How to find the intersection between a line and a plane in AutoCAD?

It's not something we do every day, but when you need it, how do you do it?

Well, you can achieve this by positioning the UCS so that the ZX plane corresponds to the desired plane, then switching to front view and finally using the projected intersection. You can also use TRIM/EXTEND. But it's a bit tedious and not very elegant.

Another solution is to use the online calculator (command CAL):

1. Start the POINT command;
2. Type 'CAL. Note the apostrophe before CAL, it's to tell AutoCAD that you want to launch the command transparently. Some commands can be launched this way, which allows you to not cancel the currently running command;
3. Type ilp(cur,cur,cur,cur,cur). ilp is a function that calculates the intersection between a line and a plane (Intersection Line-Plane). The 5 cur that follow are used to tell AutoCAD that you want to select points with the mouse. The first two points must be on the line, the last three on the plane.

There you go, you now have the intersection between a line and a plane in AutoCAD!

The CAL command can do many other things, such as calculating distances, angles, manipulating vectors, etc.

I regularly use it to calculate distances for the OFFSET command:

Command: OFFSET

Current settings: Erase source=No  Layer=Source  OFFSETGAPTYPE=0
Specify offset distance or [Through/Erase/Layer] <Through>: 'cal
>>>> Expression: 15.5/2

Resuming OFFSET command.

Specify offset distance or [Through/Erase/Layer] <Through>: 7.75

When the calculation is done with integers, like 15/2, you don't need CAL, but it doesn't work as soon as you have real numbers.

Another example: calculating the center of gravity of a triangle:

Command: POINT

Current point modes:  PDMODE=0  PDSIZE=0.0000
Specify a point: 'cal
>>>> Expression: (cur+cur+cur)/3
>>>> Enter a point:
>>>> Enter a point:
>>>> Enter a point:

Resuming POINT command.
Specify a point: 2023.6727542407,1678.1318497134,0

You can consult the CAL command documentation to learn more about other available functions: https://help.autodesk.com/view/ACD/2026/ENU/?guid=GUID-B29F2EF7-12C8-423C-91F5-3852E6AF1514

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