[Therion] Plan only walls and centerline

Hi, I`am sure it is possible with Therion to get a plan without any speleothemes. The plan is ready drawn, but I need a plan only with walls and pillars and the centerline but without any other drawings. I have searched in the Wiki but without success. Please give me some help. I cannot believe, that I must delete all previously drawn things in the *.th2-File. regards Markus