Viewing posts for the category QGIS
School GIS task: create a 5km COVID-19 lockdown exercise buffer around your house
If you are doing some teaching in the classroom and some online and you are finding "blended teaching" overwhelming, this task is designed for asynchronous self study.
Consuming cloud optimised GeoTIFFs in QGIS Server
QGIS has been able to consume cloud optimised GeoTIFFs (COGs) since v3.2, through the data source manager. This article does not aim to explain what a COG is as various other articles have done so extensively.
Create a custom reference grid in qgis composer part 2
This is a follow-up post on https://kartoza.com/en/blog/create-a-custom-reference-grid-in-qgis-composer/ .
Calculating intersects for map layers and map extent dynamically in QGIS
Recently we have been working on a project that involves simulating the 1 in 50k topographic maps in South Africa. Since we are using QGIS Server to print the map all the logic is set up in print composer. All maps generated are dynamic (users can select a specific area within South Africa to print) and QGIS Server will use the map template to generate the map.
The Longest River in the World
Every now and then there might be a dispute about which is really the longest river in the world. As is shown in this National Geographic article. Even Wikipedia indicates that the fact that the Nile river is accepted as the longest river in the world as "disputed".
FOSS4G 2019 and QGIS in Bucharest
Open source GIS is alive and well and continues to grow in leaps and bounds around the world. Why so many Government entities in South Africa continue paying a fortune of tax-payers money for privative GIS and database software beats me, when wealthy, developed countries (as in most of Europe, for example) saw the light years ago and enthusiastically embrace FOSS.
Show only features within current Atlas feature - QGIS 3
In our endless endeavour to spread QGIS, I was invited to conduct QGIS training at the Surveyor General Department in Swaziland.
Creating a live, topic specific mirror of OpenStreetMap in PostGIS
In this article, we will do a walk-through of creating a live mirror of OSM for a specific country or region and for a specific set of OSM features. For this example, we will fetch all building data for Angola into a PostGIS database, and update that database with new features as they arrive in OSM. Providing an OSM mirror in this way is a powerful tool to pair the power of OSM with the power of QGIS and PostGIS. Now you will be able to do offline analysis of the data in OSM. How does this all work? Here is a little diagram that illustrates the underlying architecture (click for a larger version):
How to make beautiful lollipop call out labels in QGIS
Call out labels are a handy cartographic instrument for attaching labels to features on the map where you want the label to be offset from the feature being labelled. It allows you to prevent the map becoming overcrowded. I call the variant I describe here 'lollipop' labels because the 'callout line' is rendered with a decorative ball at the end.
Using NOTIFY to automatically refresh layers in QGIS
One of the most brilliant but little-known features of QGIS is the ability to trigger layer refreshes and events in response to notifications from PostgreSQL. This was developed by the wizards from Oslandia and is easily added to any existing table in your PostgreSQL database - including PostGIS tables. This feature was added in version 3.0 (see https://qgis.org/en/site/forusers/visualchangelog30/#feature-trigger-layer-refresh-or-layer-actions-from-postgresql-notify-signal). Take for example this simple table:
How to easily add South African and Namibian toposheets as XYZ tiles to QGIS
Thanks to the great work of Grant Slater and the OpenStreetmap team, there are freely available XYZ tilesets for South Africa and Namibia 1:50 000 series toposheets which can easily be added to QGIS. Here is the general procedure to add a layer:
Adding elevation to a line from a DEM in PostGIS and maintaining accurate measures
This is the second in a three part series on the behind-the-scenes GIS work that can go into planning a complex event, in this case the Cape Town Marathon.
How to create a point distance marker layer along a line in PostGIS
This is part 1 of a 3-part series.
QGIS, InaSAFE, OpenStreetMap, and GeoNode in Understanding Risk 2018
Some QGIS 3 Browser Improvements - Small Things Matter
Well, QGIS 3 has been out for a couple of weeks now with lots of new functionality. While you are still feeling your way around all the new features I thought I could highlight some of the improvements to the browser panel that will make you fall further in love with QGIS.
A new plugin to manage land (survey) parcels in QGIS
Kartoza releases the CoGo Plugin for QGIS
Kartoza recently published the CoGo Plugin (aka Parcel Plugin) in the QGIS plugin repository. This plugin expands the group of plugins designed to manage SDI (Spatial Data Infrastructure). CoGo ('coordinate geometry') refers to its ability to handle both types of coordinates used in land surveying, namely cartesian coordinates (x,y; long/lat) and polar coordinates (bearing and distance).
Changing the line direction of line features using the geometry generator in QGIS
I have been playing around with roads layers and wanted to change the line directions for some of my features. I looked around for solutions to do this in QGIS and saw that I could use the swap vector direction plugin in QGIS or ST_reverse in PostgreSQL. But I wanted to find a non destructive way to do this as I did not want to alter my data. I decided to try the geometry generator in QGIS.
How to resolve issues with QGIS 3 Processing Dialog Layouts on MacOS
If you are using QGIS 3 master builds on MacOS and encounter issues with the display of processing dialog layouts like this:
Create a custom reference grid in QGIS composer
If you need to create a reference grid like this for your map, here's a simple method.
Report back on the first QGIS User Conference in Nødebo, Denmark
I finally have some time to sit down and write up some thoughts on the QGIS User Conference and Developer Meeting (aka Hackfest) that we just held in Nødebo, Denmark. First up I need to thank Lene Fischer, who was the organiser and wowed us all with her relaxed and competent organisational approach to the conference. Thanks also to the University of Copenhagen School of Forestry - they sponsored the event by providing the venue and accommodation - and the venue was absolutely awesome with little cottages in the forest and all sorts of interesting diversions scattered around the forest. Lene gave me a list of names of people who helped to organise the event - I am sorry I have only got your first names but a very big thank you to you all!