Monday, October 22, 2007

Hidden Lines: Explained By Autodesk's Kyle Bernhardt

With the release of ABS 2007, what were previously called Haloed Lines have been globally renamed to Hidden Lines globally across the product. For those running a version below ABS 2006, replacereferences to Hidden Lines with Haloed Lines.

Hidden Line Routine
The Hidden Line routine determines what portions of ABS objects will need to have the Hidden appearance, due to other ABS objects being located above them. These portions of the ABS object deemed to be “hidden” are then assigned to the “hidden” Display Components. This allows for complete control of the Hidden Line Layer, Color, Linetype, Lineweight, and LT Scale in the program.

Fig 1 – Hidden Display Components

These settings are typically defined by the Layer assigned to the Hidden Display Components. The remaining Hidden Display Component properties are set to BYLAYER, which maps them to the Layer’s properties. Assigning the same Layer to the Hidden Display Components of all ABS objects allows for one layer to control the display of Hidden Lines throughout an entire drawing. In this scenario, modification of something like the Color of the Hidden Line Layer will propagate to all Hidden Lines.

Control of Hidden Line Display
The item that controls whether Hidden Lines are used for a particular ABS object type is the Display Representation (DR) that’s used to display that object in the current viewport. The Display Representation that’s used is controlled by the current Display Configuration. See the diagram below for illustration of this fact.

Fig 2 – Display Representation Assignment

For ABS Objects, the Plan Display Representation utilizes the Hidden Line feature. In previous versions the HaloedLine Display Representation utilized the Hidden Lines feature.

If you wanted to create a Display Configuration that does not utilize the Hidden Lines feature, you would associate that Display Configuration with a Display Set which does not assign the Plan Display Representation to ABS objects. You will most likely use the 2 Line Display Representation instead, which displays objects in the same way as the Plan Display Representation, without Hidden Lines. The MEP Basic 2-Line DC, which is contained in the default ABS template, is a good example of such a Display Configuration.

Hidden Line Gaps
The Hidden Line routine also has the ability to apply a gap in the display of an ABS object when the routine detects that a portion of that object is hidden by an object above. See the figure below to illustrate this feature.

Fig 3 – Hidden Line Gaps

This feature produces a visual effect that complies with some existing drafting standards, and is a desired effect for the production of Construction Documents.

This is a drawing-specific setting, and is controlled in the ABS Crossed Objects tab of the Options dialog, see below.

Fig 4 – Hidden Line Gap Settings

Enabling this feature will result in an additional calculation added to the Hidden Line Routine.

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