const string str = @"57° 1' 50.031";
var mask = @"^([0-8]?[0-9]|90)°(\s[0-5]?[0-9]')?(\s[0-5]?[0-9](,[0-9])?"")?$";
var degress = Regex.Matches(str, mask).Cast<Match>().ToArray();