static string MakeRelativePath(string absolutePath, string pivotFolder)
{
    //string folder = Path.IsPathRooted(pivotFolder)
    //    ? pivotFolder : Path.GetFullPath(pivotFolder);
    string folder = pivotFolder;
    Uri pathUri = new Uri(absolutePath);
    // Folders must end in a slash
    if (!folder.EndsWith(Path.DirectorySeparatorChar.ToString()))
    {
        folder += Path.DirectorySeparatorChar;
    }
    Uri folderUri = new Uri(folder);
    Uri relativeUri = folderUri.MakeRelativeUri(pathUri);
    return Uri.UnescapeDataString(
        relativeUri.ToString().Replace('/', Path.DirectorySeparatorChar));
}