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					                MICROSTATION LEVELS AND AUTOCAD LAYERS

The Microstation V8 level system is much different than in previous
version of the software and is more similar to the AutoCAD Layers
approach in order to facilitate file sharing. There are still some
differences worth discussing and the details of View Display versus
Global display of Levels is among them. In AutoCAD, there is only Global
Layer display, which means that whatever settings are active in the Layers
dialog apply to every viewport and sheet in the file. Microstation provides
the option to use either View Display or Global Display for Levels. This
means that the display, freeze, and other level settings are applied either
as View Attributes that affect only the selected view or Level Attributes
that affect all views in the file. In general, View Display of Levels is
incompatible with AutoCAD and only one configuration of Level display
settings can be saved to DWG. This setting is chosen in the DWG Options
of the Save As... dialog under the General tab.


Another notable difference between the Level/Layer systems in the two
programs is the available method for freezing data on a given Level.
While working in DGN mode, only Global freezing of data is allowed by
using the Level Manager dialog - i.e. levels can not be frozen per view.
However, in DWG workmode there are options within the Level Display
dialog that allow for freezing certain views or setting globally frozen
levels, similar to when using the Level Manager. Also, in DWG workmode
the View Display option is not available in the Level Display dialog
because this level display method is incompatible with AutoCAD, as
stated above.


By now it is obvious that in Microstation there are two places where level
display can be controlled - in the Level Display dialog and in the Level
Manager. Note that Global settings in the Level Display dialog are
synchronous with the settings in the Level Manager - changing Global
display or Global freeze settings in one of these places is the same as
changing them in the other and will appear in both places. However, View
display can only be set in Level Display it is a view-based attribute and
can not be set in the Level Manager. In AutoCAD, there is only one place
for layer display settings and that is in the Layer Properties Manager. The
following table illustrates the analogous commands between V8 and
AutoCAD. Keep in mind that the Global settings could also be arrived at
by using the Level Manager in V8, as noted above.



  V8 LEVEL DISPLAY Analogous AutoCAD Layer                    NOTES
     Dialog Mode:       Display Option (Layer
                        Properties Manager Setting)



  Global Display        On/Off


                                                       Not allowed in
  View Display          None                           DWG workmode



  Global Freeze         Freeze in all Viewports


                                                       V8 Viewport Freeze
                                                       will not work with
                                                       data contained in a
  Viewport Freeze       Current Viewport Freeze        Reference - also,
                                                       no V8 analogy for
                                                       freezing in New
                                                       (future) Viewports



Finally, there is also a difference in labeling convention for levels/layers
because Microstation allows both naming and numbering whereas
AutoCAD uses only names. When a DGN file is Saved to DWG, only the
Level names will translate and numbers will be lost, and there are no level
numbers at all in DWG workmode - only names.
EXAMPLES

(1) How should the Levels and Level display be configured in a DGN file
that will be Saved to DWG?


    First, remember that only level names and not numbers should be
       used because numbers will not translate to DWG


    Use Global display settings to control visibility of objects rather
       than using View Display in the Level Display dialog
   



(2) Specifically, how can I handle data that must be frozen in a sheet
viewport only and not in the main model?


    If the original file is in DGN format, drawing views are most likely
       set up in a sheet model using referenced data. If this is the case,
       then the only way to freeze the data in a V8 DGN would be to use
       the Merge into Master command to copy the objects into the
       current file. Once exported to DWG, the data would still be
       individual objects instead of contained in a viewport but the data
       could be unfrozen and refrozen as needed.


    If working in an existing DWG file, there is a Mode selection in the
       Level Display dialog for Viewport Freeze. However, this also will not
       work on data contained within a Reference - only Global freeze will
       work in that case but then data is also frozen in the main model.


EXAMPLE -

				
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posted:7/27/2011
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