GetRelativePath

/// <summary>
        /// Returns a relative path string from a full path.
        /// </summary>
        /// <param name="FullPath">The path to convert. Can be either a file or a directory</param>
        /// <param name="BasePath">The base path to truncate to and replace</param>
        /// <returns>
        /// Lower case string of the relative path. If path is a directory it's returned without a backslash at the end.
        ///
        /// Examples of returned values:
        ///  .\test.txt, ..\test.txt, ..\..\..\test.txt, ., ..
        /// </returns>
        public static string GetRelativePath(string FullPath, string BasePath)
        {
            // *** Start by normalizing paths
            FullPath = FullPath.ToLower();
            BasePath = BasePath.ToLower();

            if (BasePath.EndsWith("\\"))
                BasePath = BasePath.Substring(0, BasePath.Length - 1);
            if (FullPath.EndsWith("\\"))
                FullPath = FullPath.Substring(0, FullPath.Length - 1);

            // *** First check for full path
            if ((FullPath + "\\").IndexOf(BasePath + "\\") > -1)
                return FullPath.Replace(BasePath, ".");

            // *** Now parse backwards
            string BackDirs = "";
            string PartialPath = BasePath;
            int Index = PartialPath.LastIndexOf("\\");
            while (Index > 0)
            {
                // *** Strip path step string to last backslash
                PartialPath = PartialPath.Substring(0, Index);

                // *** Add another step backwards to our pass replacement
                BackDirs = BackDirs + "..\\";

                // *** Check for a matching path
                if (FullPath.IndexOf(PartialPath) > -1)
                {
                    if (FullPath == PartialPath)
                        // *** We're dealing with a full Directory match and need to replace it all
                        return FullPath.Replace(PartialPath, BackDirs.Substring(0, BackDirs.Length - 1));
                    else
                        // *** We're dealing with a file or a start path
                        return FullPath.Replace(PartialPath + (FullPath == PartialPath ? "" : "\\"), BackDirs);
                }
                Index = PartialPath.LastIndexOf("\\", PartialPath.Length - 1);
            }

            return FullPath;
        }