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Through Visibility (v8i)

Through Visibility is used to evaluate visibility along a road using plan, profile, cross section and perspective views simultaneously.  Evaluate either existing sight conditions or proposed design work.  If evaluating a proposed design, then it is recommended to generate a Composite Model of the proposed design into the existing detail.

Through Visibility is located in MX, from the Analysis menu, select Visibility > Through Visibility...


Reference Details

The Through Visibility: Reference Details panel has four tabs grouping the visibility details needed for analysis:

  1. Model Details
  2. Visibility Details
  3. Objects
  4. Display

                        Through Visibility Model Details tab

The Model Details tab is used to specify the reference and analysis model details.

If Eye and Target Control Strings list boxes are left blank, then the eye and target offsets will be measured from the reference string.  The Offset of Section adjusts the cross section extents from the reference string.  Select the Side of Road to Drive on.

                        Visibility Details tab

The Visibility Details tab is used to specify the Sight Distance Required, Eye Point Details, and Target Point Details.

For the Sight Distance Required, select Specified.

Eye and target offsets are measured differently depending on whether or not the Control Strings are specified on the Model Details tab.  If no Eye and Target Control Strings are specified, then the eye and target offsets are measured from the reference string.  As usual, positive offsets are measured to the right, negative to the left.  If Eye and Target Control Strings are specified on the Model Details tab, then positive offsets are measured from the control string towards the reference string, negative offsets go away from the reference string.

There are two Types of Analysis used to determine visibility:

  1. Line of Sight  This analysis uses a single vector from the eye point directly to the target point.  If the vector does not intersect the surface (or any defined objects), then the required sight distance is achieved and the entire vector is displayed in the Visible color (yellow by default).  If the vector intersects the surface (or any defined objects), then the required sight distance is not achieved and non-visible part of the vector is displayed in the Invisible color (red by default).
  2. Shadow  This analysis uses multiple vectors from the eye point to points on the surface which lie between the eye and the target point.  These vectors increase in grade as they progress from the eye point and the target point.  If the grade of any vector is less than the previous visible vector, then that point is deemed to be shadowed from the eye point.  These shadowed points are projected onto the Line of Sight vector and displayed in the Invisible color.

When using the Shadow type of analysis, there is a choice to Check Against the Surface or the Target Height.   The Surface analysis shows when the surface is blocked by a surface or an obstacle.  The Target Height analysis shows when the target is blocked by a surface or an obstacle.

Check the Move Target to Achieve Visibility box in order to relocate the target point to a position where maximum visibility is achieved (purpose unclear).

                        Objects tab

Since the typical string model reflects the surface location of detail, it is often necessary to compliment the analysis model with visible objects.  The Objects tab is used to create simple, temporary objects to analyze their effect on visibility.

Existing strings can be assigned a Height, Width, and an Offset for any part of the string.  These objects can be saved in a file for future use.

                        Display tab

The Display tab is used to control the window's display and colors.

The Display Envelope delineates the limits of visibility.   The Display Envelope is only shown on the MX Display in the color magenta.  The Display Construction Lines shows all the sight lines used to generate the Display Envelope.

All the information in the Visibility Details, Objects, and Display tabs are adjustable from the Through Visibility panel.  Select Next to advance to the Through Visibility panel.


The Through Visibility Panel

The Through Visibility panel graphically presents visibility sight lines with the use of several interchangeable widows.  The windows types available are Cross Section, Profile, Perspective, and Report.  The MX Display is also synchronized with the Through Visibility panel for the plan view evaluation.

Each window offers a toolbar, many options on the toolbar are similar across all windows.  All adjustments made with these options are automatically seen in the Through Visibility windows.  These options are:

  • Standard MicroStation view controls
  • Vertical Exaggeration
  • Create Video  For the perspective window.
  • Display  This controls the same options found on the Display tab of the reference details panel.
  • Visibility Details  This controls the same options found on the Visibility Details tab of the reference details panel.
  • Windows  To select a different window type.
  • Minimize/Maximize  To minimize/maximize the window to the Visibility Viewer panel.

There are also controls at the bottom of the Visibility Viewer.  They are:

  • < Back  Returns to the reference details panel.
  • Tracking  This locks the sight line to the cursor for "real time" control of the sight line, the cursor must be in the plan view to take control.  Tracking can also be toggled on and off with the right mouse button.
  • Look Forward/Look Reverse  To toggle between the forward direction analysis and the reverse direction analysis.  When switching directions, the eye and target positions also change to the other side of the center line.
  • Station Selector  Is used to step through the sections, or alternatively select a station from the pulldown list.
  • Objects...  This controls the same options described on the Objects tab of the reference details panel.
  • Save  Saves the current settings.  Saves the envelope and visibility construction strings to a specified model.
  • Finish  To exit Through Visibility.

The Viewer Windows

Cross Section View window

The Cross Section window shows the current Eye Point cross section and corresponding Target Point cross section for the required sight distance.  The Station of each point is displayed at the bottom of each section.  Crosses show the location of both the Eye Point and the Target Point.  Dots on the cross sections show the location of reference model strings used to generate each cross section.  Placing the cursor near any these dots will trigger a tooltip window reporting that string's details.  If the required sight distance is not achieved, then the target symbol will appear in the invisible color (red by default).

Profile View window

The Profile window displays the profile of the sight line and the collinear profile of the analysis model.  The top of the widow displays the required and achieved sight distances.  If the required sight distance is not achieved, then the non-visible portion of the sight line will appear in the invisible color (red by default).  When using the Shadow analysis, all shadowed regions will appear in the invisible color.

Perspective View window

The Perspective window shows the current perspective view.  The Display button controls the display of the triangulation, the working cross sections, and the clipping of model information beyond the target.  The top of the widow displays the required and achieved sight distances.  If the required sight distance is not achieved, then the target symbol will appear in the invisible color (red by default).  The Perspective window toolbar also includes a button to Create Video.

Report window

The Report window presents the associated data.  The Report window toolbar includes buttons to Save Report, Print report, and add an Output Header.

MX Display window

The MX Display shows the sight lines in plan view.

To show the visibility envelope and/or the envelope construction lines, select any of the Display buttons from the Visibility Viewer.  If the required sight distance is not achieved, then the non-visible portion of the sight line will appear in the invisible color (red by default).  When using the Shadow analysis, all shadowed regions will appear in the invisible color.

Select Finish to exit Through Visibility.

 


Related Pages

MX Add-In Index

MX Wizard Index

MX Macro Index

MicroStation v8 Program Index





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