ISOPROJECT takes a flat orthographic view you have already drawn — a front elevation, a plan, a side — and projects it into the left, right or top isoplane of an isometric drawing.
What IsoProject does
AutoCAD has isometric snap, which helps you draw in isometric. It has nothing that converts an existing view into one. That is the gap this fills: draw the view square, where it is easy to get right and easy to check, then project it.
How to use it
- Load the routine with
APPLOAD, or put it on your support file search path. - Draw the view square, and get it right.
- Type
ISOPROJECT. - Select the objects and pick the reference point everything measures from.
- Choose left, right or top isoplane.
How it works
Isometric drafting is a shear plus a horizontal squash, measured from one reference point. Take any point’s offset from that reference as u across and v up. Writing 0.866 for cos 30°:
Left plane x = 0.866u y = v - 0.5u
Right plane x = 0.866u y = v + 0.5u
Top plane x = 0.866(u - v) y = 0.5(u + v)
In the left and right planes, vertical stays vertical and unscaled while horizontal tips to 30° below or above. In the top plane both axes tip, one to 30° and the other to 150°.
This is isometric drawing, not true isometric projection. Lengths along the isometric axes stay true rather than being scaled by 0.8165. That is what drafting practice uses, because it lets you measure a length straight off the drawing.
Circles become ellipses, which is the only correct answer. A circle seen in an isoplane is an ellipse; a sheared circle is not. Arcs are replaced by a fitted polyline through points sampled every five degrees, because a sheared arc is an elliptical arc and AutoCAD has no direct way to build one from a shear.
Notes and limits
- Straight-segment polylines are handled in place, vertex by vertex — no exploding first.
- Polylines carrying bulges are refused and reported. A bulge is a circular arc, and shearing one gives an ellipse a bulge cannot describe.
- Text is moved and re-set in an obliqued style so it lies in the plane.
- One undo group covers the projection.
Download and details
| Name | IsoProject — project orthographic geometry into an isometric plane |
| Download | IsoProject.lsp — 14.0 KB, plain AutoLISP source. Downloads directly; no zip to unpack. |
| Type | AutoCAD AutoLISP routine |
| Command | ISOPROJECT |
| Requires | nothing beyond a CAD platform with AutoLISP. |
| Source size | 14.0 KB, 343 lines |
| Error handling | Yes — a *error* handler restores every system variable it changed, on cancel as well as on error. |
| Undo | The whole operation is wrapped in a single undo group, so one U reverses all of it. |
| Compatibility | AutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer. |
| Author | YZ, August 2026 |
| Licence | Free to use, supplied “as is” with no warranty. |
References
- Axonometric: drawing in 3D — the conventions behind isometric drawing
- CIRCLETOELLIPSE LISP — converting circles to ellipses directly
- More free AutoLISP routines on this site
- Wisey’s Steel Shapes — free structural steel section drawing program