OVDIFF-bgol (Find Difference in Overlapping Text)

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 overlapping-text difference utilities used in earthwork/survey CAD 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

OVDF detects pairs of numeric TEXT entities that sit at (or very near) the same insertion point, for example, an "initial level" and a "final level" stacked on top of each other on different layers in an earthwork drawing, and creates a new text at that location showing the signed numeric difference between the pair, in a distinguishing color.

How to Use

1. Load OVDIFF-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type OVDF at the command line and press Enter.
3. Select the numeric TEXT entities to scan for overlaps, then press Enter to confirm.
4. The routine groups entities by matching insertion point (within a small coincidence tolerance) and computes the signed difference (second value − first value) for every overlapping pair found.
5. A new difference text is created next to each pair on layer BGOL-OVDF, colored green for a positive difference and red for a negative difference, so cut/fill sense is visible at a glance.

Why Use It

• Automates Earthwork Comparison, removes the need to manually cross-reference and subtract two overlapping elevation values at every grid point across a large earthwork drawing.
• Enables Difference Contouring, the resulting difference values at each grid point can be used as input for generating a difference/cut-fill contour map of the site.
• Visual Distinction, colour-coding the calculated difference by sign makes it immediately identifiable apart from the original overlapping source values.

Where to Use It

• Earthwork projects, comparing initial (existing ground) and final (design/finished) levels at each grid point to quantify cut or fill depth.
• Preparing input data for a difference-contour visualization of how elevations have changed across a site.
• Any survey task involving two overlapping numeric text values at the same location that need their difference computed and displayed in-place.

Notes

• Overlap detection uses a small coincidence tolerance (*bgol-ovdf-tol*, default 0.01 drawing units) rather than requiring an exact point match; edit the constant near the top of the .lsp file if your drawing's overlapping pairs sit slightly further apart.
• Only the first matching pair found for each text is used, a text already paired is not paired again with a third overlapping text.
• 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.