Orthographic drawings

Use a drawing to inspect a part's outline, see hidden features, or exchange a 2D view with another application. Smith computes line visibility from the native BREP. The result keeps curves, independently of the triangles in a 3D preview.

Choose a view

Create the part and evaluate it once. Drawings from the result reuse that geometry.

alias Smith.{Drawing, Plane, Sketch}

plate = Sketch.rounded_rectangle(50, 30, 3)
  |> Smith.extrude(8)
  |> Smith.counterbore(on: Plane.xy(z: 8), at: {-15, 0},
    diameter: 4, bore_diameter: 8, bore_depth: 3, through: :all)
{:ok, part} = Smith.evaluate(plate)
{:ok, top} = Drawing.new(part, on: :xy)
{:ok, front} = Drawing.new(part, on: :xz)

The normal points toward the viewer; the viewing direction is its negative. Plane-local X points right and plane-local Y points up.

A custom plane defines an oblique orthographic view. Moving its origin in the plane changes the drawing's coordinate origin. Moving it along the normal does not change the image size or coordinates. There is no perspective scaling.

view = Plane.new(normal: {1, -1, 1}, x_direction: {1, 1, 0})
{:ok, oblique} = Drawing.new(part, on: view)
{:ok, shifted} = Drawing.new(part, on: Plane.xy(origin: {10, 5, 100}))

Sharp boundaries and silhouettes are included. tangents: true additionally includes smooth G1 boundaries between faces, which can help explain fillets. Surface seams and isoparametric lines are omitted.

Inspect and sample

drawing.visible and drawing.hidden are native edge collections in view-local XY at Z=0. They support OCEx queries and BREP serialization. The drawing records the input's source_revision; treat its fields as read-only.

{:ok, visible_edges} = OCEx.edges(top.visible)
true = visible_edges != []
{:ok, lines} = Drawing.polylines(front, tolerance: 0.01, angular_tolerance: 0.1)
true = lines.hidden != []

Each returned polyline represents one edge. Closed edges repeat their endpoint. Edges are not joined into loops, and coincident projections are not merged. An edge viewed exactly end-on has no line extent and is omitted. Empty layers are normal, particularly for a single face or sphere silhouette.

Display in Livebook

SVG previews need no server-side graphics process. Install Kino alongside Smith, then leave the image as the cell's last value:

{:ok, svg} = Drawing.svg(top, hidden: false, title: "Plate · Top")
Kino.Image.new(svg, :svg)

This is a static 2D drawing. Smith.Kino.render(part) provides the rotatable 3D view. Use both when inspecting a model. The drawing notebook builds a counterbored plate and compares top, front, and oblique views.

Write SVG and DXF

Both formats use millimeters. Curves are sampled with the same defaults as Drawing.polylines/2: 0.03 mm linear deflection and 0.1 rad angular deflection. Choose a smaller linear tolerance for finer curves. These are OCCT sampling parameters, not a certified global deviation bound for arbitrary splines.

directory = Path.join("output/drawings", part.revision)
File.mkdir_p!(directory)
{:ok, svg_path} = Drawing.write(top, Path.join(directory, "top.svg"),
  hidden: false, tolerance: 0.01, padding: 5, stroke_width: 0.25)
{:ok, dxf_path} = Drawing.write(front, Path.join(directory, "front.dxf"),
  tolerance: 0.01)

write/3 infers the format from the extension. It requires an existing parent directory and overwrites an existing file only after serialization succeeds. Using the source revision in the directory keeps views of different revisions apart. Drawing.svg/2 and Drawing.dxf/2 return binaries when you manage storage.

SVG sets physical width and height in mm. Its viewBox includes the selected geometry, padding, and half the stroke width at each edge. The vertical reflection adapts CAD's upward Y to SVG's downward Y. Hidden lines are gray and dashed; visible lines are black and painted above them. hidden: false omits hidden geometry. An empty drawing returns :empty_drawing.

DXF uses AC1015 (AutoCAD 2000), $INSUNITS=4, and LWPOLYLINE entities. It retains the drawing's XY coordinates and has VISIBLE and HIDDEN layers with continuous and dashed linetypes. Arcs, circles, and splines are exported as polylines. Empty drawings are allowed. There are no dimensions, text, blocks, or paper layouts.

Assemblies and limits

Passing an assembly draws installed manufactured parts. References and printable extras are excluded. Pass an evaluated Assembly.view(result, :exploded) to draw that pose, or use Assembly.fetch/2 to draw one member or reference. Visibility is computed across the selected geometry, so one part can hide another.

These are view drawings, not dimensioned engineering sheets or cutting-tool paths. Validate scale and contours in the receiving application before using a file for manufacture. The SVG/DXF writers do not import drawings or infer sketches from them. Use Smith.export/3 for verified printable STL/3MF bundles.