[Therion] scrap in multiple parts

Hello everybody... I've got the following problem : I've made a survey (in a ptolemaic cistern, in Alexandria) and my plan is, on the sketch, in multiple parts : each time I've change the direction, I've made a new part, without any link (problem of angle between both parts, that I can't report precisely). How can I do ? I've tried to put every parts on the same scan and to precise for each the 2 survey points, but the result isn't very good... Do I have to join all parts (with the right angles...) before drawing it with the map editor ? Is there another way to do this ? Thank you very much Thierry