Calculating area of rasters in QGIS
QGIS raster functionality has come a long way and continues to improve. During my spare time, I am always on the lookout for interesting questions posed on https://gis.stackexchange.com.
Speeding up multiple web map service requests using Python's asyncio and aiohttp
Geocontext is a Django app that retrieves information from multiple web based services for a specific query point. The services are arranged into hierarchies with multiple services in a group and multiple groups in a collection. It currently supports querying WMS, WFS & ArcREST services.
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.
Does hosting your own server still make sense in 2020?
- Some governments (e.g. Canada, Indonesia, others) have legislated that government datasets must be hosted on servers within the physical borders of the country. My response to this is usually to seek our local cloud providers. For example, Amazon has data centers in Canada that may be used for the Canadian govt. services.
- The security requirements of the organization mandate that data may not leave the confines of the organization. In this case, the procurement of physical servers and hosting on-site may be a prerequisite. My comments about cooling, power supply, dust management, and physical security should be borne in mind then.
- Cloud server costs can get away from you if not carefully managed. Some cloud vendors are, in my opinion, better suited for their ability to scale and bring online/offline computing resources than they are for hosting long-running servers. Amazon was an example of this last time I looked into it. Hetzner gives pretty good value, even for long-running servers.
- Cloud servers may experience contention issues. In a project we have with a US-based client we were finding database performance very slow. It turned out that a lot of other servers using the same shared physical storage were adversely affecting disk performance.
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/.
Data defined settings for grid placements in QGIS 3.12
For a while now I have been trying to simulate the 1in50k topographic maps of South Africa. I started using QGIS since version 1.8 and I couldn't replicate the cartography on the topographic maps but over time as QGIS has matured, I could replicate the NGI maps. NGI uses proprietary software and then Adobe to fine-tune some context on the maps. For this exercise I used QGIS 3.12.0
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.
Batch count vector features intersecting series of blocks in PostgreSQL
The national mapping agency in South Africa (NGI ) caters for national mapping, digital topographic and other Geo-Spatial Information services. The department is mandated to provide spatial data for the whole country. In most cases, they have an in-house team that is responsible for digitizing aerial photography, field validation to produce vector data that is used to make 1:50 000 topographic maps.
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):
FBIS 2 Launch Workshop
Mounting a storage drive in Hetzner cloud for rancher deployments
This article builds upon an earlier blog post by Tim Sutton on using-a-sambacifs-mount-as-a-docker-volume. In the previous article, Tim described the process of mounting a storage driver in detail.
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:
Year in Review: 2018
It’s been another awesome year for our Team. We have come a long way since establishing Kartoza in 2014, building many different software products, making friends and working with existing and new clients. Forming a company around an open source friendly business model presents many challenges but is also extremely rewarding. Here is our 2018 year end review that we would like to share with you!
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.