CROSSHAIR draws a crossed pair of centrelines through an arc, circle or ellipse, at a length and rotation you drag out. It is a small routine and it does one thing, which is most of the point.
What CrossHair does
DIMCENTER will centre-mark a circle, but the size comes from DIMCEN and the marks are always orthogonal to the current UCS. When you want the centrelines to run at the angle of the thing they belong to — a bolt hole on a sloping flange, a pipe on a skewed run — you are back to drawing them by hand.
This lets you drag both the length and the rotation, and see the result before committing.
How to use it
- Load the routine with
APPLOAD, or put it on your support file search path. - Type
CROSSHAIR. - Pick the arc, circle or ellipse to mark.
- Drag to set the length and rotation of the centrelines, and click.
How it works
The centre point is taken from the picked object rather than from where you clicked, so the marks are genuinely centred regardless of how carefully you picked. The two lines are drawn through that point at the dragged rotation and its perpendicular.
Because the length is dragged rather than taken from a system variable, the marks can be made to overhang the object by whatever looks right at the scale you are working — which is the usual reason for drawing them by hand in the first place.
Notes and limits
- Arcs, circles and ellipses only. These are the objects with a defined centre to mark.
- Centrelines should be chain lines. Set the current layer or linetype before running it — the routine draws the geometry, it does not choose your drafting standard.
- The result is two ordinary lines, so they can be trimmed, extended and edited normally.
- One undo group covers both lines.
Download and details
| Name | CrossHair — centre-mark a curved object with draggable centrelines |
| Download | CrossHair.lsp — 3.5 KB, plain AutoLISP source. Downloads directly; no zip to unpack. |
| Type | AutoCAD AutoLISP routine |
| Command | CROSSHAIR |
| Requires | nothing beyond a CAD platform with AutoLISP. |
| Source size | 3.5 KB, 98 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
- Pen sizes and line types — the chain line convention centrelines should use
- Dimensioning to metric standards — where centre marks fit in the conventions
- More free AutoLISP routines on this site
- Wisey’s Steel Shapes — free structural steel section drawing program