> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/cadd/caddfromsection-cadd.md). # CADD From Section **CADD From Section** generates a 2D drawing automatically by cutting through your 3D bridge model along an alignment. It is how you produce the cross-sections, elevations, and deck plans on your drawing sheets without redrawing them by hand. Every time the bridge geometry changes — span lengths, pier locations, deck thickness, bearing offsets — the section drawing rebuilds from the latest model. You decide: * **Where the cut goes** (a station along the alignment for a cross section, an offset from centerline for a profile, an elevation for a plan). * **Which view** (cross section perpendicular to alignment, longitudinal profile parallel to alignment, or top-down plan). * **What's shown and how it's drawn** (which objects appear, which don't, which line weights and colors, how each line is offset for theoretical-position dimensions). Everything else — finding the right intersection of every face with the cut plane, sorting cut from projection from hidden, following horizontal curves and superelevation — happens automatically. ## Choosing the alignment **Alignment:** The bridge alignment that drives the cut. The section's position is expressed *relative to* this alignment — by station, by offset from centerline, or by elevation — so when the alignment changes (bridge geometry revised, station equation added, profile updated), every section view that references it updates with the new geometry. If the project has multiple alignments (e.g., centerline, ramp, ground), pick the one the section is naturally referenced against — usually the bridge centerline for cross sections and elevations, the ramp/centerline for ramp sections. If you change which alignment a section uses, the cut location is interpreted in the new alignment's stationing, not converted from the old one. ## What kind of view The **Clip Mode** parameter selects between three cuts. Each is appropriate for different drawing types. ### Cross — for cross-section drawings A vertical plane perpendicular to the alignment at one station. Use this for: * Pier elevation / pier section drawings (one section per pier) * Bent and bent-cap details * Deck cross sections at any reference station * Skewed pier cuts (combine with Skew Angle below) The view's horizontal axis runs left-to-right along the bridge cross direction; the vertical axis runs up. Looking at the drawing, you're standing up-station looking down-station (toward higher stations), unless **Flipped** is on. **Station:** Distance along the alignment where the cut is taken. A station of zero is the alignment's start. **Skew Angle:** Additional rotation of the cut plane about vertical, in degrees. Use to draw skewed pier cuts on bridges where piers cross the alignment at an angle (for example, a 30° skew on a pier crossing a curved alignment). ### Profile — for elevation drawings A vertical cut parallel to the alignment, offset to one side by a perpendicular distance, running the full length of the alignment. **Profile Sub-Mode** picks how the cut treats a curved alignment: * **Developed** — The cut follows the alignment's horizontal curve (the same surface the 3D clip slider shows) and the result is unrolled onto a flat sheet, so even on a curved bridge the elevation reads straight: stations along the bottom, elevations along the side. This is the developed elevation of bridge plan sets. Horizontal distances are measured along the section's alignment, so lengths on an offset line are not to scale — note it on the sheet the way plan sets do ("Developed elevation along centerline of bridge"). Edges are projected by their endpoints, so a straight 3D chord far off the alignment is drawn straight on the sheet too — a curved line is only as smooth as the model's meshing. Switching a saved Flat section to Developed moves the sheet origin (X becomes the station), so annotations placed on it will sit elsewhere relative to the linework. Sections created from the 3D **+ CAD** button use this sub-mode. * **Flat** — A single vertical plane tangent to the alignment at mid-station. Identical to Developed on a straight alignment; on a curved one it cuts a chord, so only use it when you specifically want a true planar section. Sections saved before the sub-mode existed are Flat. Use this mode for: * Bridge elevation sheets (the headline drawing) * Girder profile views with bearings, joints, and pier locations marked * Long-span profile sheets where you want to see the full alignment in one view **Offset:** Perpendicular distance from the alignment to the cut. Positive offset is to the right of the alignment when looking up-station; negative is to the left. Offset zero cuts on centerline. Offset to one side for a girder line; offset further for a parapet or fascia line. ### Plan — for plan-view drawings A horizontal cut producing a top-down view. **Plan Sub-Mode** picks between three flavors: * **Flat** — A single horizontal cut at one elevation across the whole project. Use this for foundation plans, footing layouts, and any plan where you want a true horizontal slice at one elevation. Set **Elevation** to the cut elevation. * **Vertical Profile** — The cut follows the alignment's profile grade — the cut elevation rises and falls with the bridge. Use this for top-of-deck plans and any plan that should track the bridge grade rather than sit at a fixed elevation. Set **Profile Offset** to the vertical distance above (positive) or below (negative) the alignment's centerline elevation. For a top-of-deck plan, this is roughly half the deck thickness. * **Profile w Cross Slope** — Same as Vertical Profile, but the cut also tilts to follow the cross slope (superelevation): the surface is the alignment's vertical profile plus the cross-slope elevation at each point's station and offset. Use this for top-of-deck plans where superelevation matters — bearing seat layouts, drainage details, anything where the deck surface isn't flat in cross section. The 3D slider previews the same surface; to keep a deck top that lies on the cut from flickering, the preview draws faces within a few inches of the cut as themselves, while the section is exact. **Elevation** — The cut elevation (Flat sub-mode only). **Profile Offset** — Vertical offset from the alignment surface (Vertical Profile and Profile w Cross Slope sub-modes). Positive is up. **Flipped:** Reverses the view normal. Use when the cut puts you on the opposite side of the structure from where you want to see it. ## Projection depth A section drawing usually shows two kinds of lines: the **cut** (what the plane sliced through) and the **projection** (what's behind, drawn as silhouette). Projection depth controls how much of "behind" gets drawn. **Near Depth:** Distance in front of the cut plane (toward the viewer) within which projection edges are still drawn. Default zero — clips strictly at the cut plane. Increase if you want to see geometry that sits in front of the cut, useful for stepped sections. **Far Depth:** Distance behind the cut plane (away from the viewer) within which projection edges are drawn. Set to a small value for a clean section with no clutter behind the cut, or to the full pier width / span length to see the complete silhouette. For a clean pier elevation sheet, set Far Depth to the pier's full thickness so the back face of the pier shows as a projection line behind the section line — without including the next pier's projection. **Hidden Line Removal:** On for sections created from the 3D **+ CAD** button; a section saved before it existed, or added from the CAD tree, has it off until you turn it on, so its drawing, dimensions and bindings stay as they were. Projection edges that sit behind nearer geometry — the four girders behind the fascia girder, cross-frames behind the web, the far face of a pier cap — are taken out of the projection and kept as **Hidden** lines (dashed), which are off for every object type until you turn them on in the Objects panel. While it is on, **centerlines are off by default** as well (a pile axis through a visible pile is the same clutter); tick **CL** on a type to show them. Occlusion is sampled along each edge (a few inches apart, budgeted per drawing), so a member narrower than the step in front of a very long line can be missed. This is what makes a full-width elevation readable: set Offset just outside the fascia, Far Depth to the full bridge width, and the sheet shows the deck edge, the fascia girder, and the piers, one line each. Switch it off to get every silhouette in the slab regardless of what covers it, as earlier versions drew. A hidden run that coincides with a visible line is not drawn twice. In DXF and DGN export, hidden lines land on their own `-HIDDEN` layer/level so the seed or template can give them a dashed style. **Tolerance:** Distance band within which a face is treated as exactly on the cut plane. Default `0.001` (in your project's length units) is right for most projects. Increase to `0.005` or `0.01` if a coplanar face — typically a deck top, top of footing, or top of pier cap — isn't being picked up as a cut line. ## Showing and hiding objects Section drawings often show too much. Bridge sections especially: girder cross-frames, miscellaneous metal, drainage hardware, future reservations. The Objects panel lets you remove these without modifying the model. **Hide an object:** uncheck the box next to its name in the Objects panel. The object's cut, projection, and centerlines all disappear. Right-click for "Hide all of this type" (e.g. hide every cross-frame at once), "Show only this object" (isolate), or "Show all" to reset. **Hide a category for a type:** the per-row checkboxes (Cut / Proj / Hidden / CL) let you keep an object but suppress one of its line classes. Common uses: turn off projection for parapets in a pier section so they don't clutter the view; turn off centerlines for bearings in an elevation drawing; turn **Hidden** on for piles so they show dashed below the footing (Hidden is off by default for every type). **Outline:** keeps only the type's outer boundary (its envelope) and drops interior lines. The Cut / Proj / Hidden boxes still choose which of those boundary lines are drawn, so a covered object's envelope shows dashed only where Hidden is on. **Show a type through what covers it:** tick **Show through** on the type. Its lines are drawn solid wherever they are, as if nothing were in front — the framing-plan case: girders and cross-frames through the deck in a plan view, while the deck edge and everything else keep hidden-line removal. The type still hides what is behind it. Use **Hidden** instead when the convention calls for dashed lines. **Hide a single edge:** in the Edges panel, the eye icon next to a chain hides only that edge. Use for visually distracting edges that aren't structurally meaningful (back-of-fillet duplicates, etc.). ## Edge offsets — drawing to theoretical positions Bridge details often dimension to theoretical positions rather than to as-modeled geometry. A bearing seat top is dimensioned to its theoretical seat elevation (not to the modeled-thickness top), a pier face is dimensioned to its theoretical face (not to the as-modeled formliner inset). The **Edge Offsets** dialog lets you push individual edges parallel to themselves by a specified distance. Click "Edges" on an object's row, pick the chain (top, bottom, left, right — labels are auto-generated based on each chain's orientation), and type a distance. Positive offsets push the edge outward (away from the object centroid), negative inward. Corners adjust automatically so the offset rectangle stays a rectangle. This is for drawing presentation only — the underlying 3D model is unchanged. ## Levels and line styling By default the section uses four line categories: * **Cut** — heavy black, solid. The "section line" — bold so it dominates. * **Projection** — medium gray, solid. Visible silhouette behind the cut. * **Hidden** — light gray, dashed. Hidden silhouette (off by default). * **Centerline** — red, center-line dash. Beam centerlines, axis symbols. You can route any object type's edges to a CAD level instead, so the level's color, weight, and dash style apply. This is the right way to set conventions like "all cut concrete on a Concrete level" or "all girder lines on a Steel level" — assign once in the Level Mappings and any new girder added to the model picks up the correct styling automatically. ## Showing the alignment on the drawing The alignment(s) that the cut intersects can be drawn as centerlines on top of the section, with station ticks. Per-alignment settings in the Alignment Display dialog: * **Visible** — Show or hide the alignment line. * **Show Stations** — Whether to label every interval-th station with text. * **Color** — Hex color for the alignment line and ticks. * **Station Interval** — Distance between station ticks (50 for elevation drawings, 10 for detail sections). * **Tick Size** — Tick mark length on screen. For a typical pier section, hide the alignment display (no centerline overlays the structure). For an elevation drawing, show the alignment with station ticks every 50 ft (or 10 m) and station labels on. ## Common workflows ### Pier section sheet 1. Drop a CADD From Section into a CAD document. 2. Set **Alignment** to the project centerline. 3. Set **Clip Mode** to **Cross** and **Station** to the pier's station. 4. If the pier is skewed to the alignment, set **Skew Angle** to match. 5. In the Objects panel, hide deck-only items (parapets, barrier rails, lighting standards) so the pier dominates. 6. Map cut concrete to a "Concrete" level so cut-line styling matches your sheet conventions. ### Bridge elevation 1. CADD From Section → **Clip Mode = Profile**, **Offset = 0** (alignment centerline). 2. **Far Depth** = the half-width of the widest pier so the full pier silhouette projects. 3. **Near Depth** = 0 so geometry in front of the cut is clipped. 4. In Per-Type Visibility, turn off Projection for the parapets (they crowd the elevation). 5. In Alignment Display, show the alignment with station ticks every 50 ft. 6. Add station offsets and elevation dimensions on top of the section. ### Top-of-deck plan with superelevation 1. CADD From Section → **Clip Mode = Plan**, **Plan Sub-Mode = Profile w Cross Slope**. 2. Set **Profile Offset** = +half the deck thickness so the cut sits at top of deck. 3. In Per-Type Visibility, turn off Projection per type (you only want what's at the deck surface). 4. Map bearing edges to a "Bearings" level so they show with bearing-line conventions. 5. Add station-offset annotations at the bearing centerlines. ### Foundation plan 1. CADD From Section → **Clip Mode = Plan**, **Plan Sub-Mode = Flat**. 2. Set **Elevation** to your foundation working elevation (top of footing). 3. Hide everything except substructure objects in the Objects panel. 4. Add ordinate dimensions for footing corners. ## Troubleshooting **Nothing draws.** The cut plane is missing the model. For Cross mode, check Station against the alignment range. For Profile, check Offset against the model's transverse extent. For Plan / Flat, check Elevation against the model's vertical extent. If only projection is missing, Far Depth is at the default zero — increase it. **A flat surface (e.g. deck top, top of footing) isn't being picked up as a cut line.** Raise Tolerance from `0.001` to `0.005` or `0.01` and refresh. The face is just outside the band the cut considers "on plane." **Hidden objects come back after a model rebuild.** They were renamed by the rebuild — re-hide under the new name. Hidden state is keyed to object name. **Section is correct but mirrored.** Toggle **Flipped**. The default view direction may be putting you behind the structure. **Profile section has angular polylines where you expect smooth curves.** The alignment's resolution is too coarse. Refine the alignment. **Sections don't update after a model change.** They should — open and close the CAD document, or use Refresh. If they still don't update, the objects in the cut were deleted and re-added with new names; re-open the section's Objects panel to verify. **Edge offsets don't stick after editing geometry upstream.** Edge identification is based on the object's edge order, which can change if the underlying 3D mesh is regenerated. Re-pick the edge in the Edge Offsets dialog and the offset reapplies. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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