C3d Sample Lines

Civil 3D Sample Lines and Section Views

Use this skill when working with sample line groups, sample lines, section views, or when labeling gravity/pressure pipe networks in cross-section views.

Object Hierarchy

Alignment
  └── SampleLineGroup (via GetSampleLineGroupIds())
        └── SampleLine (via GetSampleLineIds())
              ├── .Station — chainage at which this sample line cuts
              ├── GetSectionIds()   → Section objects (one per sampled source)
              └── GetSectionViewIds() → SectionView objects (one per view at this station)

Accessing Sample Line Groups

CivilDocument civilDoc = CivilApplication.ActiveDocument;
ObjectIdCollection alignmentIds = civilDoc.GetAlignmentIds();

foreach (ObjectId alignId in alignmentIds)
{
    Alignment alignment = tr.GetObject(alignId, OpenMode.ForRead) as Alignment;
    ObjectIdCollection slgIds = alignment.GetSampleLineGroupIds();

    foreach (ObjectId slgId in slgIds)
    {
        SampleLineGroup slg = tr.GetObject(slgId, OpenMode.ForRead) as SampleLineGroup;
        ed.WriteMessage("Group: {0}\n", slg.Name);

        ObjectIdCollection sampleLineIds = slg.GetSampleLineIds();
        ed.WriteMessage("  Sample lines: {0}\n", sampleLineIds.Count);
    }
}

Iterating Sample Lines

SampleLineGroup slg = tr.GetObject(slgId, OpenMode.ForRead) as SampleLineGroup;

foreach (ObjectId slId in slg.GetSampleLineIds())
{
    SampleLine sl = tr.GetObject(slId, OpenMode.ForRead) as SampleLine;

    double station = sl.Station; // chainage value along the alignment

    ObjectIdCollection sectionIds     = sl.GetSectionIds();     // Section objects
    ObjectIdCollection sectionViewIds = sl.GetSectionViewIds(); // SectionView objects
}

Section Types — Gravity vs. Pressure

Each SampleLine holds one Section per sampled source (surface, gravity network, pressure network, etc.). Cast to the appropriate subtype:

foreach (ObjectId sectionId in sampleLine.GetSectionIds())
{
    Section section = tr.GetObject(sectionId, OpenMode.ForRead) as Section;

    if (section is SectionPipeNetwork gravitySection)
    {
        // Gravity pipe network section
        ObjectId networkId = gravitySection.SourceId; // links to Network
    }
    else if (section is SectionPressurePipeNetwork pressureSection)
    {
        // Pressure pipe network section
        ObjectId networkId = pressureSection.SourceId; // links to PressurePipeNetwork
    }
    // Other types: SectionSurface, etc.
}

SourceId is the key link from a Section back to the model object (network, surface, etc.) that was sampled.

Finding the Section Network ID for Label Creation

Before creating labels in a section view, you must find the Section object (SectionPipeNetwork or SectionPressurePipeNetwork) that corresponds to your chosen network. This ID is required by all section label Create() methods as the sectionNetworkId parameter:

// Gravity
ObjectId sectionPipeNetworkId = ObjectId.Null;
foreach (ObjectId sectionId in sampleLine.GetSectionIds())
{
    Section section = tr.GetObject(sectionId, OpenMode.ForRead) as Section;
    if (section is SectionPipeNetwork sn && sn.SourceId == targetNetworkId)
    {
        sectionPipeNetworkId = sectionId; // this is the sectionNetworkId for labels
        break;
    }
}

// Pressure
ObjectId sectionPressureNetworkId = ObjectId.Null;
foreach (ObjectId sectionId in sampleLine.GetSectionIds())
{
    Section section = tr.GetObject(sectionId, OpenMode.ForRead) as Section;
    if (section is SectionPressurePipeNetwork spn && spn.SourceId == pressureNetworkId)
    {
        sectionPressureNetworkId = sectionId;
        break;
    }
}

If sectionNetworkId is ObjectId.Null, the network is not sampled at this sample line — skip it.

Creating Section Labels

Once you have a sectionViewId and sectionNetworkId, create labels for individual parts:

// ── Gravity section labels ────────────────────────────────────────────────
// PipeSectionLabel.Create(sectionViewId, pipeId, sectionNetworkId, partIndex, styleId)
ObjectId pipeLabelId = PipeSectionLabel.Create(
    sectionViewId, pipeId, sectionPipeNetworkId, 0, pipeStyleId);

// StructureSectionLabel.Create(sectionViewId, structureId, sectionNetworkId, partIndex, styleId)
ObjectId structLabelId = StructureSectionLabel.Create(
    sectionViewId, structureId, sectionPipeNetworkId, 0, structureStyleId);

// ── Pressure section labels ───────────────────────────────────────────────
// All three share the same long signature
ObjectId pressurePipeLabelId = PressurePipeSectionLabel.Create(
    sectionViewId, pipeId, sectionPressureNetworkId,
    0 /* partIndex */, 0.5 /* ratio */, new Vector3d(1, 0, 0),
    labelStyleId, (DimensionAnchorOptionType)0, 0.0);

ObjectId fittingLabelId = PressureFittingSectionLabel.Create(
    sectionViewId, fittingId, sectionPressureNetworkId,
    0, 0.5, new Vector3d(1, 0, 0),
    labelStyleId, (DimensionAnchorOptionType)0, 0.0);

ObjectId appurtLabelId = PressureAppurtenanceSectionLabel.Create(
    sectionViewId, appurtId, sectionPressureNetworkId,
    0, 0.5, new Vector3d(1, 0, 0),
    labelStyleId, (DimensionAnchorOptionType)0, 0.0);

Note: If the part is not present in the section view, Create() throws ArgumentException — wrap in try/catch and treat as "not in this section".

Detecting Existing Section Labels

Check before creating to avoid duplicates:

// Gravity — takes sectionViewId only
ObjectIdCollection existingPipeLabels      = PipeSectionLabel.GetAvailableLabelIds(sectionViewId);
ObjectIdCollection existingStructureLabels = StructureSectionLabel.GetAvailableLabelIds(sectionViewId);

// Inspect each label's FeatureId to know which part it covers
foreach (ObjectId labelId in existingPipeLabels)
{
    PipeSectionLabel label = tr.GetObject(labelId, OpenMode.ForRead) as PipeSectionLabel;
    ObjectId featureId = label.FeatureId; // the pipe ObjectId
}

// Pressure — takes sectionViewId + partId + sectionNetworkId
// Returns label ids if part is in section; throws if part is not in section
ObjectIdCollection existingPressurePipe = PressurePipeSectionLabel.GetAvailableLabelIds(
    sectionViewId, pipeId, sectionPressureNetworkId);

Label Style Selection for Section Views

var labelStylesRoot = civilDoc.Styles.LabelStyles;

// Gravity pipe cross-section styles
var crossSectionStyles = labelStylesRoot.PipeLabelStyles.CrossSectionLabelStyles;
foreach (ObjectId styleId in crossSectionStyles) { /* pipe section styles */ }

// Gravity structure styles (same collection for all views)
var structStyles = labelStylesRoot.StructureLabelStyles.LabelStyles;

// Pressure pipe cross-section styles
var pressCrossSection = labelStylesRoot.GetPressurePipeLabelStyles().CrossingSectionLabelStyles;

// Pressure fitting and appurtenance styles (same collection for all views)
var fitStyles = labelStylesRoot.GetPressureFittingLabelStyles().LabelStyles;
var appStyles = labelStylesRoot.GetPressureAppurtenanceLabelStyles().LabelStyles;

Discovering Which Networks Are Sampled in a Sample Line Group

Use this pattern to populate a "select network" list by scanning all sections:

var sampledNetworkIds = new HashSet<ObjectId>();

foreach (ObjectId slId in slg.GetSampleLineIds())
{
    SampleLine sl = tr.GetObject(slId, OpenMode.ForRead) as SampleLine;
    if (sl == null) continue;

    foreach (ObjectId sectionId in sl.GetSectionIds())
    {
        Section section = tr.GetObject(sectionId, OpenMode.ForRead) as Section;

        // Gravity
        if (section is SectionPipeNetwork sn)
            sampledNetworkIds.Add(sn.SourceId);

        // Pressure
        if (section is SectionPressurePipeNetwork spn)
            sampledNetworkIds.Add(spn.SourceId);
    }
}

Then open each discovered ObjectId as Network (gravity) or PressurePipeNetwork (pressure).

Gotchas

• SampleLine.GetSectionIds() returns one Section per sampled source — a section view may have multiple sections (surface, gravity network, pressure network, etc.)
• SectionPipeNetwork.SourceId links to the Network, not to the SampleLine or SectionView
• PipeSectionLabel.Create() throws ArgumentException (not returns Null) when a pipe has no crossing at that section view — always try/catch
• PressurePipeSectionLabel.GetAvailableLabelIds() also throws when the part is absent from the section — use the same try/catch pattern for detection
• Section label partIndex is 0-based; passing 0 works for single-crossing scenarios
• sectionNetworkId in label Create() is the SectionPipeNetwork/SectionPressurePipeNetwork ObjectId — NOT the model network ObjectId

Related Skills

• c3d-root-objects - Accessing alignments through CivilDocument
• c3d-pipe-networks - Gravity and pressure pipe network part IDs used in section labels
• c3d-label-styles - Label style navigation for cross-section styles
• c3d-alignments - Alignment and profile view concepts