Civil 3D sample lines: how to create them automatically, at any station, and stop redoing them after every change

A sample line tells Civil 3D where to cut the road and how wide. At each line, Civil 3D cuts the sources you choose (existing ground, the corridor, its surfaces, even pipe networks) and builds the cross section from them.

Everything that follows depends on them:

• Section views, one per line.
• Cut and fill volumes, computed between sections.
• The mass haul diagram and section sheets.

That's why sample lines live in a sample line group, which belongs to an alignment. The group stores the sources, styles and labels for all its lines.

The command is on the Home tab › Profile & Section Views panel › Sample Lines. At the command line it's CREATESAMPLELINES.

Pick the alignment. For the first group, the Create Sample Line Group dialog opens, where you choose sources and styles. Then the Sample Line Tools toolbar appears, with five ways to create them:

The swath width on each side is set when you create them: a fixed width, or snapped to another alignment, such as a right-of-way line, so the width changes along the road. If it falls short, the section is clipped and the volume is incomplete.

When someone asks whether sample lines can be generated automatically, the first answer is that Civil 3D already does it, more than most people use.

By range of stations opens a dialog with what a plan set needs:

• The range: from the start to the end of the alignment, or between two stations.
• Different increments on tangents, curves and spirals. The Wisconsin DOT Civil 3D knowledge base, for example, uses 50 ft on tangents, 25 ft on curves and 50 ft on spirals, with 75 ft swaths on each side.
• Where increments count from: Absolute Station, from station 0+00, or Station Range Start. With Absolute Station, lines land on round stations such as 0+50 and 1+00, even if the range starts at 0+13.
• Additional sample controls: at the range start and end, at horizontal geometry points (the start and end of curves and spirals) and at superelevation critical stations.
• The swath width on each side: fixed, or snapped to an offset alignment.

From corridor stations creates one line at every corridor station. It's the most faithful option, because each section shows exactly what the corridor computed. It's only available if the alignment already has a corridor.

And the lines follow the alignment. Each sample line has a Lock To Station option, in its properties on the Sample Line Data tab:

• Checked: if the alignment changes, the line slides to the new location of its station.
• Cleared: the line stays where it is and Civil 3D recalculates its station.

Edit a line. Select it to see its grips: one slides it along the alignment, others stretch each side and others change its angle.

Change every width at once. On the Sample Line Tools toolbar, Edit Swath Widths for Group extends or trims every line in the group to the same width.

Add sample lines to an existing group. Run Sample Lines again, pick the same alignment and choose the existing group on the toolbar. New section views don't join the existing section view group on their own: use Move to Section View Group, because the Update command doesn't re-sort them. Sheets aren't regenerated automatically either.

Delete sample lines. Select them in the drawing and erase them. Their section views go with them.

Rename and renumber. Civil 3D assigns each line's number in station order. The name comes from a template with a counter, such as SL-1 or SL-2. To show the station on the plans, use the sample line label. Civil 3D has no command to rename every line in a group at once.

All of the above works well on one alignment with regular increments. Real projects are where the problems start:

• Stations from a list. The ones on the plans, culverts, section changes, or the ones a reviewer asks for. Civil 3D doesn't read a list: you create them one at a time with At a station.
• Many alignments. A subdivision with 30 streets means 30 groups and the same dialog 30 times, with the risk of missing a source or a width.
• Design changes. The lines follow the alignment, but they aren't added or removed on their own. If the alignment gets longer, the new stretch has no lines. If a new curve appears, its geometry points have no line. If the corridor frequency changes, the lines stay at the old stations.
• Redoing them is costly. The usual fix is to delete and recreate. But deleting the lines deletes their section views, and the sheets must be built again.
• Swath width. It's fixed or runs to an offset alignment. If a high fill spreads past it, the section is clipped, and sometimes nobody notices until the volumes are checked.
• Names. If the plans identify each section by its station, renaming the lines is manual work.

With Dynamo, no coding. Dynamo is Civil 3D's visual programming: you connect blocks instead of writing code. Since Civil 3D 2025.1 it includes out-of-the-box nodes to create sample line groups and sample lines, plus one to create section views. On earlier releases, the free Camber package also has sample line nodes. A typical script reads stations from Excel and creates a line at each one: we cover it in 10 Dynamo scripts for Civil 3D.

With a C# plugin. The Civil 3D API has what's needed: SampleLineGroup.Create creates the group on an alignment and SampleLine.Create creates each line at a station, or from points you define.

// One group per alignment and one sample line at each station in the list
ObjectId group = SampleLineGroup.Create("Plan set sections", alignmentId);

foreach (double station in stations)          // read from the project's Excel file
{
    string name = station.ToString("0+00");   // 150 -> "1+50"
    SampleLine.Create(name, group, station);
}

That's two calls. What takes the work, and what makes the plugin useful, is everything around them: reading and validating the list, computing each line's width, assigning sources and styles, deciding which lines to add or remove after a change, and logging what it did.

The full comparison is in Dynamo or C# for Civil 3D and Revit. If your team wants to learn the API, start with Civil 3D API in C#, getting started.

We build custom Civil 3D plugins. For sample lines, a typical plugin:

• Reads your rules: increments on tangents, curves and spirals, plus an Excel list of stations with culverts, section changes and the points reviewers ask for.
• Works on every alignment in the drawing in one pass, with one group per alignment.
• Computes each line's width so it covers the corridor and its slopes, plus a margin.
• Names each line after its station and assigns the sources, styles and labels from your template.
• After a change, compares the lines that exist with the ones that should: it adds the missing ones, removes the extra ones and leaves the rest untouched, section views included.
• Logs what it did in a report, so you can check it before building the sheets.

If you also need the section views or the sheets, they go into the same plugin. We cover that in automated plan production in Civil 3D and Revit.

How we work:

1. Diagnosis (1 week, free): we look at the task on one of your projects and write down the rules.
2. Prototype (1 to 2 weeks): we validate the logic on your project.
3. Development (2 to 4 weeks): the C# plugin, tested on your own models.
4. Installation: an installer for the whole firm, a button on the Civil 3D top toolbar, a manual and documentation.
5. Support: updates with every new Civil 3D release.

The source code belongs to your company: the plugin is yours.