly.size() >= 2);
    const size_t nPointCount = poly.size();
    double dfAreaSum =
        poly[0].first * (poly[1].second - poly[nPointCount - 1].second);

    for (size_t i = 1; i < nPointCount - 1; i++)
    {
        dfAreaSum += poly[i].first * (poly[i + 1].second - poly[i - 1].second);
    }

    dfAreaSum += poly[nPointCount - 1].first *
                 (poly[0].second - poly[nPointCount - 2].second);

    return 0.5 * std::fabs(dfAreaSum);
}

/************************************************************************/
/*                       CanUse4SamplesFormula()                        */