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Sat Sep 21 08:05:11 2019

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QGIS 3.10 Loves GeoPDF!

Recently, we’ve been working on an exciting development which is coming soon in QGIS 3.10… support for Geospatial PDF exports! This has been a long-desired feature for many QGIS users, and it was only made possible thanks to a group of financial backers (listed below). In this post, we’re going to explore these new features and how they improve your QGIS PDF outputs.

Geospatial PDFs can now be created either by exporting the main QGIS map canvas, or by creating and exporting a custom print layout. For instance, when you select the “Save Map as PDF” option from the main QGIS window, you’ll see a new group of Geospatial PDF related options:

At its most basic, Geospatial PDF is a standard extension to the PDF format which allows for vector spatial datasets to be embedded in PDF files. If the “Include vector feature information” checkbox is ticked when creating a Geospatial PDF output, then QGIS will automatically include all the geometry and attribute information from features visible within the page. So if we export a simple map to PDF, we’ll get an output file which looks just like any old regular PDF map output…

…but, we can also pull this PDF back into QGIS and treat it just like any other vector data source! In the screenshot below we’re using the Identify tool to query on of the polygons and see all the attribute information from the original source layer.

This ability adds a lot of value to PDF exports. Anyone who has ever been supplied a non-spatial PDF as a “spatial dataset” will attest to the frustrations these cause… but if you create proper Geospatial PDFs instead, then there’s no loss of the valuable underlying spatial information or feature attributes! Furthermore, if these PDFs are opened within Acrobat Reader, tools are enabled which allow users to query features interactively.

Another nice benefit which comes with Geospatial PDF output is that layers can be interactively toggled on or off in the PDF viewer. The screenshot below shows a Geospatial PDF file created from a simple QGIS map. On the left we have a list of the layers in the PDF, each of which can be turned on or off inside the PDF viewer!

The really nice thing here is that, thanks to the underlying smarts in the GDAL library which is responsible for the actual Geospatial PDF creation, the PDF renders identically to our original QGIS map. While labels turn on and off alongside their corresponding map layer, they are still correctly stacked in the exact same way as you see in the QGIS window. Furthermore, the created PDFs keep labels and vector features as vector artwork… so there’s absolutely no loss in quality when zooming in to the map! These files look GREAT!

On that same note… the sponsorship allowed us to tackle another related issue, which is that in previous QGIS versions PDF (or SVG) exports would always export every single vertex from any visible feature! Ouch! This meant that if you had a complex polygon boundary layer, you would potentially be creating a PDF with millions of vertices per feature, even though most of these would be overlapping and completely redundant at the exported map’s scale. Now, QGIS automatically simplifies vector features while exporting them (using an appropriate, effectively invisible, level of simplification). The dramatically reduces the created file sizes and speeds up opening them and navigating them in other applications (especially Inkscape). (There’s an option at export time to disable this simplification, if you have a specific reason to!).

Creating Geospatial PDFs from print layouts gives even more options. For a start, whenever a print layout is exported to Geospatial PDFs, we ensure that the created PDF correctly handles stacking of layers alongside any other print layout items you have. In the image below we see a custom print layout which includes interactive layer visibility controls. If a layer is toggled, it’s hidden only from the map item — all the other surrounding elements like the title, north arrow and scalebar remain visible:

That’s not all though! When exporting a print layout to Geospatial PDF, QGIS also hooks into any map themes you’ve setup in your project. If you select to include these themes in your output, then the result is magical! The screenshot below shows the export options for a project with a number of themes, and we’ve chosen to export these themes in the PDF:

Opening the resultant PDF shows that our layer control on the left now lists the map themes instead of individual layers. Viewers can switch between these themes, changing the visibility of layers and their styling to match the QGIS map theme from the project! Additionally, you can even expand out a theme and expose layer-by-layer visibility control. Wow! This means you could create a single PDF output file which includes an environmental, social, cadastral, transport, …. view of your map, all in the one file.

Lastly, there’s even control for fine-tuning the combination of layers which are exposed in the output PDF file and which ones should be toggled on and off together. In the screenshot below we’ve opted to group the “Aircraft” and “Roads” map layers into a single logical PDF group called “Transport”. 

The resultant PDF respects this, showing an entry in the interactive layer tree for “Transport” which toggles both the aircraft and roads layers together:

So there you go — the power of Geospatial PDF, coming your way in QGIS 3.10!

One semi-related benefit of this work is that it gave us an opportunity to rework how “layered” exports from print layouts are created. This has had a significant flow-on impact on the existing ability to create layered SVG outputs from QGIS. Previously, this was a rather fragile feature, which created SVGs with lots of issues – overlapping labels, incorrectly stacked layers, and last-but-not-least, non-descriptive layer names! Now, just like Geospatial PDF exports, the layered SVG exports correctly respect the exact look of your map, and have much more friendly, descriptive layer names:

This should significantly reduce the amount of housekeeping required when working on these layered SVG exports. 

This work was funded by:

  • Land Vorarlberg
  • Municipality of Vienna
  • Municipality of Dornbirn
  • Biodiversity Information Service for Powys and BBNP Local
  • Kanton Zug
  • Canton de Neuchâtel
  • Canton de Thurgovia

North Road are leading experts in extending the QGIS application to meet your needs. If you’d like to discuss how you can sponsor development of features or fixes which you want in QGIS, just contact us for further details!

 

 

Merging PDF documents with imagemagick / convert

Totally unrelated to GIS but a handy tip for linux users out there who want to merge several pdf's into a single document. You can do it from the command line like this:

`` convert -quality 90 -density 300x300 tim_sutton_cv_2010.pdf sam_cv_2010.pdf cvs.pdf``

The quality option is the jpeg compression level to use. The density option is important otherwise the resulting merged pdf will look crappy. Basically it determines the dpi of the output pdf (in my example above I'm putting out a 300dpi document). The merged file size will grow with higher density levels.

Then just give a list (in order of appearance) of pdf's to be merged and the final item in the list is the name of the output pdf.

One gotcha to note: convert rasterises the pdfs so you will no longer be able to select text in the pdf.

If you don't have imagemagick (which provides the convert command line tool) on your system (c'mon its an essential tool!) you can install it like this:

`` sudo apt-get install imagemagick``

Update: After posting this entry, Volker Mische wrote to me recommending pdftk (its in apt) which is easy to use and doesnt rasterise the pdfs when fusing them:

`` pdftk tim_sutton_cv_2010.pdf sam_cv_2010.pdf cat output cvs.pdf``

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