Regression Point Properties

  • Feature Definition/Name/Description: Name, assigned feature and description of the point.
  • X, Y, Elevation: Coordinates and elevation of the point.
  • Slew: Horizontal Slew (offset). Value is signed, negative means to the Left.
  • Lift/Lower: Vertical Slew (offset). Value is signed, negative means Lower.
  • Cant: Design cant value on the point location.
  • Existing Cant: Existing cant value on the point location. Only available if points are regression line is created from rails.
  • Instantaneous Radius: Instantaneous Radius on the point location. This is calculated by fitting a 3 point arc on the selected, previous and next points.
  • Weight: Defines the significance of the point during regression analysis. Points with greater weight "pull" the regressed element more strongly than do points with lesser weight. Weight is a unitless value.
  • Status:
    • Fixed: assigns a weight of 1000. A weight of 1000 designates the point as extremely significant, particularly compared to Normal points, which are assigned a weight of only 0.01 (again, the 0.01 can be globally modified).
    • Normal: assigns a weight of 0.01 (although this value can be globally modified). Most points are assigned a Normal status. All points with a weight of 0.01 are equally significant; however, they are far less significant than Fixed points, which are given a weight of 1000.
    • Ignored: excludes the point from consideration during regression analysis but still includes the point in reporting. This option allows you to keep track of a point (perhaps for grading purposes) but prevents the point from skewing the regression analysis. Points marked as Ignored are not assigned a Weight.
    • Information Point: These points are not used in regression analysis but used for information display but used for display of slew values.

  • Offset: specifies an offset from the regressed element. Offsets can be applied to either Fixed or Normal points. An offset allows you to incorporate a point in regression analysis even if the point lies offset from the alignment such as a platform edge. For example, if you know that a surveyed point should lie exactly 5 meters to the left of the centerline, you could assign it an offset of -5.0. Regression analysis would then be able use this point in positioning the alignment. Rather than running the alignment directly through the point, regression analysis would attempt to run the alignment 5 meters to the right of the offset point.

    The following diagram shows a set of points to be regressed. The offset point is located away from the other points. When the offset is factored in, regression analysis knows that the regressed element should not pass directly through the point because the point is offset from the intended path of the element. The point shown with a red outline represents the point that will "pull" the regressed element. It is through this imaginary point that the element will seek to pass.

  • Unacceptable Slew Left/Right: Unacceptable slew values for the point. These values can be set while creating the geometry using single horizontal regression command or with Single Element Nudge tool. They can also be updated using point table. Values are used for slew highlighting.
  • Maximum Lift/Lower: Maximum Lift Lower (vertical slew) for of vertical points. These values can be set while creating the geometry using single vertical regression command or with Single Element Nudge tool. They can also be updated using point table. Values are used for slew highlighting.
  • Geometry/Geometry Type: Geometry element that is present on the selected point location. Type of that geometry; line, arc, spiral. When there is an arc radius is also displayed.