Horizontal Curves

Displaying Curve Data

To display curve data in the Traverse View, include the letters R (radius), C (arc length), Q (delta or central angle), c (PC->PR bearing), r (PR->PT bearing) and t (tangent) in the display sequence. Include the letters H (horizontal distance = chord dist) and A or B (chord azimuth or bearing) if they are not already included.

Note: For a curve or spiral segment, the dist and bearing or azimuth displayed in the Traverse View are the dist and bearing or azimuth of the long chord.

Grid vs Ground or Geodetic

Distances that are part of a curve are both entered and displayed based on the distance type of the traverse. So if the traverse is displaying 'ground distance at project elevation (3500 ft)', curve data like radius, arc length and tangent length will be displayed as 'ground distance at project elevation (3500 ft)'.

TPC stores the values you enter as raw data. So if you enter a radius of 500', TPC stores 500' as the radius. However, the radius, along with any other raw curve distances, is converted to a grid distance for any internal computations. Spirals do this same thing also.

Curve Data is Stored with the PT

All curve data is stored with the PT of the curve. To edit a curve, highlight it's PT and choose COGO | Horizontal Curve or just edit any of the curve data in the same row as the PT.

Enter Curve Data for Existing Lines

Sometimes you want to specify curve information for an existing line (chord). This is typical of deed descriptions that call the bearing and distance of the chord, plus the radius and direction (clockwise or counter clockwise) of the curve.

The Traverse View will display PC and PT in the Type column indicating the Point of Curvature and Point of Tangency.

If you include other curve columns in the display sequence, TPC will compute the other curve parameters and display them for you.

Note: In this situation, TPC may not store the curve data you entered as raw data for that traverse point. Instead, TPC will compute the corresponding grid radius for the curve and store it with the line from the PC to the PT. Raw curve data is only stored with a traverse point if that data is used to compute the PT of the curve.

Creating Curves as You Go

You can also enter curves as you go, creating the PT position and curves together.


If you include other curve columns in the display sequence, TPC will compute the other curve parameters and will display them for you.

Raw Data

If you enter enough raw data (radius, delta, etc) for TPC to compute the curve, TPC will store the raw data. TPC is then free to use this stored raw data to recomputed the position of the PT and any related curve information. This is how you keep an alignment dynamic, allowing you to recompute the alignment as you edit it.

Curve Data Combinations

There are many combinations of curve data that you can enter right in the Traverse View to compute a curve. Although the radius and arc length are common, you can lots of combinations. Here are a few.

Recalling the Outgoing Tangent

Create a new traverse point immediately after the curve.

You will see the outgoing tangent direction displayed.

Specifying a Point of Intersection Point Type

Highlight the point label field of the point that you want to be a PI.

When you highlight a point that has been designated as a PI and select the horizontal curve dialog box, TPC looks for a PC and PT on either side of the PI. If it does not find a PC and PT, it inserts them automatically when curve data is entered. The inserted points will have the same point label as the PI, but with the extensions PC and PT.

In all other respects, PI's are treated like occupied points. This is a great way to float in PC's and PT's.

Entering a Curve at a PI

TPC will insert a PC point before the PI and a PT point after the PI if they do not already exist. Both the inserted PC and PT points will be positioned on the tangents, equal distance from the PI. The Traverse View now displays the inverse between the PC and PT (as if the PI was a side shot from the PC). The PC and PT are treated like occupied points from then on.

Using the Horizontal Curves Dialog

As you enter data in the Horizontal Curve dialog, you will notice that the field names change state to indicate which data you have entered. These states indicate which data is given and which data is computed. When you enter a number, the field name becomes depressed to show that data is being held. If a value is computed, its field name is released. To change the state, just click on the field name.

From this dialog, you can create dozens of curves by combining the data you are given. Once you understand the basic operation of the Horizontal Curves dialog box, you can make it work with almost any combination of data you run across.

Saving the Computed PI and PR

TPC will check for existing point labels, ask you to change the labels if necessary and save the points.

When the PI and PR are saved, they become part of the survey even though they may not be used in any traverse. To include them in any of the traverses, recall them by their point labels.

Grid vs Ground / Geodetic

The curve distances and directions displayed in the Traverse View and the COGO dialogs are based on the distance type of each alignment traverse. For example, if an alignment traverse is formatted for ground distance at project elevation, radii, arc and tangent lengths will be ground distance at project elevation.

This gives you the option of working with alignment parameters at ground (use a ground distance type) or grid (use grid distance type).

See Geodetic Alignments.


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Related Topics

Entering Spirals
Creating Stations at Intervals
Computing a Predetermined Area
Computing New Coordinates for a Point
Creating a Point at a Distance and Offset
Creating Points at Intersections
Creating Multiple Points on a Line or Grade
Computing Offset Intervals for Posting Line
Creating Offsets to a Straight Line
Inversing Between any Two Points
Creating R-O-W Offsets
Creating Corner Offsets
Creating Offsets to an Alignment
Creating Station/Offset
Horizontal Curve Fitting
Labeling COGO Points
Plotting COGO Points