This command can be used to input a new centerline or edit an
existing centerline (.CL) file. It is a dialog-based alternative to Design
Centerline
and has the advantage of accepting whatever information you have on
your centerlines (coordinates, stationing, length of tangents and arcs,
etc.). For creating a new centerline, it is ideal for entering data
straight from highway design plans. For editing, this command allows
you to change any of the geometric properties of any of the elements of
the centerline (lines, curves, spiral-only and symmetrical
spiral-curve-spiral elements), including the starting coordinates and
station.
Starting this command launches the Centerline Input-Edit main dialog box. To edit an existing Centerline, you can either pick the Load button and pick the .CL file, or pick the Screen Pick button and pick the polyline in the drawing that represents the Centerline. The Centerline is then displayed in the graphics window of the dialog box. The highlighted segment in the text window is also highlighted in the graphics window.
Up/Down: Moves elements in the table Up and Down in the
list. For example, if this centerline ended with a tangential line from
the last curve, then was followed by a non-tangential line at 45
degrees NE, moving
the last element up would create a line at 45 degrees after the curve
(non-tangential),
and the formerly tangential line will remain tangential and therefore
continue
at NE 45 degrees.
Draw: This button draws the centerline in the drawing on the
specified layer.
Drag Action (Zoom and Pan): In the graphics window, hold the
left mouse button down and move mouse to Pan, roll the wheel to Zoom.
Load: Loads an existing centerline (.CL) file for review or
editing. After loading a centerline, the listbox in the dialog shows a
list of all the elements in the centerline, identifying them as either
a line, curve, spiral only or full spiral-curve-spiral element and
reporting the ending
station, northing and easting of the element.
Add: Adds a new element after the highlighted element. Prompts
you
for the type of the element to be added, Line, Curve, Spiral-Only or
Spiral-Curve-Spiral.
Edit: Allows you to edit the highlighted segment.
Remove: Removes the highlighted element from the centerline.
Assign Point Numbers: This will create Carlson points along the
elements of the centerline and store them to the current CRD file. The
new points will be numbered in sequence beginning with the first
available point number in the CRD file.
Save: Saves the currently loaded centerline to a file, or will
prompt
you for a name if no name has been set.
SaveAs: Prompts you for a file name for the saved file.
Exit: Exits this routine, prompting to save changes if necessary.
Help: Goes to the Help screen for the Input-Edit Centerline
command.
Station Equations: At any number of locations on a centerline,
you can set the back station and forward station for the re-stationing
of
the centerline. The station equation dialog appears below:
If the Station Back is lower than the Station Ahead, then a "gap" is
inserted
in the centerline, where the stations jump forward. If the Station
Ahead is less than the Station Back, then an overlap occurs, where the
common
station range is repeated.
The dialog for every type of element shows the point ID, the northing, easting and station of the start point of the element. It then allows the user to modify or define the parameters specific to the type of element. The following are some of the things to remember about data entry in the centerline editor. These are valid for lines, curves and spirals.
• Wherever length of the element is to be entered, entering an expression of the type 123.5 - 93.7 would evaluate the difference of the values. This is particularly convenient where only the stations of the start and end points of the element are known.The dialog for a Line allows the user to specify the line primarily by its length or station and its bearing. The line can also be defined by its end point number or its coordinates. The bearing of a line can be changed if the Tangential to the Previous Element toggle is not checked. By default, any line which follows a curve element is defaulted to be tangential to it. To use a bearing different than that of the previous element, uncheck this toggle and enter the bearing.
The dialog for the Curve allows the user to define the curve primarily by its radius and delta angle or arc length. The other parameters of the curve that can be edited are the bearing of tangent-out and the "Station to", which also defines the arc length. The curve can also be specified by entering the coordinates or point numbers of its end point (PT) and the radius point. Another way to specify the curve would be to enter the chord length or PT point station and chord bearing. If the central PI point and a point on the forward tangent are known, then the curve can be defined by entering both of these points and at least one other property of the curve (like radius, arc length, delta angle). The point on the forward tangent can be any point that defines the tangent out direction including the next PI point. If only the central PI point is known, then the tangent-out can be entered by bearing instead of by forward tangent point. Central PI and forward tangent points are not displayed from the .CL file. They have to be entered by the user and are valid only for that particular edit session; that is, they are not remembered the next time the file is loaded. Curves are assumed to be tangent to the last element unless the Tangential to the Previous Element checkbox is cleared.
The Curve Edit Mode option defines how the curve is accepted in the centerline. If the Hold PC point is checked on, the radius is taken as fixed and the delta angle of the curve is calculated based on some additional parameter. Hence, the extent of the curve is unlimited. However, if the Hold PI points option is checked on, the bearing of tangent-out of the curve is taken as fixed and the radius is calculated based on some other parameter. In this case, the curve is completely restricted within the central PI point and the bearing of tangent out. Hence, when the Hold PI points option is checked on, the above parameters should also be defined to carry out the calculations.
The dialog for the Spiral-Curve-Spiral element allows the user to define the spiral by entering either the various parameters of the spiral (like the angles and lengths) or the coordinates or point numbers of its defining points: the TS (Tangent-to-Spiral), SC (Spiral-to-Curve), Radius point, CS (Curve-to-Spiral), ST (Spiral-to-Tangent) and end point (optional). While defining the spiral by its geometric properties, the program will accept the data even if the information for the simple curve is given with zero spiral lengths. In this method, however, the central PI point of the spiral MUST be specified (that is, it is always in Hold PI Points mode). The tangent out can be defined by entering bearing or by specifying a point on the forward tangent. This forward tangent point can be the next PI coordinates. The direction of the spiral-in and spiral-out elements would be the same as the direction of the simple curve (left or right).
The spiral can be defined by several different parameters and the
order that you enter data into the spiral dialog can be important.
There are two main sequences for entering data. The method to use
depends on the spiral data that you have. The first method is to enter
the radius of the simple curve, the spiral in and out lengths, the
tangent bearing out and the PI station. The second method is to make a
Line segment coming up to the TS (tangent to spiral) point. This Line
segment should be added before creating the Spiral element. Then with
the Spiral In point set to the TS point, enter the radius of the simple
curve, the spiral in and out lengths, the curve direction
(left or right) and the arc length of the simple curve. Then the rest
of
the spiral points will be calculated.
The Spiral Only element allows for flexible transitions from curve to
spiral
to curve or line to spiral to curve or between any combination of curve
and
line elements. The Spiral-Curve-Spiral element, for example, can be
entered as Line, Spiral Only, Curve, Spiral Only and Line, producing
the
same results.
Once all the elements of the centerline are defined, the file can be saved and then plotted using the Draw Centerline File command.
Example
Here is an example of a highway interchange ramp that involves a
starting tangent and a spiral curve that goes abruptly into a simple
curve and then a final tangent. Here is the starting dialog.
You start by entering a starting Northing and Easting and starting
Station. The Start Point# is optional. Then the concept is that you
click Add to add each subsequent element (line, curve,
spiral-curve-spiral or spiral only).
Line (Tangent) Segment: We want to enter the tangent segment length up to the TS (tangent to spiral). Enter in the length (200.0), bearing (88.0732) and then the bearing quadrant (NW). Since the next spiral-curve-spiral element can be based on a PI station, it is not necessary for this line segment to go up to the TS point. The purpose of this line segment is to establish the tangent-in direction.
When OK is clicked, the routine will add the Line element as the first in the list of complete centerline elements. Next up is Curve-Spiral-Curve. Click Add.
Spiral Segment: Though the dialog is complex (for total flexibility), the key on a typical symmetrical spiral curve is to enter four things: (1) the radius of the simple curve, (2) the spiral in and out lengths, (3) the tangent-out bearing and (4) the PI station (1835.67). Everything else will calculate when you press Enter for the PI station.
Curve Segment: Add the next element and select curve. The Curve dialog appears. The key is to enter the Radius Length (255), the Arc Length (150) and the Curve Direction. Everything else will calculate.
Final Line Segment: All you need to enter in the final dialog for the line (tangent) segment is its length. All other items will calculate when you press Enter.
The completed centerline will appear as shown in the dialog and each element can be edited. Pick the Save button to store this centerline data to a .CL file.
Pulldown Menu Location: Centerline
Keyboard Command: cledit
Prerequisite: A CRD file to put points or take points from
File Name: \lsp\eworks.arx