[Layout] Geospatial PDF has incorrect georeference info for the overlapping region of the Map items

[agiudiceandrea]

What is the bug or the crash?

A Geospatial PDF (ISO 32000 Extension), exported from a print layout containing 2 (or more) totally or partially overlapping Map items, has incorrect georeferencing information for the overlapping region of the Map items.

The zip archive testlayout.zip contains a vector layer (CRS EPSG:32633 "WGS 84 / UTM zone 33N") with 2 line features (each one having a Cartesian length of 1 km) and a simple project testlayout.qgz with a print layout in which there are 2 partially overlapping Map items (both CRS EPSG:32633) representing the same layer.

The Geospatial PDF Layout 1.pdf has been exported setting the Geospatial PDF (ISO 32000 Extension) option.

Opening the exported Geospatial PDF with Adobe Acrobat Reader 2024.005.20320 on Windows 10 is it possible to verify that, while the lines length in non overlapping regions is correctly measured (1 km), the line length in the overlapping region is incorrect (0,67 km)

Video_2025-01-23_223900.mp4

Note: this is a simpler version, with a simpler reproducible example, of the issue report #60204.

Steps to reproduce the issue

1. open the provided QGIS project
2. create a Geospatial PDF (ISO 32000 Extension) with default settings
3. open the Geospatial PDF with Adobe Acrobat Reader
4. measure the line features using the measuring tool

Versions

QGIS version	3.40.2-Bratislava
QGIS code revision	14826ca1
Libraries
Qt version	5.15.13
Python version	3.12.8
GDAL/OGR version	3.9.3
PROJ version	9.5.0
EPSG Registry database version	v11.016 (2024-08-31)
GEOS version	3.13.0-CAPI-1.19.0
SQLite version	3.46.1
PDAL version	2.8.1
PostgreSQL client version	16.2
SpatiaLite version	5.1.0
QWT version	6.3.0
QScintilla2 version	2.14.1
OS version	Windows 10 Version 1903
Active Python plugins
db_manager	0.1.20
grassprovider	2.12.99
MetaSearch	0.3.6
processing	2.12.99

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

It looks like the georeferencing info in the overlapping region is taken form the bottommost Map item instead of the topmost Map item.

I guess this may be due to the fact that

• the items in the QgsPrintLayout object are listed from the topmost to the bottommost
• so the georeferencing information of the Map items are written from the topmost to the bottommost Map item in the composition.xml file which is used by GDAL to actually generate the PDF
• when the PDF is generated by GDAL, the last georeferencing information (the bottommost one) takes precedence in the generated PDF