[Layout] Geospatial PDF has slightly incorrect dimensions (e.g. A4: 297 x 210.3 instead of 297 x 210)

[agiudiceandrea]

What is the bug or the crash?

Exporting a layout as Geospatial PDF, the exported PDF may have slightly incorrect dimensions e.g.:

• page size A4 landascape (297mm x 210mm): PDF size 297mm x 210.3mm (instead of 297mm x 210mm) A4L.pdf
• page size A0 portrait (841mm x 1189mm): PDF size 841mm x 1189.2mm (instead of 841mm x 1189mm) A0P.pdf

Steps to reproduce the issue

1. export a layout as a Geospatial PDF with A4 page size
2. open the export PDF with a PDF reader and check the page size

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 issue may be due to the fact that the "page size in PDF units" written in the composition.xml file is rounded using the std::ceil function instead of std::round

QGIS/src/core/qgsabstractgeopdfexporter.cpp

Lines 518 to 525 in f75d66f

	QDomElement width = doc.createElement( QStringLiteral( "Width" ) );
	const double pageWidthPdfUnits = std::ceil( details.pageSizeMm.width() / 25.4 * 72 );
	width.appendChild( doc.createTextNode( qgsDoubleToString( pageWidthPdfUnits ) ) );
	page.appendChild( width );
	QDomElement height = doc.createElement( QStringLiteral( "Height" ) );
	const double pageHeightPdfUnits = std::ceil( details.pageSizeMm.height() / 25.4 * 72 );
	height.appendChild( doc.createTextNode( qgsDoubleToString( pageHeightPdfUnits ) ) );
	page.appendChild( height );

That leads to e.g. an A4 landascape Geospatial PDF having /MediaBox [ 0 0 842 596 ] instead of /MediaBox [ 0 0 842 595 ] or an A0 portrait Geospatial PDF having /MediaBox [ 0 0 2384 3371 ] instead of /MediaBox [ 0 0 2384 3370 ]

See, for reference: "International standard paper sizes in PostScript and PDF"