Largest-Triangle-Three Bucket Downsampling Graphs in C#

public static IEnumerable<Tuple<double, double>> LargestTriangleThreeBuckets(List<Tuple<double, double>> data, int threshold)
{ int dataLength = data.Count; if (threshold >= dataLength || threshold == 0) return data; // Nothing to do

List<Tuple<double, double>> sampled = new List<Tuple<double, double>>(threshold);

// Bucket size. Leave room for start and end data points
double every = (double)(dataLength - 2) / (threshold - 2);

int a = 0;
Tuple<double, double> maxAreaPoint = new Tuple<double, double>(0,0);
int nextA = 0;

sampled.Add(data[a]); // Always add the first point

for (int i = 0; i < threshold - 2; i++)
{
    // Calculate point average for next bucket (containing c)
    double avgX = 0;
    double avgY = 0;
    int avgRangeStart = (int)(Math.Floor((i + 1) * every) + 1);
    int avgRangeEnd = (int)(Math.Floor((i + 2) * every) + 1);
    avgRangeEnd = avgRangeEnd < dataLength ? avgRangeEnd : dataLength;

    int avgRangeLength = avgRangeEnd - avgRangeStart;

    for (; avgRangeStart < avgRangeEnd; avgRangeStart++)
    {
        avgX += data[avgRangeStart].Item1; // * 1 enforces Number (value may be Date)
        avgY += data[avgRangeStart].Item2;
    }
    avgX /= avgRangeLength;

    avgY /= avgRangeLength;

    // Get the range for this bucket
    int rangeOffs = (int)(Math.Floor((i + 0) * every) + 1);
    int rangeTo = (int)(Math.Floor((i + 1) * every) + 1);

    // Point a
    double pointAx = data[a].Item1; // enforce Number (value may be Date)
    double pointAy = data[a].Item2;

    double maxArea = -1;

    for (; rangeOffs < rangeTo; rangeOffs++)
    {
        // Calculate triangle area over three buckets
        double area = Math.Abs((pointAx - avgX) * (data[rangeOffs].Item2 - pointAy) -
                               (pointAx - data[rangeOffs].Item1) * (avgY - pointAy)
                          ) * 0.5;
        if (area > maxArea)
        {
            maxArea = area;
            maxAreaPoint = data[rangeOffs];
            nextA = rangeOffs; // Next a is this b
        }
    }

    sampled.Add(maxAreaPoint); // Pick this point from the bucket
    a = nextA; // This a is the next a (chosen b)
}

sampled.Add(data[dataLength - 1]); // Always add last

return sampled;

}