Image_Graph_Common | --Image_Graph_Element | --Image_Graph_Plotarea_Element | --Image_Graph_Marker | --Image_Graph_Marker_Pointing
Points to the data using another marker (as start and/or end)
Image_Graph_Marker_Pointing Image_Graph_Marker_Pointing( int $deltaX, int $deltaY, Marker &$markerEnd)
void setMarkerStart( Marker &$markerStart)