Standards
This dialog box is used to enter the vertical alignment specifications.
These controls modify the entire output alignment.
Aligment Specification
Curve type (Drop List)
Select the type of curves you would like to generate. The options and controls in the Alignment Specifications area vary with this selection.
PolyLine selection
This will generate an alignment with straight segments only (no curves).
Curves [Fast] selection
Generate an alignment with curves where tangents are not required between curves.
Curves and tangents [Slow] selection
Generate an alignment where a tangent is inserted between curves. With this choice, the resolution time can be significantly slower.
Variable curves and tangents [Slowest] selection
Similar to Curves and tangents [Slow] but curve, tangent and base length can vary. With this choice, the resolution time is the slowest.
User defined selection
Preserves the location and length of the cuves and tangents as defined in the Reference alignment. Similar in speed to Curves [Fast].
Heuristic shortcut (Check Box, Edit Box)
Only available when Curves and tangents [Slow] or Variable curves and tangents [Slowest] is selected.
This option can reduce the resolution time, however, optimality is not guaranteed anymore. The parameter defines the allowed average deviation from a theoretical lowest cost reference alignment. The cost of this reference alignment is reported in the log (minimum cost estimate); the cost of the optimal solution (Heuristic shortcut un-checked) will be near to, but greater than, this cost.
Maximum grade break (%) (Check Box, Edit Box)
Only available when User defined is selected.
If checked, enter the maximum grade break allowed between two consecutive straight segments. Otherwise unconstrained.
Min. curve length (Check Box and Edit Box or Edit Box only)
Only available when Curves [Fast], Curves and tangents [Slow], or Variable curves and tangents [Slowest] is selected.
For Curves [Fast] or Curves and tangents [Slow], check to be able to set the minimum curve length; otherwise unconstrained. For Variable curves and tangents [Slowest], the minimum curve length must be provided.
Min. tangent length (Check Box and Edit Box or Edit Box only)
Only available for edit when Polyline or Variable curves and tangents [Slowest] is selected.
When Polyline is selected, check to set the segment length; otherwise unconstrained. When Curves [Fast] is selected, the minimum tangent length is set to 0. When Curves and tangents [Slow] is selected, the minimum tangent length is set equal to the minimum curve length. When Variable curves and tangents [Slowest] is selected, you must provide a value for the minimum tangent length.
Base length (Edit Box)/Accuracy (Slider)
Only available when Variable curves and tangents [Slowest] is selected.
The base length represents the smallest segment length that will be used in the alignment optimization; curves and tangents will be a multiple of this length. It must be less than or equal to the minimum curve length and the minimum tangent length. Its value is controlled using the slider Accuracy or by entering a value between 1 and 5 in the edit box to the right of the slider. A smaller base length will give better results but the resolution time may increase significantly.
Note: the base length should be greater than the spacing between stations, otherwise, unnecessary curves may appear.
Min. tangent grade (Check Box)
Set this check box and enter the smallest desired grade (absolute value); this will prevent tangents at or near zero grade.
Note: this constraint might slow down the resolution process.
Include Ctrl Pts/Ranges for curve definition (Check Box)
Set this check box to reduce the probability of an infeasible situation caused by curves near control points. Setting this check box also ensures that the range constraints as defined will be used, otherwise the safest constraints are considered, i.e., if a curve or a segment overlaps a range, the safest constraints are used.
Note that this option can introduce tangents/curves that are shorter than the desired minimum.
Range Constraints
These controls modify specified station ranges of the output alignment.
Fill in all desired values then press Add/Edit to update interval list. Select a list item to populate controls with values from the selected interval.
Note: to remove an interval you need to overwrite it with another interval.
Grade (%): Minimum, Maximum (Edit Boxes)
Enter the minimum/maximum grade values in %.
Curvature (Minimum K) or Maximum grade break (%): Sag, Crest (Edit Boxes)
When Polyline is selected, this group is entitled Maximum grade break (%), otherwise it is Curvature (Minimum K)
For curves, recall that K is defined as the length of curve required to change grade by one percent. Sag/Crest of the alignment will be constrained to be greater than the specified K (or grade break) over the selected range. If K is 0 (or the field is blank) the curvature will be unconstrained.
For Polyline, it is possible to set the maximum grade break. Inf indicates that the grade break is unconstrained.
Linear/Set (Check box)
For curves, if Linear is set, the alignment will be constrained to be a tangent (no curve) over the selected range.
For Polyline, check Set to be able to set a maximum grade breaks.
Interval: From Stn., To Stn. (Edit Boxes)
Interval station range. From Stn. ".." means start of alignment. To Stn. ".." means end of alignment.
Add/Edit (Button)
After entering or modifying all the controls to the left, press the Add/Edit button to update the list.
Note: you must press this button to accept changes.
Ranges (List)
This list displays all defined intervals and their constraint values. Select a range to populate the controls above with it's contents.
