Array 4-Point Adaptive Family
on TWO Curves

Select the Source Mass or Adaptive Component

The leftmost dropdown (comboBox1) lists every Adaptive Component (FamilyInstance), Wall, and Floor placed in the project. Selecting an item triggers UpdateCurveCache() which walks the element's full geometry tree — unpacking GeometryInstance objects recursively — and extracts all Solid edges via edge.AsCurve(). Curves are sorted longest first then both Curve 1 and Curve 2 dropdowns are populated from the same shared list.

Select Curve 1 — the Primary Rail

comboBox2 (red border) lists all extracted edges labelled Curve N (Length: X.XXX m, FamilyInstance) — or Edge N for mass geometry. Select the edge that will carry the P1–P2 side of each instance.

Selecting Curve 1 auto-fills the End field in the Curve 01 parameter panel: End = curve.Length × 0.3048 − 0.001 (m). The selected curve is highlighted red in the 3D canvas. A Reset button appears in the canvas area.

Select Curve 2 — the Secondary Rail

comboBox4 (yellow border) is populated with the same curve list. Select the edge that will carry the P3–P4 side of each instance — this is typically the opposite edge of the deck form (e.g., the far fascia of the cross-section).

Selecting Curve 2 auto-fills the End2 field in the Curve 02 parameter panel. The selected curve is highlighted yellow in the canvas. Both highlighted curves are now visible simultaneously for visual confirmation.

Optionally Reverse Either Curve

The two ⇄ buttons — checkBoxReverse1 (after comboBox2) and checkBoxReverse2 (after comboBox4) — are styled checkboxes that reverse their respective curve via curve.CreateReversed(). The canvas and station dots update immediately.

Pick the 4-Point Family

The family picker (comboBox3) sits in the left 55% of Row 2, inside a GroupBox labelled "Select Family". Select the adaptive family whose four points will be set to the computed station positions. The list is sorted alphabetically and deduplicated by family name.

Runtime 4-Point Re-Validation at RUN

Even though the dropdown pre-filters, RUN performs a second check before placing anything. The steps are identical to the pre-filter: open a temporary transaction → create a test instance → count GetInstancePlacementPointElementRefIds() → roll back. If the count ≠ 4, placement is blocked with a clear error message and the model remains unchanged.

Set Curve 1 — Start, End, Interval Space, Gap

Start (default: 0) — station along Curve 1 where the first instance begins. End — auto-filled from curve length, can be reduced to restrict the array range. Interval Space (default: 2 m) — arc length each instance spans (distance between P1 and P2). Gap (default: 0.2 m) — empty space between consecutive instances.

After each instance, the algorithm advances by Space + Gap on Curve 1. The station componentSize = Space − Gap must be positive (enforced with an error if not).

Invalid entries turn the text box background light pink and block RUN until corrected. Valid entries restore the white background. The canvas station dots refresh on every keystroke.

Set Curve 2 Parameters (Control Both mode only)

When "Control Both Curves" is active, the Curve 02 GroupBox enables. It exposes the same four fields — Start2, End2, Interval Space2, Gap2 — but they independently control how stations are computed on Curve 2. Curve 2 can have different spacing, start offset, or sub-range from Curve 1.

The algorithm matches each Curve 1 station to the nearest Curve 2 station using FindCorrespondingStation(). If the suggested station is within ½×Space2 of the projected intersection, it snaps to the projected point. Otherwise it uses the regular incremental value.

Visual Layers in the Canvas

• Fine grid — grey lines at 10 m spacing on the XY ground plane
• Coarse grid — slightly darker lines at 50 m spacing
• All form edges — white, all extracted curves before selection
• Curve 1 — highlighted red, 3 px — the edge selected in comboBox2
• Curve 2 — highlighted yellow, 3 px — the edge selected in comboBox4
• Station dots — yellow, 4 px radius — one dot per station on Curve 1 and Curve 2
• XYZ axis indicator — pinned bottom-right (X=red, Y=green, Z=blue)

Canvas Interaction — Alternating Curve Selection

Clicking on an edge in the canvas uses a selectingFirstCurve toggle flag. The first click sets Curve 1 (comboBox2), the second click sets Curve 2 (comboBox4), and the flag resets. This means clicks alternate — first selection, second selection, first selection, etc.

Pre-Run Checklist — What RUN Validates

Before opening any Revit transaction, RUN checks all of these in order — failing any one stops execution immediately with a clear error:

1. Both curves selected — cachedSelectedCurvePoints1 and cachedSelectedCurvePoints2 must both be non-null and non-empty. Error: "Please select two curves from the form edges."
2. Family selected — comboBox3.SelectedItem must not be null. Error: "Please select an adaptive family with 4 points."
3. Family found in document — searches by exact name match. Error if not found.
4. Family symbol exists — retrieves the first FamilySymbol from the Family's symbol IDs.
5. 4-point re-validation — rolls back a temporary transaction. If adaptive point count ≠ 4: "The family must be an adaptive component with exactly 4 adaptive points."
6. Valid station ranges — Start/End/Space/Gap are parsed and checked for logical validity. Invalid values show specific error dialogs.

Review the Alignment Info Bar and Click RUN

The Alignment info GroupBox at the bottom confirms the active mass element name and both selected curves. Verify this before clicking RUN.

Placement — One Transaction, Four Points Per Instance

Inside the transaction "Place Multiple Adaptive Components", for each station range the code retrieves 4 XYZ positions from the pre-computed list — indices i×4, i×4+1, i×4+2, i×4+3 — and assigns them:

• rp1.Position = point1 → P1 — Curve 1 span start
• rp2.Position = point2 → P2 — Curve 1 span end
• rp3.Position = point3 → P3 — Curve 2 corresponding start
• rp4.Position = point4 → P4 — Curve 2 corresponding end

A progress bar tracks execution from 0→30% (station computation) → 30→80% (instance placement loop) → 100% (commit). If a single instance fails due to geometry, it is silently skipped via continue and placement resumes with the next span.