What makes it different.
Once your photo is corrected and scaled, Smart Trace does the tracing. It is LensCAD's own tracing technology, developed and tuned against hand-measured parts. It works out what the shapes in the photo are and draws each line, arc and corner where the edge actually is, so what comes back is measured geometry rather than a sketch over the picture.
On our benchmark parts, traced outlines come back at roughly 0.1 mm median error against hand-measured ground truth. How accuracy is measured →
Measured, named, and yours to steer.
- One-tap tracing. Press Run and Smart Trace draws the whole part: outer profile, holes and interior features, each on the real edge in the photo. Most parts come back ready to export.
- Named parts, real layers. Smart Trace names what it traces (body, trigger, nozzle) and each named component lands on its own DXF layer, in its own colour, exactly how your CAD software expects it. A layer in LensCAD is the component name, so renaming one renames it in CAD.
- Five styles per run. One run returns five interpretations: Smooth, Organic, Auto, Polygonal, and Edge outline, an outline taken directly from the edges in the photo. Switch between them instantly, or mix: the outline from one style and the interior from another. Switching is always free; you pay for the run.
- You aim it. Brush over just the part you care about, or type a plain-English prompt such as "trace only the circular holes". Two quality levels: Normal for most parts, High for the stubborn ones.
- Each view knows the others. On a multi-view part every run remembers which side it traced, and later runs are told what the earlier ones measured. If a view comes back the wrong size for the side you labelled it, LensCAD says so and offers to relabel it, before a mislabelled view builds the wrong 3D model.
- Cancel freely. Stop a run mid-flight and the run comes back. A run that dies underneath you restarts itself once, billed as a single run, and a failure tells you what went wrong and whether trying again would help.
- Clean up in one press. Thin out crowded points without changing the shape, then weld the seams where two components share a real edge so they butt together exactly. Anything genuinely redundant is dropped; anything that carries its own outline is kept.
- The manual tools have not gone anywhere. They are how you take a trace the last mile: nudge a corner, standardize hole sizes, add dimensions. Or skip the AI entirely and hand-trace when you prefer to. The CAD editor →
The finer points.
The five stylesWhat each interpretation is for
- Smooth is the cleanest, fewest-point reading of the part. On some parts that is exactly what you want; it is the least precise of the five.
- Organic keeps curves as curves and never straightens a side or squares a corner. For cast, moulded and hand-shaped parts.
- Auto keeps straight sides straight, rounds the corners that are rounded into true fillets, and leaves genuine curves alone. The default for most machined and fabricated parts.
- Polygonal gives straight sides and sharp corners only, with no fillets. A trapezoid comes back as a handful of vertices, not a curve.
- Edge outline is an outline taken straight from the edges in the photo. On a part lying on the reference sheet it is often the most accurate of all, and its row tells you what fraction of the part it found.
Several styles can be shown at once, each in its own tint, and shapes from different styles land on separate layers so mixing them is a matter of erasing what you do not want.
Runs and re-runsWhat a run costs, and when it costs nothing
Every Smart Trace run costs real compute, so runs are counted. Re-running the same view uses half a run, and a run that fails or that you cancel is given back automatically. New accounts start with 3 free runs; Pro includes 30 a year and Studio 100, added monthly, and a top-up on a paid plan adds 20 runs for $15. Full pricing →
The guide brush and promptsScoping a run to the part you mean
Paint the guide brush over the region you want traced and Smart Trace works inside the paint, ignoring the clutter around it. The brush picks its own colour so it stays visible on wood, tan and orange parts, and a stroke that overhangs the part or misses a corner of it does no harm. On a thin part such as a wire hook, painting it is what gets the wire itself traced rather than the space it encloses.
A prompt steers the run in plain English: which components matter, what to skip, what a shape is. Pressing Run puts the brush away and keeps the painted mask.
Runs that go wrongRetries, and what a failure says
A shape-dense photo comes back slightly simpler rather than not at all. A run that dies mid-flight retries itself once, billed as one run. A failure stays on screen where you were watching, says what failed, and says whether trying again would help or whether painting a guide region is the better answer. Every export carries a plain-text report of how each run went.