 DROP                                                                Menu: SCRN
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 Drops from the model all entities not included within a specified fence.

         1. (POINT) first corner of fence
         2. (POINT) opposite corner of fence
         3. (Y/N) confirm deletion of the selection group <n>
      if reply is `n':
         4. ! correct the selection group, use \sdel to delete it.

 Description:
 This command clears your file of those entities that are outside a specified
 fence.
 Pick the first corner of the fence, and then the opposite corner.
 Any entity with one or more points outside the fence, and any instance (placed
 object) whose reference point is outside the fence, will be indicated as
 selected entities. You are asked to confirm that the selection is as intended.
 If you reply positively all the selected entities will be deleted from the
 model. The display will be refreshed.
 This command is useful if objects have been wrongly placed. The command should
 be executed only while in an orthogonal projection.

         Example: \drop -10 -10 0 10 10 0 y

 Result: Any entity having one or more points outside the defined fence
 (-10 -10 0, 10 -10 0, 10 10 0, 10 -10 0), and any instance (placed object)
 whose reference point is not within the fence, is deleted from the model.
