Add area and total length/perimeter CAD dock floater values (Request in QGIS)

[qgis-bot]

Request for documentation

From pull request qgis/QGIS#64496
Author: @nyalldawson
QGIS version: 4.0

Add area and total length/perimeter CAD dock floater values

PR Description:

(temporarily includes qgis/QGIS#64481)

Adds (optional) area and total length/perimeter floater values

Unlike the other floater values which have a boolean hidden/visible state only, these floater values support display in either
ellipsoidal or cartesian measurements.

It's tricky to decide if the default should be ellipsoidal or cartesian measurements. Elsewhere we tend to use ellipsoidal measurements by default, but the whole CAD tools are built strictly around Cartesian measurements (eg distance constraints are always Cartesian). If we default to Ellipsoidal measurements here to match the rest of QGIS measurement tools, then users will get confused if they use a distance constraint for a set distance and then immediately see a DIFFERENT total length measurement readout! On the other hand, if we default to Cartesian measurements to match the CAD constraints, then users will get confused when the CAD floater shows a total area, and then immediately after digitizing the identify tool show will show a DIFFERENT total area!

So to make things as user friendly as possible, we:

1. FORCE the user to make the choice. The area and length measurements default to hidden, and to show them the user must select the floater menu, "Show Area" submenu -> and then pick between "hidden", "show cartesian area" or "show ellipsoidal area" (and similar for total length). There can be NO ambiguity as the user has explicitly made a choice between them!
2. We show a small icon next to the floater area/total distance labels, with a curved line if the measurement is ellipsoid based, or a straight line if it's cartesian based

Screencast_20260109_100801.webm

Fixes #50789

Funded by QGIS Danish User Group

Commits tagged with [need-docs] or [FEATURE]