The string identifiers and labels come from the strings that the triangulation is made from. this data is presumably not part of your surveyors data, and you are not going to be able to 'make it up'.
What type of data are you given? Would it not be easier to use the data you are given (presumably triangle edges) as 'strings', and then triangulate that?
What type of data are you given? Would it not be easier to use the data you are given (presumably triangle edges) as 'strings', and then triangulate that?