Design polylines relative to a reference path

Pythagoras can automatically calculate the vertical design of one or more polylines based on a reference path, either by a fixed slope (grade) or by a fixed height offset (elevation difference).

This workflow is especially useful in road and infrastructure projects, where edges, ditches, and curb lines need to follow the road axis consistently. By defining the slope or elevation offset once, Pythagoras ensures that all design polylines remain vertically aligned with the reference path.

Before you start you will need

• Reference object (Path):
  This is the 'line' with valid height (Z) information. It will serve as your vertical reference.

• Target polyline(s):
  These are the basic polylines you want to adjust. They can be parallel to the path, but don’t have to be.

• Optional: Point(s) on the target polyline

WORKFLOW

1. Create a Path on your reference line

The path acts as the vertical reference.

• Go to Create Path.

• Click the first point of the reference line-object.

• Double-click a segment to generate a path along the entire line object.

2. Select the reference and target polylines

• Select the Path (with Z).

• Shift+select one or more target polylines.

• Go to Calculation > Design > Polyline relative to Path
  or right-click → Edit > Design Polyline relative to Path.

The dialog Polyline relative to Path opens.

3. Choose how elevations are calculated

A. Fixed Gradient (Slope / Grade)

Keeps the target polyline at a constant slope from the path.

• Enter the slope (e.g. –2% to create a ditch falling away from the road).

The target polyline will be calculated vertex by vertex along the full alignment.

B. Fixed Height Difference (Elevation Offset)

Keeps the target polyline at a fixed vertical offset from the path.

Two ways to define it:

Point Nr (requires a point on the target polyline)

• Select the point number from the dropdown.

• The tool compares the Z of the point and the Z of the path at that XY location.

• It then applies this difference to the full target polyline.
  

Delta Z (no point required)

• Enter a chosen vertical difference (e.g. –0.20 m for a curb edge 20 cm lower than the road axis).

4. Confirm and check

• Click OK.

• Review results in 2D and 3D.

Pythagoras calculates the elevation of every vertex on the target polyline relative to the path, using the slope or height offset rule you selected.

This saves you from manual height editing and keeps your design polylines consistent with the reference.

VIDEO

The following video shows how this works: