Measurement: Length measured with `Std_Measure` is attached to geometric center, not midpoint

Problem description

The Length mode of Std_Measure attaches the annotation to the geometric center (or barycenter) of the curve, not to its midpoint. It means that when measuring the length of a non-straight curve, the annotation is not attached to the curve.

Workbench affected?

Core (App, Gui,...)

Steps to reproduce

Use Std_Measure on a curved edge or Draft wb spline

Expected behavior

The annotation is attached to the curve midpoint.

Actual behavior

The annotation is attached to the geometric center.

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