ELEVMID-bgol (Midpoint Elevation Interpolation)

Command Type: AutoLISP routine (works in AutoCAD, BricsCAD, ZWCAD and most AutoLISP-compatible CAD platforms)
Developed by: BGol Community, bgol.in

Inspired by the general concept of midpoint elevation interpolation used in survey and profile drafting. This is an original, independently written routine, new file name, new command name, new source code, created so the CAD community has a free, editable, open-source alternative.

Overview

ELVM covers the single most common interpolation need in survey drafting: given two known elevation texts, compute and place one new elevation label at their exact midpoint, both geometrically and numerically. The command keeps running so you can process several text pairs in one session.

How to Use

1. Load ELEVMID-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type ELVM at the command line and press Enter.
3. Select the first elevation TEXT entity.
4. Select the second elevation TEXT entity.
5. A new TEXT entity is created at the geometric midpoint of the two insertion points, showing the averaged elevation value, on layer BGOL-ELVM.
6. The command automatically prompts for another pair, keep selecting pairs, or press Escape to finish.

Why Use It

• Covers the most common case, "I need one value halfway between these two" without needing the more general multi-point or distance-based routines.
• Fast, minimal input, just select two texts and the midpoint result is created automatically at the correct position and value.
• Reduces manual error, removes manual averaging and manual text placement, both frequent minor sources of drafting inconsistency.

Where to Use It

• Adding a single intermediate spot elevation between two known survey points when only one extra value is needed.
• Quick QA/estimation tasks where a rough halfway elevation is useful without running a full multi-point interpolation.
• Any land-survey drawing task requiring fast, simple midpoint elevation estimates.

Notes

• The command loops automatically so multiple text pairs can be processed in a single run; press Escape to exit.
• Text height for the new label matches the first selected text's height (falls back to 2.5 if unavailable).
• Values are formatted to 2 decimal places, matching common survey precision conventions.
• Source code is fully open, feel free to study, modify, and redistribute it under the same open, free-for-all spirit.

Credits

Developed and shared for the CAD community by BGol Community. Website: https://bgol.in/ Free and open-source, use it, modify it, share it, for personal or commercial work alike.