ACA: AEC Modify Tools, Part 5, AEC Obscure

First post in series [AecLineworkExtend].
Previous post in series [AECLineworkSubtract].

The AecLineworkObscure command can be found on the Home ribbon tab, on the Modify panel flyout, by selecting the Obscure tool from the Obscure/Crop flyout. If the Obscure tool is not the displayed tool on the Obscure/Crop flyout, select the right side of the split button (down arrow icon) to deploy the flyout and choose the Obscure tool. Or, with no command active, you can right click in the drawing window, and choose AEC Modify Tools > Obscure from the context menu.

The AecLineworkObscure command is used to change the parts of linework, AEC Polygons, Mass Element Extrusions that have an embedded profile, Spaces and Hatches as well as Block References which contain any of these objects that fall within a user-defined obscuration area, replacing the linework or boundaries of the other items with linework placed on the layer defined by the HIDDEN Layer Key in the current Layer Key Style. This layer typically has a dashed linetype assigned. In the out-of-the-box Imperial content, using the AEC Title Case - NCS 256 Color Layer Key Style, this layer is G-Detl-Hidd, color Red and linetype HIDDEN2.

As with the AecLineworkSubtract command, there are two options for specifying the extents of the obscuration area:

• Select one or more items in the drawing, which form at least one closed loop. Any single closed item will work (closed Polyline, Circle, Ellipse, AEC Polygon, Mass Element or Space), as will any combination of objects that, combined, form at least one closed loop.
• Press the ENTER key when prompted to select items to be obscured, and then define an obscuration rectangle by selecting opposite corners of a rectangle. The rectangle will have sides parallel to the X- and Y-axes of the current UCS.

The primary use of this command is to make it easy to show parts of Detail Components that, for the detail at hand, occur behind another item, with a hidden linetype, without having to explode or manually break linework. It will work on linework and block references generated by other means.
Here are some additional notes regarding the AecLineworkObscure command:

• MText, Text, Ellipses and Ellipse Arcs cannot be added to the selection set of objects to be obscured.
• Ellipses and Ellipse Arcs can be selected as (part of) a boundary defining the area to be obscured.
• Mass Elements with a shape other than "Extrusion" and Mass Element Extrusions that have an external Profile can be selected as objects to be obscured, but will not affected by the AecLineworkObscure command. These types of Mass Elements can be used to define the area to be obscured.
• If a Block Reference is selected as an object to be obscured, only those nested objects within the block on which the AecLineworkObscure command works will be affected.
• Attributes within a Block Reference will not be affected by the AecLineworkObscure command.
• If a Block Reference is selected as an object to be obscured, it has obuscurable nested elements and it is the only instance of that Block Reference in the drawing, then the original block definition will be redefined to include the effects of the obscuration. If at least one instance of the Block Reference remains unaffected by the obscuration, then the original block definition will remain unchanged and the affected instance(s) will become instance(s) of new, anonymous block definition(s).
• Multi-View Blocks can be selected as an object to have a part obscured, but will not be affected by the command.
• If the active View Block of a Multi-View Block contains linework that forms a closed boundary or contributes to a closed boundary, it can used to define the area to be obscured.
• Unlike the AecLineworkTrim, AecLineworkDivide and AecLineworkSubtract commands, use of the AecLineworkObscure command on a closed Polyline or Circle does not result in one or more closed Polylines.
• A Line or Arc, freestanding or within a block reference, that is in the selection set of the AecLineworkObscure command is replaced with one or more Polylines.
• A Circle, freestanding or within a block reference, that is in the selection set of the AecLineworkObscure command is replaced with one or more Polylines for the portion(s) outside of the area being obscured and one or more Arcs for the portion(s) within the area being obscured. The Polyline(s) and/or Arcs will have vertices/endpoints at the World Coordinate System 0-degree and 180-degree locations on the original Circle.
• A closed Polyline, freestanding or within a block reference, that is in the selection set of the AecLineworkObscure command is replaced with one or more Polylines for the portion(s) outside of the area being obscured and Lines/Arcs for the portion(s) within the area being obscured.
• An open Polyline, freestanding or within a block reference, that is in the selection set of the AecLineworkObscure command is replaced with one or more Polylines for all portions, whether within or outside of the area being obscured.
• If a hatch object is to be obscured, the hatch will be removed from the from the obscuration area, but no hidden graphics will be generated.
• Obscuring an associative Hatch will result in a non-associative Hatch, regardless of whether or not the boundary of the Hatch is included in the obscuration.
• Associative Spaces, Walls, Doors, Windows and Door/Window Assemblies can be selected as items to be obscured, but will not be affected by the command. Non-associative Spaces do work with the AecLineworkObscure command.
• If you obscure an AEC Polygon, the Exterior Edge components of the AEC Polygon that fall with in the obscuration area will be replaced with "hidden" lines or arcs. Interior Edge components of the AEC Polygon, if present, are removed, but not replaced with "hidden" linework. New Exterior Edges and, if present, Interior Edges are created when the AEC Polygon extends beyond the obscuration area, but these new edges are "invisible" - no linework is drawn on screen. If Interior or Exterior Hatch or Fill components are turned on, they will, however, change to fill in the modified AEC Polygon extents, which does not give a true obscuration effect.
  
• If the area to be obscured effectively splits an object into two or more separate pieces, the result depends upon the selected object. Hatches, Mass Element Extrusions (embedded Profiles), AEC Polygons and Spaces will result in one object, with two (or more) separate, non-contiguous regions. See above for note on how new AEC Polygon Edges will not have any visible graphics.
• If an object (or nested object, in the case of a block reference) in the obscure selection set is entirely within the obscuration boundary, it will be completely replaced with hidden linework.
• Unlike the AecLineworkSubtract command, if you select one or more objects to define the extents to be obscured, you are not prompted as to whether the boundary objects are to be erased.
• Even though Mass Element Extrusions (with embedded profile) are 3D objects and Spaces can be 3D objects, the hidden linework is only 2D, in the current X-Y plane. The removal of portion of these objects in the obscuration area does affect the object in 3D.

As with the AecLineworkDivide and AecLineworkSubtract commands, there are object types and combinations of objects within a Block Reference that I did not test. If you are thinking of using the AecLineworkObscure command in a situation that you have not previously encountered, you may want to use the Mark option of the UNDO command to place one or more UNDO Marks prior to using the command, so that you can easily UNDO Back to the point before the command was used if you get unexpected results.

Next post in series [AECLineworkMerge]