Section Line Indicators#

from pathlib import Path
from dessia_drawing.core import Drawing
from drawing_tools.config.default_language_configs import DEFAULT_ENGLISH_CONFIG, DEFAULT_FRENCH_CONFIG
from drawing_tools.featured_drawing import FeaturedDrawing

_DATA_DIR = Path("data/json")
drawing = Drawing.from_json(str(_DATA_DIR / "condor/condor_BEAM_ASSY.json"))
featured_drawing = FeaturedDrawing(drawing, language_configs=[DEFAULT_FRENCH_CONFIG, DEFAULT_ENGLISH_CONFIG])
featured_sheet = featured_drawing.sheets[3]
featured_view = featured_sheet.views[3]

featured_view.plot_data_section_lines().plot()
featured_sheet.plot_data_section_lines().plot()

Section line indicators are symbols on technical drawings that show where a section cut or auxiliary view is taken. Drawing Tools detects them automatically and provides structured access to their properties.

See also

For a complete working example demonstrating section line detection, see the script scripts/section_lines_and_auxiliary_view_indicators.py in the repository.

What is a Section Line Indicator?#

A section line indicator consists of:

  • Two collinear arrows pointing in the same direction, marking the cut line

  • A letter identifier on each arrow (e.g., “A”, “B”, “K”)

  • Optionally, a cross-reference to a sheet number (e.g., “4/5” meaning sheet 4 of 5)

      A            A
      |            |
------+------------+------
      v   4/5      v

These symbols indicate where section views (e.g., COUPE A-A), detail views, or auxiliary views are cut from. The identifier letter corresponds to the view title on the target view (e.g., a section line “A” produces the view “COUPE A-A”).

Accessing Section Line Indicators#

Section line indicators are detected automatically on each FeaturedView:

for sheet in featured_drawing.sheets:
    for view in sheet.views:
        for indicator in view.section_line_indicators:
            info = indicator.identifier_info
            print(f"{info.identifier} cross_ref={info.cross_reference} "
                  f"detection_source={indicator.detection_source}")

SectionLineIndicator Properties#

Each SectionLineIndicator provides:

  • ``identifier_info`` — an IdentifierInfo object containing:

    • identifier: full identifier string (e.g., "A", "B2")

    • letter: letter part (e.g., "A", "B")

    • number: numeric suffix or None (e.g., 2 in "B2")

    • cross_reference: sheet cross-reference string (e.g., "4/5") or None

    • cross_reference_left: sheet number (e.g., 4) or None

    • cross_reference_right: total sheets (e.g., 5) or None

  • ``arrow_locations`` — list of two Point2D positions (the two arrow tips)

  • ``arrow_direction`` — Vector2D shared direction of both arrows

  • ``detection_source`` — how the indicator was detected:

    • "symbols" — from a single TypeNote annotation with FillArrow leaders

    • "symbols (standalone xref)" — same, but cross-reference was a separate text

    • "composites" — from CompositeEntity arrows paired with standalone TypeNote labels

  • ``source_entities`` — the original dessia_drawing entities

View-Level Visualization#

The following visualization shows section line indicators detected on the “DETAIL 2” view of the BEAM ASSY drawing (Sheet 3). Each indicator is highlighted with a colored bounding rectangle and labels showing its identifier, cross-reference, detection source, and arrow direction.

Source: condor_BEAM_ASSY.json, Sheet 3, DETAIL 2

featured_view = featured_drawing.sheets[3].views[3]  # DETAIL 2

featured_view.plot_data_section_lines().plot()

Sheet-Level Visualization#

Section line indicators can also be visualized at the sheet level, showing all indicators across all views on a single sheet:

Source: condor_BEAM_ASSY.json, Sheet 3

featured_sheet = featured_drawing.sheets[3]

featured_sheet.plot_data_section_lines().plot()

Each indicator is assigned a different color from a rotating palette to distinguish overlapping indicators.

Detection Sources#

Section line indicators can be encoded in two different ways in CAD files. Drawing Tools handles both representations transparently:

Symbols (detection_source="symbols"): A single TypeNote annotation carries both the arrows (as FillArrow leaders) and the text labels. This is the most common representation.

Composites (detection_source="composites"): Each arrow is a separate CompositeEntity and the letter labels are standalone TypeNote annotations positioned nearby. The detector matches labels to arrows by spatial proximity, then groups arrow pairs by identifier and collinear direction.

Both sources are merged in the section_line_indicators property. You can check indicator.detection_source to know which representation was used.

Counting Indicators#

# Number of section line indicators in a view
count = featured_view.section_line_indicator_count

# Iterate and filter
indicators_with_xref = [
    ind for ind in featured_view.section_line_indicators
    if ind.identifier_info.cross_reference is not None
]