你帮我在C#里面设计一个角度减法的函数，原始数据是double型的，格式如下：180.0000（整数位是度，前两位小数是分，最后两位是秒）

在C#中，你可以创建一个名为`SubtractAngles`的函数，专门用于处理这种格式的角度减法。首先，我们需要将输入的字符串按照度、分、秒分开，并转换成对应的double值。然后，进行角度相减，注意保持结果在0到360度之间（考虑到角度可以循环）。以下是函数的基本设计：

using System;
using System.Globalization;

public class AngleHelper
{
    public static string SubtractAngles(string angle1, string angle2)
    {
        // 将输入字符串分割并转换成double
        double degrees1, minutes1, seconds1, degrees2, minutes2, seconds2;
        if (!ParseAngle(angle1, out degrees1, out minutes1, out seconds1) ||
            !ParseAngle(angle2, out degrees2, out minutes2, out seconds2))
        {
            throw new ArgumentException("Invalid angle format.");
        }

        // 计算角度差
        double differenceDegrees = degrees1 - degrees2;
        double differenceSeconds = (degrees1 * 3600 + minutes1 * 60 + seconds1 - (differenceDegrees * 3600 + degrees2 * 3600)) % 60;
        double differenceMinutes = Math.Floor((differenceDegrees * 3600 + minutes1 * 60 + seconds1 - (differenceDegrees * 3600 + degrees2 * 3600)) / 60);

        // 组装结果
        int roundedDegrees = (int)Math.Round(differenceDegrees);
        string resultFormat = "{0:D2}.{1:D2}.{2:D2}";
        return string.Format(resultFormat, roundedDegrees, differenceMinutes, differenceSeconds);
    }

    private static bool ParseAngle(string input, out double degrees, out double minutes, out double seconds)
    {
        try
        {
            // 使用CultureInfo.InvariantCulture解析角度
            var culture = CultureInfo.InvariantCulture;
            var parts = input.Split('.');
            if (parts.Length != 3)
            {
                throw new FormatException($"Invalid angle format. Expected format: 'X.XX.XX'");
            }

            double.TryParse(parts[0], NumberStyles.Any, culture, out degrees);
            double.TryParse(parts[1] + "." + parts[2], NumberStyles.Float, culture, out double totalSeconds);
            minutes = totalSeconds / 60;
            seconds = totalSeconds % 60;
            return true;
        }
        catch (FormatException)
        {
            degrees = minutes = seconds = 0; // 如果无法解析，设置默认值
            return false;
        }
    }
}

// 调用示例
string angleDifference = AngleHelper.SubtractAngles("180.0000", "90.5000");