FreeCAD/FreeCAD

Measurement: `Std_MassProperties` can’t use edge to calculate inertia about it

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#28921 opened on Mar 31, 2026

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Good first issueMod: MeasurementType: Feature

Description

Problem description

Std_MassProperties can compute inertia around a LCS axis or datum line. It is not possible to select an edge on a solid or surface, unless by creating a datum line attached to it before starting the feature.

Workbench affected?

Core (App, Gui,...)

Steps to reproduce

Start Std_MassProperties, select a solid, select custom reference, click Select…, then click a straight edge of the solid.

Expected behavior

The reference field is filled with the selected edge identifier and the inertia is computed about it.

Actual behavior

The content of the list of objects to measure changes, the inertia doesn’t change.

Development version About Info (in Safe Mode)

OS: Ubuntu 24.04.3 LTS (KDE/plasma/xcb)
Architecture: x86_64
Version: 1.2.0dev.20260324 (Git shallow) AppImage
Build date: 2026/03/24 17:14:33
Build type: Release
Branch: (HEAD detached at 1bc5980a7)
Hash: 1bc5980a7ff302a55c617181e774cd5cd2a9443a
Python 3.11.14, Qt 6.8.3, Coin 4.0.8, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, IfcOpenShell 0.8.2, OCC 7.8.1
Locale: French/France (fr_FR)
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Light/
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Drag at cursor
Logical DPI/Physical DPI/Pixel Ratio: 96/117.596/1
Installed mods:
  * Cables Workbench 0.3.5
  * Fasteners Workbench 0.5.44
  * Curves workbench 0.6.71
  * Curved Shapes 1.0.14
  * SheetMetal Workbench 0.8.10
  * FusedFilamentDesign 0.26.100
  * FreeCAD-DFM-Workbench-main

Last known good version (optional)

Not applicable

Contributor guide

Tech stack
cpppython
Domain
desktop
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++QtFreeCAD API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Investigate how Std MassProperties handles reference selection in the GUI. Look at the selection filter and how edges are distinguished from datum lines. The fix likely involves modifying the selection logic in the command handler (e.g., src/Mod/Part/App or src/Gui) to accept edges for inertia calculation. Examine the existing code for how datum lines are processed and extend it to handle edge geometries.