Recently I was invited by the colleagues from OpenGIS.ch to lend a hand in a training session about QGIS server.

This was a good opportunity to update my presentation for QGIS3, to fix a few bugs and to explore the powerful capabilities of QGIS server and Python.

As a result, I published the full recipe of a Vagrant VM on github: https://github.com/elpaso/qgis3-server-vagrant

The presentation is online here: http://www.itopen.it/bulk/qgis3-server/

What’s worth mentioning is the sample plugins (I’ll eventually package and upload them to the official plugin site):

• XYZ: add simple XYZ tile server, ready to use within QGIS XYZ connections: https://github.com/elpaso/qgis3-server-vagrant/tree/master/resources/web/plugins/xyz
• custom service, does nothing but shows how to create a Python custom service by exploiting the new service capabilities available in QGIS3: https://github.com/elpaso/qgis3-server-vagrant/tree/master/resources/web/plugins/customservice
• HTTP Basic auth (how to add your auth scheme to QGIS server): https://github.com/elpaso/qgis3-server-vagrant/tree/master/resources/web/plugins/httpbasic
• more …

The VM uses 4 different (although similar) deployment strategies:

• good old Apache + mod_fcgi and plain CGI
• Nginx + Fast CGI
• Nginx + standalone HTTP Python wrapped server
• Nginx + standalone WSGI Python wrapped server

Have fun with QGIS server: it was completely refactored in QGIS 3 and it’s now better than ever!

# Assuming your subnet is 192.168.9

nmap -p 6000 192.168.1.*

Nmap scan report for android-8899989888d02271.homenet.telecomitalia.it (192.168.99.50)
Host is up (0.0093s latency).
PORT STATE SERVICE
6000/tcp open X11

• the future of processing providers: should they be part of QGIS code or handled independently as plugins?
• the road forward to a better bug reporting system and CI platform: move to gitlab?
• the certification program for QGIS training courses: how (and how much) training companies should give back to the project?
• SWOT analysis of current QGIS project: very interesting discussion about the status of the project.
• QGIS Qt Quick modules for mobile QGIS app

• How to set up a development environment and make your first pull request
• How to write tests for QGIS (in both python and C++)

Did you know that the possibilities to make a full QGIS back end solution for quality assurance and archiving in PostgreSQL are immense? SQL has it’s well known limitations, but with a little bit creativity you can make quite nice solutions just using triggers and rules. In this post I’ll explain what we did lately based on a project with a customer. He needed to assure the consistency of data but still give his employees the possibility of a fast feeding of the data collected on the field to the database. Another request was to keep every status of the data with the information about the changes (archiving). It’s always the question, where to put the logical part of the solution. QGIS is quite powerful with constraints, but the undeniable advantage of a back end solution is, that you can use any front end - no matter what configuration you have on QGIS or what Feature Manipulation Engine (FME) you use - without influencing the guarantee of data validity.

Situation

It’s all about trees

At least for that customer we got lately. The customer owns pieces of land all over Switzerland. On this pieces are forests and in the forests are - as expected - trees. Well, mostly - if you are not a bark beetle or a squirrel - you don’t care about a single tree. Except if there is something special with it. For example, a branch that could fell down on your brand new Citroën DS or if the tree has a disease that could kill the whole forest, that is actually needed to convert the carbon dioxide (from your DS) into oxygen. The issuetrees (yellow) lie on the forest (green) - and the forest lies on the land piece (brown). And the (Entity Relationship Model) ERM looks like this. A land can have zero, one or more forests - and a forest can have zero, one or more trees with issues.

It’s not really about trees

The situation is, that a lot of field workers (so called tree-inspectors) work with our mobile solution QField, where they can collect the data while standing in the middle of a wild forest with one foot in a rabbit hole and the other one in the stinging nettle. It’s quite possible and usual that there can be some problems entering all the data correctly. Typing issues on the tablet while running away from wolves or just lack of concentration because of the beauty of the swiss forests.

And it’s about lots of front ends

But there are not only the tree-inspectors. There are the office-clerks working with QGIS and planning, when the problems on the tree has to be solved. And finally there are the woodsmen solving the issues and setting the status to done on QField again. So there have to be a lot of projects using the same data but with different configurations. If you make all the quality assurance on the front end you won’t have time to care about the trees anymore and beside of that it’s fault-prone.

Quality assurance in the back end

Data integrity with constraint functions

There are simple constraints like that a field is not empty and more complex constraints with a lot of logic regarding the content of the field.

Simple constraints

Lots of data integrity issues can be solved by using simple constraints like NOT NULL (column must not assume null), UNIQUE (column must be unique among all the rows in table) or Primary Key and Foreign Keys constraints.

CREATE TABLE live.issuetree (
  issuetree_id integer UNIQUE NOT NULL,
  gps_id text NOT NULL,
  issue text,
  assignee text,
  done boolean,
  donedate date,
  forest_id NOT NULL,
  CONSTRAINT issuetree_pkey PRIMARY KEY (issuetree_id),
  CONSTRAINT forest_fkey FOREIGN KEY (forest_id) REFERENCES live.forest;
);

Checks and constraint functions

For more special cases or not really technical constraints, we can use checks. Here for example: If the issue is done, then it needs to have a donedate. But not if done is not TRUE (NULL or FALSE).

CHECK (done IS NOT TRUE OR donedate IS NOT NULL )

And if these cases are more complex and not technical at all, we can put it to a function and use the return value (for example the error message) as condition. In the following example we want to assure that assignee is the name of one of the employed woodsmen. Of course it can be NULL too.

CONSTRAINT chk_assignee_valid CHECK (live.chk_assignee_valid(assignee) = ''::text)

And the function live.chk_assignee_valid:

CREATE OR REPLACE FUNCTION live.chk_assignee_valid(a_assignee text ) RETURNS text
LANGUAGE plpgsql AS $$
DECLARE
result text;
BEGIN
  IF (
    SELECT TRUE
    WHERE a_assignee NOT IN ( 'Fritz Fangorn' ,  'Fiona Finglas',  'Fred Fladrif', 'Barbara Beechbone', 'Berthold Bregalad' )
          AND a_assignee IS NOT NULL
  ) THEN
    result='The assignee has to be one of these guys: Fritz Fangorn, Fiona Finglas, Fred Fladrif, Barbara Beechbone, Berthold Bregalad';
    RAISE EXCEPTION '%', result;
  ELSE
    RAISE NOTICE 'CHECK chk_assignee_valid SUCCESSFUL';
    result='';
  END IF;
  RETURN result;
END;

So with many of these constraints, we can assure a lot and the data are fully correct. But this is not always comfortable to use. Why? Go on reading…

Using of a “data quarantine”

Let’s imagine that the tree-inspector collected all day data in QField. Standing in the middle of the mentioned stinging nettle and rabbit holes, running from wolves etc… Of course he made some mistakes while collecting data. In the evening he returns tired to the office, already thinking about the dinner meal his wife is cooking (or his husband, of course), and wants to upload the data from the QField project to the database. And what happens? Lot’s of error messages. He thinks about to solve them tomorrow, because his wife (or his husband) can get quite angry when he is late for dinner. But if he does it tomorrow, the data are only stored on the device and nowhere else overnight. He need to have them in the database. No matter, if correct or not. And this leads to the idea of the “data quarantine”.

Use Case

All data entered to the database (valid or not) need to be stored. The entries accepted from the so called live tables with all constraints, are stored normally. The entries failed because of the constraint, are stored in another table. In the so called quarantine table. So you have for every live table another quarantine table. This means, we need another table structure existing parallel to the live tables. We do it in two schemas: The live schema and the quarantine schema. So the tree-inspector synchronizes his QField without any problem to the database. The correct entries are written into the live tables. The incorrect into the quarantine. Actually all the data are coming into the quarantine and there is a Trigger passing them through to the live table. If they success, they will be stored in live and removed from quarantine. Otherwise they keeps staying in the quarantine. Same situation when the quarantine-clerk later corrects the data entries in the quarantine. On an update they are pushed into the live-table. If success, all good. Otherwise the entry keeps staying in the quarantine.

Structure

And how we do that?

It’s all solved by using triggers. SQL triggers are procedural code that are automatically executed on an action on a table or view. For this solution we actually need two trigger per quarantine table. After insert into or update quarantine table, a trigger should be fired for every entry, doing this: Insert the same entry into the live table. If success, then delete the entry in the quarantine table. Else write the info to the current entry in the quarantine table. Probably you noticed the problem with the recursion, but let’s not think about it at the moment :-)

Code

In PostgreSQL we can use trigger functions. Means you have the triggers on the table calling the functions.

Trigger on table quarantine.issuetree after update

CREATE TRIGGER pushtolive
AFTER UPDATE
ON quarantine.issuetree
FOR EACH ROW
EXECUTE PROCEDURE quarantine.pushtolive();

Trigger function (simplified)

CREATE OR REPLACE FUNCTION quarantine.pushtolive() RETURNS trigger AS $BODY$
BEGIN
  INSERT INTO live.issuetree
  SELECT * FROM quarantine.issuetree
  WHERE quarantine_serial = NEW.quarantine_serial
  RETURN NEW;
END; $BODY$
LANGUAGE plpgsql;

Trigger function used for the solution when inserting into live

And this is the function with the logical part with success and failing.

CREATE OR REPLACE FUNCTION quarantine.pushtolive() RETURNS trigger AS $BODY$
BEGIN
-- insert into live
INSERT INTO live.issuetree
SELECT * FROM quarantine.issuetree
WHERE quarantine_serial = NEW.quarantine_serial
RAISE NOTICE 'Inserted row in live.issuetree';
-- delete in quarantine
DELETE FROM quarantine.issuetree
WHERE quarantine_serial = NEW.quarantine_serial
RAISE NOTICE 'Deleted row in quarantine.issuetree';
-- return when here
RETURN NEW;
-- if it failed:
EXCEPTION WHEN OTHERS THEN
  RAISE NOTICE 'EXCEPTION: %', SQLERRM;
  UPDATE quarantine.issuetree
  SET fail_info = SQLERRM,
  WHERE NEW.quarantine_serial = quarantine_serial;
  RAISE NOTICE 'Updated row in quarantine.issuetree';
  RETURN NEW;
END; $BODY$

As you can see, we use here an id called quarantine_serial. We can not use the primary key in the quarantine, because here everything is accepted and so nothing of the entered data (not even issuetree_id) has to be be unique. But to identify the entry in the quarantine table we create the serial quarantine_serial.

Trigger function used for the solution when inserting into or update live

Actually the trigger function before is not usable. Because it works only to insert new data into the live system. Now we remember the use case. The trigger here in the quarantine does not know if the tree-inspector created a new issuetree or updated an old one. On synchronization he made an INSERT INTO to the quarantine with all entries. But these could be new entries (new trees) or already existing ones in the live table. So the trigger function has to decide, if it’s an insert or an update on the live table.

CREATE OR REPLACE FUNCTION quarantine.pushtolive() RETURNS trigger AS $BODY$
BEGIN
-- check if an entry with this id is already existing
IF( SELECT TRUE FROM live.issuetree WHERE issuetree_id = NEW.issuetree ) THEN
  -- update into live
  UPDATE live.issuetree
  SET gps_id = NEW.gps_id, issue = NEW.issue, assignee = NEW.assignee, done = NEW.done, date = NEW.date, forest_id = NEW.forest_id
  WHERE issuetree_id = NEW.issuetree_id
  RAISE NOTICE 'Updated row in live.issuetree';
ELSE
  -- insert into live
  INSERT INTO live.issuetree ( issuetree_id, gps_id, issue, assignee, done, date, forest_id )
  VALUES ( NEW.issuetree_id, NEW.gps_id, NEW.issue, NEW.assignee, NEW.done, NEW.date, NEW.forest_id )
  RAISE NOTICE 'Inserted row in live.issuetree';
END IF;
-- delete in quarantine
DELETE FROM quarantine.issuetree
WHERE quarantine_serial =NEW.quarantine_serial
RAISE NOTICE 'Deleted row in quarantine.issuetree';
-- return when here
RETURN NEW;
-- if it failed:
EXCEPTION WHEN OTHERS THEN
  RAISE NOTICE 'EXCEPTION: %', SQLERRM;
  UPDATE quarantine.issuetree
  SET fail_info=SQLERRM,
  WHERE NEW.quarantine_serial = quarantine_serial;
  RAISE NOTICE 'Updated row in quarantine.issuetree';
  RETURN NEW;
END; $BODY$

Recursion problem

The problem with the recursion is that we have a trigger after update of table issuetree in quarantine. This trigger calls the function, and the function (in case of fail updating live) updates the quarantine.issuetree with the error-message. So there is another update and the trigger is fired again, and again, and again… ♪Across the universe♬ We could solve the problem by checking the depth of triggers in PostgreSQL:

CREATE TRIGGER pushtolive AFTER UPDATE ON quarantine.issuetree
FOR EACH ROW
WHEN pg_trigger_depth() = 0
EXECUTE PROCEDURE quarantine.pushtolive();

And it looks like this

The yellow points are the issue trees in the live. If we create another one and have a mistake in it (GPS Id wrong), then it’s stored in the quarantine (pink). When we correct the data it’s written over the quarantine trigger into live. If succeeded, the point changes the color to yellow. Actually the yellow point appears (live) and the pink point(quarantine) disappears, because the entry is inserted into live and deleted in quarantine.

Archiving all data

There are different reasons why you need to archive data. Maybe somewhen you want to show your grandchildren, how much forest we still had today before the sky got dark. But this was not the reason for the mentioned customer, but legal reasons: When the woodsman cuts the last bamboo tree of the forest and this was the only food for the very last living panda bear of Switzerland, we need to know who created or changed this entry in the database and what tree should have been chopped down instead.

Third schema “archive”

So we created a third schema parallel to live and quarantine. The archive schema. This means every table in live does not only have a quarantine table accordingly, but also an archive table too where all the old status of entries including the timestamp, when it has been archived. Of course not only the changed live data are stored in the archive, but also every changed data from quarantine.

Use Case 1

The tree-inspector enters an entry of an issue tree that already existed in the live table to the quarantine (1). The after insert trigger is fired and it tries to write to the live table. And with success. The entry is written to the live table (2). This means, before the entry in live is updated, the old one was copied to the archive table (3). Then in the same transaction the entry in the quarantine is deleted (1). Means the old status is copied to the archive too (4). So there will be the updated entry in the live-table (2), no entry in the quarantine-table (1) and two entries (3 and 4) in the archive table.

Use Case 2

The tree-inspector enters an entry of an issue tree that already existed in the live table to the quarantine (1). The after insert trigger is fired and it tries to write to the live table. And it fails. The entry in the quarantine will be updated with the error-message (2). The old status is copied to archive (1). The office clerk makes no the changes to this entries. The trigger is fired and this time it could write into the live-table with success (3). So the old entry is copied to the archive (4) and after deleting the entry in the quarantine, there will be the second old status of quarantine (5) in archive too. So there will be the updated entry in the live-table (3), no entry in the quarantine-table (1 and 2) and three entries (1, 4 and 5) in the archive table.

Structure

And how we do that?

It’s solved by using triggers too. We actually need only one trigger per table, but not only in quarantine, but also in live. It has to be fired before every update of every entry, doing this: Insert a copy of the current entry into the archive table with the status it had until the update we are doing right now.

Code

It’s the same code for the live and the quarantine table triggers. So only the ones for the quarantine are explained.

Trigger on table quarantine.issuetree before update

CREATE TRIGGER archiving
BEFORE UPDATE
ON quarantine.issuetree
FOR EACH ROW
EXECUTE PROCEDURE quarantine.archiving();

Trigger Function (simplified)

CREATE OR REPLACE FUNCTION quarantine.archiving() RETURNS trigger AS $BODY$
BEGIN
  INSERT INTO archive.issuetree
  SELECT *
  FROM quarantine.issuetree
  WHERE NEW.quarantine_serial = quarantine_serial;
END; $BODY$
LANGUAGE plpgsql;

And the archive-tables have a default time-column to store the time, when the entry has been archived:

ar_time timestamp without time zone DEFAULT now()

That’s it

That’s what I just needed to tell you. It was a very interesting project and I liked working on it. Thanks for reading so far. If you have questions, improvement suggestions or anything else to tell me, then please comment it. See yah! :-)

./configure -prefix /opt/qt593 -debug -opensource -confirm-license -ccache -platform linux-clang

make -j9
sudo make install

/opt/qt593/bin/qmake WebKit.pro
make -j9
sudo make install

/opt/qt593/bin/qmake qscintilla.pro
make -j9
sudo make install

/opt/qt593/bin/qmake qwt.pro
make -j9
sudo make install

You may have seen my earlier tutorial where I described how to make nice looking hillshaded maps in QGIS using SRTM elevation data. Well, we don’t have to stop with just one hillshade layer on a map, it is possible to overlay multiple hillshades; a procedure that can increase the visual quality and detail. The following image is the hillshade we made before. Once you re-create a hillshade, following the previous tutorial, you can head to the next step (note that brightness and contrast settings may be different due to changes in how QGIS generates and displays hillshades).

We can improve the SRTM hillshade further by adding ESRI’s World Hillshade layer, which uses multi-directional illumination (also called a Swiss Hillshade in tribute to the celebrated Swiss cartographer Eduard Imhof). In addition, World Hillshade has a much higher resolution than SRTM 30m data in some regions of the world, it is 2m for most of the England and Wales, 10m for most of the US, 5m for Spain and 3m for Holland etc. The only drawback is that the style of this layer is somewhat controversial, some love it, some hate it, it looks like it’s illuminated from above, but mixing it with the SRTM hillshade obviates some of it criticised flaws.

To add the World Hillshade layer in QGIS go to the Layer Menu – Add Layer – Add ArcGIS MapServer Layer – click New and add the following URL:

https://services.arcgisonline.com/arcgis/rest/services/Elevation/World_Hillshade/MapServer

Notice QGIS 2.18 no longer needs a plugin to add ESRI layers, it new has this functionality built in. Also, open the url in a browser such as Firefox, it brings up a webpage that describes the layer. We also see links to other other layers. Yes, they can all be added to QGIS by simply taking the URL of the webpage that describe the layer and connecting to it via the ArcGIS MapServer Layer connector.

Name the layer World Hillshade and click Connect, then click and highlight the layer it connects to. Finally, click the Add button to add the layer to the canvas.

Next, we need to adjust the properties of the World Hillshade layer to properly overlay it above the SRTM hillshade layer. Make sure the World hillshade layer is the topmost layer. In the Layers Panel, right click Layer properties and in the window that opens up, click Style (if not visible). Next, change the Layer Blending mode (under color rendering) to Overlay. Adjust the layer’s brightness to around -20 and leave contrast at 0. If you find the scene is still too dark, brighten the SRTM Hillshade by increasing the layer’s brightness. You may also have to change (lower) the Min value of the Min – Max value boxes. Leave the contrast at 0 for the SRTM hillshade. Also, don’t brighten it too much as it might become washed out, loose detail, especially in bright areas. Play around the controls, settings may vary depending on the SRTM data you download and the version of QGIS you use.

Here’s a comparison in Ireland, a ring like structure of hills with a central peak. No, it’s not a meteorite crater. It’s a different kind of geological marvel, the Slieve Gullion Complex and its ring dyke; the deeply eroded remains of a 410 million year old Caledonian volcano. The SRTM hillshade is on the left and World Hillshade + SRTM hillshade is on the right (click on the image, it’s best appreciated full size):

We can see the World Hillshade + SRTM Hillshade layer shows much finer detail. We see a parallel array of roughly north-south orientated lines, these are fractures and faults that cut the Slieve Gullion Complex that were perhaps enhanced by glacial erosion. Also, look carefully, there seems to be some roads meandering across the landscape (hint, bottom of the map and right of the scale bar). You should get even better results with higher resolution World Hillshade data. We also notice that bending SRTM derived hillshade with World Hillshade adds a naturalistic illumination not apparent in multi-directional hillshading. So we have the best of both worlds, a high resolution hillshade and realistic looking illumination.

Hope you found this tutorial helpful.

References:

Baxter, S., 2008. A Geological Field Guide to Cooley Gullion, Mourne & Slieve Croob [pdf]. Geological Survey of Ireland, Dublin. p. 43-53.

Geologists display the dip and strike of rock layers on geological maps using a dip and strike symbol, where dip in degrees indicates the maximum angle a rock layer descends relative to the horizontal. However, it is not directly possible in QGIS 2.18, using basic label settings, to place and orient a dip label next to a dip and strike symbol.

However, there is a way around this issue using Trigonometry and editing the layer’s Attribute Table. This method may be useful for controlling the position and orientation of labels around point features in general. The first step involves adding values to the Attribute Table. First, add these two new columns:

• Angle – 0° is North and values increases clockwise up to 359°
• Distance – label distance from a point feature

You can add Angle and Distance values to these columns manually or use the Field Calculator (see below) to add values if you have lots of points. Also, I chose Map Units (not millimeters) for Symbol Size, Font Size and Distance for my map, as I prefered to keep symbol size, font size and position of labels fixed when zooming in and out.

Note – I use Strike (Angle) and Label Distance (Distance)  in my Attribute Table

The next step is to control the position of the label around the points using trigonometry. Right click the points layer and choose:

Properties – Labels – Placement

Check that Offset From Point is checked and then click the Data Defined Override next to the Offset X, Y boxes and choose Edit. The Expression String Builder will appear. Enter the following expression in the Expression String Builder window:

to_string ( ((-1) * ( “Distance” )) * cos ( radians ( “Angle” ))) ||’,’|| to_string (((-1) * ( “Distance” )) * sin ( radians ( “Angle” )) )

The expression takes the angle and distance values from the Attribute Table (edited earlier) and calculates an X, Y label position relative to the point feature. You may also optionally control the angle of a symbol or icon itself via:

Layer Properties – Style – click Data Defined Override icon – Edit

Then enter the following expression in the Data Defined Override dialogue:

“Angle” – 90

Finally, to control the rotation of label text, so text follows the orientation (angle) of a rotating symbol or icon, choose:

Layer Properties – Labels – Placement – Data Defined – Rotation

Click the Data Defined Override Icon again and then choose Edit. Enter the following expression in the Data Defined Override dialogue:

(“Angle” – 90) * -1

The following geological map of the Old Head of Kinsale in southern Ireland shows the results of the above procedure. We see that the dip labels rotate and currently follow the orientation of the dip and strike symbols (note that the points are at the intersection of the T symbol).

Geological Survey of Ireland – Creative Commons Attribution 4.0 license

You may have several different symbols, of various sizes, each requiring an appropriate label distance expressed in the Attribute Table. It took me a few tries before I found the right distances for my geological symbols, from 90 to 230 meters distance depending on the symbol size and type.

Lastly, the expressions “Angle” – 90 and (“Angle” – 90) * -1 were necessary in my case because I needed to place my labels next to the dip and strike symbol’s barb. You may need to use a different expression e.g. “Angle” and (“Angle”) * -1, or a value other than 90° depending on the symbol used and the prefered label placement location. Some trial and error is may be required to find the correct label position.

• fixed some bugs and feature requests on the official QGIS plugin repo that I’m maintaining since the very beginning
• make the QGIS official plugin repository website mobile-friendly
• QGIS Server Python Plugin API refactoring, I’ve completed the work on the new API, thanks to the ongoing server refactoring it’s now much cleaner than it was in the first version
• attribute table bugs: I started to address some nasty bugs in the attribute table, some of those were fixed during the week right after the hackfest
• unified add layer button, we had a productive meeting where we decided the path forward to implement this feature, thanks to Boundless that is funding the development, this feature is what’s I’m currently working on these days

Last week we kicked off the first (of hopefully many) Australian QGIS hackfests Developers Meetings. It was attended by 3 of the core QGIS development team: Nathan Woodrow, Martin Dobias and myself (Nyall Dawson), along with various family members. While there’s been QGIS hackfests in Europe for over 10 years, and others scattered throughout various countries (I think there was a Japanese one recently… but Twitter’s translate tool leaves me with little confidence about this!), there’s been no events like this in the Southern hemisphere yet. I’ve been to a couple in Europe and found them to be a great way to build involvement in the project, for both developers and non-developers alike.

In truth the Australian hackfest plans began mostly an excuse for Nathan and I to catch up with Martin Dobias before he heads back out of this hemisphere and returns to Europe. That said, Nathan and I have long spoken about ways we can build up the QGIS community in Australia, so in many ways this was a trial run for future events. It was based it in Noosa, QLD (and yes, we did manage to tear ourselves away from our screens long enough to visit the beach!).

Nathan Woodrow (@NathanW2), myself (@nyalldawson), and Martin Dobias (@wonder-sk)

Here’s a short summary of what we worked on during the hackfest:

• Martin implemented a new iterator style accessor for vertices within geometries. The current approach to accessing vertices in QGIS is far from optimal. You either have the choice of an inefficient methods (eg QgsGeometry.asPolyline(), asPolygon(), etc) which requires translations of all vertices to a different data structure (losing any z/m dimensional values in the process), or an equally inefficient QgsAbstractGeometry.coordinateSequence() method, which at least keeps z/m values but still requires expensive copies of every vertex in the geometry. For QGIS 3.0 we’ve made a huge focus on optimising geometry operations and vertex access is one of the largest performance killers remaining in the QGIS code. Martin’s work adds a proper iterator for the vertices within a geometry object, both avoiding all these expensive copies and also simplifying the API for plugins. When this work lands traversing the vertices will become as simple as

for v in geom.vertices():
   ... do something with the vertex!

• Martin is also planning on extending this work to allow simple iteration over the parts and rings within geometries too. When this lands in QGIS we can expect to see much faster geometry operations.
• Nathan fixed a long standing hassle with running standalone PyQGIS scripts outside of the QGIS application on Windows. In earlier versions there’s a LOT of batch file mangling and environment variable juggling required before you can safely import the qgis libraries within Python. Thanks to Nathan’s work, in QGIS 3.0 this will be as simple as just making sure that the QGIS python libraries are included in your Python path, and then importing qgis.core/gui etc will work without any need to create environment variables for OSGEO/GDAL/PLUGINS/etc. Anyone who has fought with this in the past will definitely appreciate this change, and users of Python IDEs will also appreciate how simple it is now to make the PyQGIS libraries available in these environments.
• Nathan also worked on “profiles” support for QGIS 3.0. This work will add isolated user profiles within QGIS, similar to how Chrome handles this. Each profile has it’s own separate set of settings, plugins, etc. This work is designed to benefit both plugin developers and QGIS users within enterprise environments. You can read more about what Nathan has planned for this here.
• I continued the ongoing work of moving long running interface “blocking” operations to background tasks. In QGIS 3.0 many of these tasks churn away in the background, allowing you to continue work while the operation completes. It’s been implemented so far for vector and raster layer saving, map exports to images/PDF (not composers unfortunately), and obtaining feature counts within legends. During the hackfest I moved the layer import which occurs when you drag and drop a layer to a destination in the browser to a background task.
• On the same topic, I took some inspiration from a commit in Sourcepole’s QGIS fork and reworked how composer maps are cached. One of my biggest gripes with QGIS’ composer is how slow it is to work with when you’ve got a complex map included. This change pushes the map redrawing into a background thread, so that these redraws no longer “lock up” the UI. It makes a HUGE difference in how usable composer is. This improvement also allowed me to remove those confusing map item “modes” (Cache/Render/Rectangle) – now everything is redrawn silently in the background whenever required.
• Lastly, I spent a lot of time on a fun feature I’ve long wanted in QGIS – a unified search “locator” bar. This feature is heavily inspired by Qt Creator’s locator bar. It sits away down in the status bar, and entering any text here fires up a bunch of background search tasks. Inbuilt searches include searching the layers within the current project (am I the only one who loses layers in the tree in complex projects!?), print layouts in the project, processing algorithms, and menu/toolbar actions. The intention here is that plugins will “take over” and add additional search functionality, such as OSM place names searching, data catalog searches, etc. I’m sure when QGIS 3.0 is released this will quickly become indispensable!

The upcoming QGIS 3.0 locator bar

Big thanks go out to Nathan’s wife, Stacey, who organized most of the event and without whom it probably would never have happened, and to Lutra Consulting who sponsored an awesome dinner for the attendees.

We’d love this to be the first of many. The mature European hackfests are attended by a huge swath of the community, including translators, documentation writers, and plugin developers (amongst others). If you’ve ever been interested in finding out how you can get more involved in the project it’s a great way to dive in and start contributing. There’s many QGIS users in this part of the world and we really want to encourage a community of contributors who “give back” to the project. So let Nathan or myself know if you’d be interested in attending other events like this, or helping to organize them locally yourself…

A lot of cartographers have a love/hate relationship with label halos. On one hand they can be an essential technique for improving label readability, especially against complex background layers. On the other hand they tend to dominate maps and draw unwanted attention to the map labels.

In this post I’m going to share my preferred techniques for using label halos. I personally find this technique is a good approach which minimises the negative effects of halos, while still providing a good boost to label readability. (I’m also going to share some related QGIS 3.0 news at the end of this post!)

Let’s start with some simple white labels over an aerial image:

These labels aren’t very effective. The complex background makes them hard to read, especially the “Winton Shire” label at the bottom of the image. A quick and nasty way to improve readability is to add a black halo around the labels:

Sure, it’s easy to read the labels now, but they stand out way too much and it’s difficult to see anything here except the labels!

We can improve this somewhat through a better choice of halo colour:

This is much better. We’ve got readable labels which aren’t too domineering. Unfortunately the halo effect is still very prominent, especially where the background image varies a lot. In this case it works well for the labels toward the middle of the map, but not so well for the labels at the top and bottom.

A good way to improve this is to take advantage of blending (or “composition”) modes (which QGIS has native support for). The white labels will be most readable when there’s a good contrast with the background map, i.e. when the background map is dark. That’s why we choose a halo colour which is darker than the text colour (or vice versa if you’ve got dark coloured labels). Unfortunately, by choosing the mid-toned brown colour to make the halos blend in more, we are actually lightening up parts of this background layer and both reducing the contrast with the label and also making the halo more visible. By using the “darken” blend mode, the brown halo will only be drawn for pixels were the brown is darker then the existing background. It will darken light areas of the image, but avoid lightening pixels which are already dark and providing good contrast. Here’s what this looks like:

The most noticeable differences are the labels shown above darker areas – the “Winton Shire” label at the bottom and the “Etheridge Shire” at the top. For both these labels the halo is almost imperceptible whilst still subtly doing it’s part to make the label readable. (If you had dark label text with a lighter halo color, you can use the “lighten” blend mode for the same result).

The only issue with this map is that the halo is still very obvious around “Shire” in “Richmond Shire” and “McKinlay” on the left of the map. This can be reduced by applying a light blur to the halo:

There’s almost no loss of readability by applying this blur, but it’s made those last prominent halos disappear into the map. At first glance you probably wouldn’t even notice that there’s any halos being used here. But if we compare back against the original map (which used no halos) we can see the huge difference in readability:

Compare especially the Winton Shire label at the bottom, and the Richmond Shire label in the middle. These are much clearer on our tweaked map versus the above image.

Now for the good news… when QGIS 3.0 is released you’ll no longer have to rely on an external illustration/editing application to get this effect with your maps. In fact, QGIS 3.0 is bringing native support for applying many types of live layer effects to label buffers and background shapes, including blur. This means it will be possible to reproduce this technique directly inside your GIS, no external editing or tweaking required!