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It defines the command MidPoly which does the trick. I mean a small program which goes through all the segments and calculates the distances and then finds the midpoint along the pline. Credits : For Dimention Technologies 

How to replace selected points in a drawing with a defined block in the drawing ? This routine could be more rubust but it is still helpful. It does let you specify the scale of the block and rotation. Command : PT2BLOCK Enter the name of the block that will replace the point objects with ,enter> Specify the insertion Scale Factor Specify the rotation angle Select Point objects that will be replaced by the block. Note: this is not a global point replacement program by default. If you would like to replace all point objects, enter ALL at the command line. Credits :                  Michael Weaver,                           2175 George Road                       Fairbanks, Alaska 99712                     (907)488-3577 voice and fax                   Email:71461.1775@compuserve.com                  Mike_Weaver_Alascad@compuserve.com                            Fri 02-23-1996                           (c)1996 Alascad