# Horizontal Curve Fitting

TPC can find the best fit curve through a series of survey points. You may be able to tie an as-built center line that passes through tangents and curves, then let TPC help you find the best fit lines.

## Selected Points

In TPC, you fit a horizontal curve to a series of survey points. These points can be consecutive points in a traverse, selected points in the Points Manager, selected points in a drawing or all the points in a traverse.

## Types of Fitted Curves

TPC can compute three types of fitted horizontal curves to a series of points.

### Least Squares

Uses least squares to compute the best fit curve.

This is a minimally constrained solution, so the end point of the curve can vary as needed to create the best fit. Once the curve is computed, TPC computes the end points of the curve so that they are as close a possible to the first and last selected points.

TPC uses the first and last selected points to compute the positions of the end points of the best fit curve. So if point 200 is the first selected point and point 210 is the last, TPC will compute end points for the curve that are as close to points 200 and 210 as possible. These will therefore be prependicular offsets to the end points of the best fit curve.

### Average

The option assumes that the First point is a PC and the Last point is a PT. TPC then computes the radius of each point as if it were a POC. The average of these radii is displayed as the Radius.

TPC does not compute new end points of the best fit curve with this option. Instead, it assumes you want to retain the existing PC and PT and fit the points between them.

## Typical Sequence

You will often fit a line as follows.

• Select the points you want to fit a line to in the Points Manager, Traverse Manager, a Traverse View or the Drawing View.
• Choose COGO | Fit Horizontal Curve to display the Fit Horizontal Curve Dialog.
• Select the Option you want and choose Compute.
• (Least Squares Option) Choose the point labels you want for the computed points and choose Save and Plot to see the computed end points.

If you selected points via a traverse (entire traverse or selected traverse points), you can update the traverse to include curves between all the points used in the computation.

• Choose Apply Radius to the traverse points.
• Choose Undo to undo the Apply Radius command.

## Selecting Points

You can select points using the following methods.

### From the Traverse View

• Select the points you want to include in the best fit curve. If you will be including all the points in the traverse, select just one point in the traverse.
• Choose COGO | Fit Horizontal Curve to display the Fit Horizontal Curve Dialog.

### From the Drawing View

TPC will set the What list to Entire Traverse: [traverse name] using the traverses that drew the object you right clicked.

### From the Points Manager

• Select the points you want to include in the best fit curve. Remember that the first and last points selected determine the computed end points of the best fit curve.
• Right click any selected point and choose COGO | Fit Horizontal Curve to display the Fit Horizontal Curve Dialog.

### From the Traverses Manager

• Select the traverse with the points you want to include in the best fit curve. The entire traverse will be used for the computation.
• Right click the selected traverse and choose COGO | Fit Horizontal Curve to display the Fit Horizontal Curve Dialog.

TPC will set the What list to Entire Traverse: [traverse name] using the traverse you selected.