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Just some thoughts, experiences and digital post-it notes about GIS, and cool stuff I get to do. Mostly Open Source GIS, Python and JS. The posts here are written by Dror Bogin and are not to be used commercially without explicit, and case specific written authorization.

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Showing posts with the label QGIS Custom Expression Functions

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Exploring The QGIS Expression Engine, Part 3: Writing Custom Expression Functions

on May 01, 2024

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Using Map Themes in QGIS

Map themes can seem daunting at first, but once you get used to them, combining them with expressions ( and variables ) can make your workflow a lot faster and make your work easier. So what are map themes? how can you use them easily? and why should you? What Are Map Themes? Let's say you want to make multiple maps, each showing the same layers, but with different symbology or with another layer added to each of them. Map themes are made specifically for that, it's basically saving your place in a way, the project remembers which layers are turned on, and that's it. The current symbology of the layers isn't saved, so watch that when you change it, the theme will remain the same theme. For example, if we have 3 layers: the OpenStreetMap basemap, a landuse layer, and a buildings layer we can set that as a map theme. Adding another layer or switching the basemap off and turning a satellite basemap on can be a second theme, there's a good example exactly like that in L...

Open Source Workflows: Keeping QGIS2Web Maps Up To Date

This post is a sort of fusion between two former posts that I realized can do something pretty useful together, I am going to take the simple storage of point data in Google Sheets that you might have read about in Collaborative Mapping With Leaflet And Google Sheets and the simple editing of your web map styles in Maputnik that I displayed in Open Source Workflows: QGIS2Web and 3D Extrusion Maps where we edited the output of QGIS2Web to create a 3D interactive map. The idea here is you can store your data in Google Sheets (whether you want to have another app update it is up to you) and have an updated version as soon as a user opens or refreshes your site. TL;DR workflow: 1. Create Google Sheet with data that you DO need to update. 2. Add Google Apps Script simple API to get your updated data in GeoJSON format. 3. Create simple map with the data that you DON'T need to update and a link to your Google Sheets "Layer" in QGIS and export it with QGIS2...

Open Source Workflows: QGIS2Web and 3D Extrusion Maps

If you use QGIS2Web you might have noticed it lacks the ability to produce 3D extruded layers, even though that symbology type is supported in MapBox GL JS (and MapLibre GL JS). We can get around that with a rather simple workflow involving using Maputnik with its ability to create and edit MapBox styles. In order to explain this, I'll first get some OSM data to display in 3D (i.e. buildings, this method is for extruding polygons), if you want to use your own data, all you have to know is that it needs to have the base height (where does the polygon start, in meters above ground, can be 0) in a field and the extrusion height in another field, this should be the total height of the extrusion, i.e. the height in meters of the top of the extruded polygon. If this sounds confusing, I recommend checking out MapBox's example of indoor mapping with their library, in the example we have one layer of extruded polygons with 3 types: 1. the floor, which h...

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