Common Printing Bugs In Qgis And Potential Fixes

Identifying the Printing Bug

As a powerful open source geographic information system (GIS) software, QGIS offers robust map printing capabilities for users. However, common bugs in the print process may impact your ability to generate high-quality printed outputs. Detecting the type of printing issue is the first step towards corrective fixes.

Key clues to the QGIS printing bug include:

• Blank print preview screen
• Missing map elements when printing (layers, labels, legends, scalebar etc.)
• Incorrect scalebar on printed map

Once you have identified the specific QGIS printing error, you can proceed to implement the appropriate fixes as outlined in this guide. For example, a blank print preview which fails to render any map elements often requires plugin updates for settings to propagate properly. Missing layers or scalebars, on the other hand, stem from underlying code issues interacting with the Print Composer.

Blank Print Preview Screen

A blank print preview screen that shows none of your QGIS map elements is a common bug due to versioning issues, outdated plugins or plugin conflicts.

Fix: Update Print Composer Plugins

When encountering a blank preview, the first troubleshooting step is updating key plugins that interact with the QGIS Print Composer:

1. Open the Plugin Manager from the QGIS menu Plugins > Manage/Install Plugins
2. Check for updates on plugins like PrintLayout Plugin, Georeferencer GDAL, AtlasPrint Plugin
3. Install available updates and restart QGIS after plugins finish updating

Updating plugins resolves many conflicts that may prevent your map settings, layers and elements from properly propagating to the print preview and PDF. For specific plugins like Atlas Print, also check the plugin configuration settings after updating.

Additional Fixes

If updating plugins does not address the blank print preview, try additional troubleshooting steps:

• Disable any third-party plugins that impact printing
• Verify map item layer sources are valid without broken paths or links
• Reset QGIS configuration and layout template settings

As a last resort, a fresh install of QGIS may eliminate complex software conflicts causing blank print jobs.

Missing Map Elements When Printing

A common printing frustration is seeing certain layers, labels, scale bars, north arrows and other map elements vanish when generating the physical or PDF output in QGIS Print Composer.

Fix: Check Layer Visibility Settings

The leading cause of missing map elements lies in underlying visibility rules at the layer level in Print Composer:

1. Open the layer styling panel, go to the Source tab and verify the data source
2. In the layer Properties > Rendering menu, validate visibility rules for “Printing” vs “Screen”
3. Ensure the layer is toggled as visible for map outputs by checking “Printing” under Rendering

Unlike the QGIS map canvas, layers have separate visibility settings that control printing – so elements may disappear if print visibility rules are disabled mistakenly.

Additional Fixes

Other aspects to verify when dealing with missing map items:

• Validate layout settings to confirm Print Composer is set to export layers symbology and labels
• Check that the data frame Item Properties has correct extents to cover layers
• Toggle auxiliary components like north arrow, legend, labels “off” and “on”

Incorrect Scalebar on Printed Map

A scalebar improperly calibrated to your QGIS project units and resulting in inaccurate printed map scales is another common occurrence.

Fix: Re-add and Configure Scalebar

To correctly set the scalebar for print outputs:

1. Delete existing scalebar instances in Print Layout
2. Add a new scalebar, right-click and open Item Properties
3. In Properties, go to Scalebar > Style & configure extent units to match Project properties
4. Preview the print re-check scalebar units vs printed map scale

Resetting the scalebar to sync its units and style with the current QGIS project corrects issues with incorrect scales on exported PDFs or paper maps.

Additional Scalebar Fixes

Other aspects to validate for correcting scalebar bugs:

• Scalebar segments settings match numbering format for project CRS units
• Project on-the-fly reprojection discrepancies fixed
• Layout data frame units synchronized with map units

Exporting vs Printing in QGIS

Exporting QGIS layouts to georeferenced PDFs can avoid certain printing bugs and provides greater customization control over high resolution outputs to share or publish online:

Code: Export Map to PDF

To programmatically export a print layout as a PDF from PyQGIS:

layout = QgsProject.instance().layoutManager().layoutByName('Layout1')
exporter = QgsLayoutExporter(layout)
pdf_path = '/Path/for/PDF.pdf' 
exporter.exportToPdf(pdf_path, QgsLayoutExporter.PdfExportSettings()) 

Key parameters:

• layout: QgsLayout instance
• exporter: QgsLayoutExporter (sets layout for export)
• pdf_path: File path to save PDF
• PdfExportSettings: Settings like DPI, rasterization settings etc.

Customizing and exporting QGIS print jobs allows bypassing certain native printing system conflicts.

Additional QGIS Print Troubleshooting Tips

Further techniques to troubleshoot QGIS printing errors:

• Preview layout draft prints before sending final job
• Use up-to-date LTR version for increased stability
• Leverage community forums like Stack Exchange to find fixes
• Ensure print jobs have sufficient memory/resource allocation
• Disable complex layer styles, auxiliary components first

Applying fixes like updating plugins, checking visibility rules, resetting scalebars and custom code exports will resolve the most common QGIS printing bugs – but do tap into the wider QGIS user community for additional troubleshooting advice.