Line Geometry Data

Description

Design Lines and Setting Out Objects comprise a series of segments whose 'Link Type' may be 'Line', 'Arc' or 'Transition'. The segments are connected with each segment start position and angle matching the end position and angle of the previous segment, so there are no sharp changes in direction.

Line

A straight line between two defined points. It is stored as start-point and end-point coordinates.

Arc

A circular arc. It may be defined in a variety of ways, but is stored as start-point, mid-point and end-point coordinates.

Transition

Either a clothoid or a cubic spline.

Clothoid

A curve whose curvature changes linearly with distance along it (sometimes called a spiral). Points on the clothoid are defined using Fresnel Integrals. It is stored as a series of points at uniform spacing along the curve.
Cubic Spline

A curve that fits through all of a series of user-defined points. It is a 'Natural Spline' (i.e. the second order derivatives of the curve at the end points are zero). This means that the slope at the ends is controlled only by the points on the line. So, when a cubic spline is used, it must always be the first segment to be defined. It is stored as the coordinates of the points (defined by the user) through which it passes.

Format

Line geometries may be copied to and pasted from the windows clipboard as text, separated by spaces or tabs, with the following format on each line:

X Y T

where X and Y are the coordinates and T is the Link Type.

Note: data can be copied from the detailed Data Report for Design Lines or Setting Out Objects as the data is in this same format.

Example

X        Y       Type         « Header String

21.0093  0.1860  T 

21.5216  0.2000  T

22.0338  0.2146  T

22.5461  0.2299  T

23.0583  0.2460  T

23.5704  0.2627  T

24.0826  0.2802  L

47.0686  1.0829  A

58.5654  1.3393  A

70.0651  1.3057  A

This example contains the data from a table of four rows whose link types are, in order, 'Transition', 'Line', 'Arc' and 'None'. The 'transition' data in the above example contains the coordinates of the points that lie on the transition curve (21.0093, 0.1860) to (24.0826, 0.2802). The 'line' data is the start-point (24.0826, 0.2802) and end-point (47.0686, 1.0829). The 'arc' data is the start-point (47.0686, 1.0829), mid-point (58.5654, 1.3393) and end-point (70.0651, 1.3057).

The transition curve in the above example is for a clothoid, in which data is stored as coordinates at equal centres. For a cubic spline the stored coordinates, transferred to clipboard, are the (relatively fewer) coordinates with which the user has defined the curve.

The first line of the data can contain a header string, which is disregarded when importing provided it comprises text characters only.