Last updated July 28, 2026
BL draws building lines on a skewed grid. You pick two points along the direction the building runs, the snap grid rotates to match, ortho comes on, and from then on your lines go square to the building instead of square to the screen.
It is by Lawrence Lieberman of Hogan, Schoch & Associates in Sebastopol, California — the same author as BANK — version 1.0, dated 9 February 1991.
The idea is worth more than the routine
Anyone who has drawn a building set at 23 degrees to north knows the problem. Ortho is the fastest way to draw, and on a skewed building ortho is useless, so you turn it off and fight every line with object snaps and typed angles.
The fix is to rotate the snap grid rather than the drawing. Ortho follows the snap angle, not the world axes, so once the grid is aligned to the building, ortho is square to the building too. Everything that felt slow goes back to being fast, and the geometry is still stored at its true angle — nothing has been rotated, only the way you are working over the top of it.
That is the whole trick, and it survives the routine. Even if you never load this file, the technique is worth having.
Command reference
- BL — asks whether to re-use the current snap angle or set a new one, then starts a polyline.
- ZERO — sets the snap angle back to 0 degrees.
Two commands, not one. The listing below describes only BL; ZERO exists and is announced by a prompt, which is easy to miss and worth knowing before you find yourself with a permanently crooked crosshair.
Both names are short and generic. BL especially is the sort of two-letter name people assign to their own aliases, so check it is free before you load this alongside a personal toolset.
What the code actually does
The alignment is done by handing two picked points to the SNAP command’s Rotate option, which sets both the snap origin and the snap angle in one move. Ortho is then forced on, and you are told to type ZERO when you want the grid straight again.
Two things in the file are worth knowing before you rely on it, and neither is obvious from running it once.
Ortho is saved and never restored
The first line of BL reads the current ortho setting into a variable. Nothing ever reads it back. The intent is plain enough — put the drawing back the way it was — but the restoring half was never written, so BL leaves ortho on when it finishes, and so does ZERO.
That variable is also not in the routine’s list of locals, so it is left behind in the drawing session rather than cleaned up. Harmless in itself, but it is the fingerprint of an unfinished intention rather than a decision.
The re-use path has no points to re-use
Answer Y at the prompt and you pick a base point and an alignment point, the grid rotates, and the polyline starts at your base point and runs to your alignment point. That path works.
Answer anything else and the two points are nil. They are declared local to BL and only ever assigned inside the routine that does the picking, so on the re-use path nothing has set them. The polyline still starts — but not where the code means it to, and you will be picking the start point yourself.
The snap angle does survive between runs, because it is a system variable and stays where the last run put it. So the re-use path does the useful part. It is only the automatic start point that is missing.
If the snap rotation line fails
The SNAP command’s option list has changed over the years, and the Rotate option is the part most likely to have moved out from under this file. Test that step first — pick your two points and see whether the crosshairs actually turn.
If they do not, the same job is two system variables, which will not go anywhere:
(setvar "snapbase" p1)
(setvar "snapang" (angle p1 p2))SNAPBASE moves the grid origin to your first point; SNAPANG rotates it. The angle function returns radians and SNAPANG expects radians, so no conversion is needed. Drop those two lines in where the SNAP call is and the routine does the same thing by a route that has not changed since 1991.
The modern alternative is a rotated UCS, which does the same for ortho and also brings text, hatch and dimensions along with it. For a quick run of building lines the snap angle is less to undo.
How to load it
Unzip BL1.zip and load it with APPLOAD. Note that the file inside is named BL.LSP, not BL1.LSP — the download name and the file name differ, which matters if you are searching your support folder for it later. No support files. Our AutoLISP guide covers loading.
Step-by-step usage
- Type BL.
- Answer Y to set a new angle. Any other key re-uses the angle already set.
- Pick a base point on the building line, then a second point along it. The crosshairs turn to match.
- Keep picking points. Ortho is on and now runs with the building.
- Type ZERO when you want the grid square to the world again.
- Turn ortho off yourself if you want it off. The routine will not.
The two points in step 3 do not have to be on the building line itself. Any two points along the right direction will do — a grid line, a boundary, the edge of a survey feature.
Compatibility notes
February 1991, so written-for rather than tested-on. It is thirty lines of plain AutoLISP with no dialog boxes and no Express Tools calls, so nothing here requires the full product; LT users on LT 2024 or later, the release that brought AutoLISP to LT, should be able to run it. See what runs on AutoCAD LT.
It draws a polyline and changes three system variables. Nothing is deleted or modified, so the worst case is an unwanted polyline and a crooked snap grid — one undo and one ZERO.
Download
| Name: | BL |
| Description: | Used to create building lines, etc. Works in polyline mode. Allows re-use or reset of snapangle, and forces orthomode. |
| Type: | AutoCAD AutoLISP Routine |
| Author: | Lawrence Lieberman |
| File Size: | 1 Kb |
| Cost: | Free |
| Worked on: | AutoCAD |
| Download File: | BL1.zip |
Related routines
- BANK — by the same author, from the same office.
- Draw Architectural Walls — the walls that go on the building lines.
- WALLS — another take on the same job.