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                 When you remove track points (either manually or by applying some filters), 
                they are still kept in the track but marked as filtered. If View | 
                Filtered points is on, those points are gray in the Points list 
                and the adjacent edges are displayed as black dash-dot lines. 
                If a filtered point seems to be good, it can be restored back. If you 
                are sure that all filtered points are invalid,  you can completely delete 
                them all by choosing  Filter | Delete filtered points. 
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