How to identify polylines within polylines using AutoCAD Automation and Delphi 5?

Hello dear Newsgroup Readers,

Currently, I am working on a Borland Delphi 5 program that is able to
retrieve information from an AutoCAD drawing and store it in a
database.

More specifically: each AutoCAD-drawing (in AutoCAD 2000i/20002
format) represents a floor in a big building. Polylines are drawn on
various layers and each polyline defines a room on the floor. In the
database, I store information about the polyline (room), like the
perimeter and area attributes. The "link" which allows the Delphi
Program to "talk" to AutoCAD and send AutoCAD-commands is realised by
an ActiveX Automation OLE-object.

Retrieving information like perimeter and area for a room works just
fine and is not so difficult, however, now I have some nasty
occurrences of polylines in the AutoCAD drawing: WITHIN the polyline,
other (smaller) polylines are present. You can look at these smaller
polylines as pillars or concrete columns within the room. These
polylines are drawn on the same layer as the room-polyline.

Off course, these pillars have an area of their own. The area values
of all the pillars-polylines in a room must be subtracted from the
area of the complete room, and so calculates the "real" area of the
room. There is not a ready-to-use AutoCAD-function present to
accomplish this, so I must do this manually. :-(

In short, I am looking for a way to identify pillar-polylines within
the room-polyline. I have to do this for every room-polyline there is
in a drawing. When I can get a list somehow of all the polylines
(handles) within the room-polyline, I can calculate a total amount of
area which must be subtracted from the total area of the room.

Does anybody have any clue on how I could handle this problem with the
use of Delphi and the AutoCAD Autmation object?

Many thanks for answers!

Rene Guillot