Some thoughts on hillshade models for Lidar analysis

Hillshade modelling is a standard form of terrain representation in cartography. The idea is to simulate lighting of a terrain from a certain direction (or multiple directions). The method is well known and constantly improved in GIS – as means of cartographic representation. It seems, indeed, difficult to imagine spatial analysis on shadows. However, hillshading … Continue reading Some thoughts on hillshade models for Lidar analysis

Depth below horizon: new (old) functionality for QGIS viewshed analysis

The basic idea of visibility analysis is to test whether particular locations are theoretically observable from a given observer point (« theoretically » because our data and algorithms can never ideally replicate real-world situations). Such a query yields a yes/no answer for each tested point, which is typically represented as Boolean raster in GIS software. … Continue reading Depth below horizon: new (old) functionality for QGIS viewshed analysis

Installing Python packages in QGIS 3 (for Windows)

Python is in the heart of QGIS (or in the guts if you prefer), which enables us to use tons of third party Python libraries. In Linux systems, QGIS will use the main Python installation, but in Windows things get more complicated. QGIS has it's own Python, which means we end up with various Pythons … Continue reading Installing Python packages in QGIS 3 (for Windows)

Visibility analysis for QGIS 3.0 : tackling big data

Viewshed plugin for QGIS is based on Numpy library for handling raster data. Numpy is tuned for high performance and is (relatively) easy to use. However, it relies heavily on available live memory and will break with voluminous datasets. Which is what elevation models usually are... Version 0.6.4 introduces an addition to the original algorithm … Continue reading Visibility analysis for QGIS 3.0 : tackling big data

Land visibility in the Mediterranean: a large scale model

Visibility of land was a major consideration for ancient seafaring, for reasons of navigation and security. Even if the open sea travel must have been practised already by the Neolithic period, judging by the colonisation of remote islands and by the exchange of artefacts across the Mediterranean, the sight of the land remained a much … Continue reading Land visibility in the Mediterranean: a large scale model

Lissage du modèle numérique de terrain BD ALTI

Le problème n’est pas nouveau, mais on ne trouve toujours pas de solutions simples pour le « maquillage » du modèle numérique de terrain (MNT) très couramment utilisé en France, le BD ALTI de résolution de 25 mètres (lien dessus). Celui-ci est disponible en valeurs entières, ce que lui donne un aspect en marches d’escalier … Continue reading Lissage du modèle numérique de terrain BD ALTI

Benchmarking viewshed algorithm: Nuraghi of Sardinia

The new viewshed plugin for QGIS 3 features an improved algorithm which should result in perceptible improvements in terms of efficiency. So let's give it a try! Nuraghe in Toralba-Sant'Antine © Michel Royon / Wikimedia Commons The test data I'm using are the famous nuraghi of Sardinia, drystone towers dating to the 2. millennium BC. … Continue reading Benchmarking viewshed algorithm: Nuraghi of Sardinia

Visibility analysis for QGIS 3.0

Visibility analysis plugin is now available in QGIS 3.0! It has been completely refurbished: from now on it will be integrated into the "Processing toolbox". This is a more appropriate habitat for the algorithm because of integration with the QGIS toolshed. It can be now combined with all the fancy geoprocessing tools (GRASS, SAGA etc). … Continue reading Visibility analysis for QGIS 3.0

Tanaka method or how to make shaded contour lines

Contour lines have become a commonplace, unassuming companion of our cartographic outputs - GIS has made us forget their visual potential. Already in the 19th century cartographers experimented with shaded contours, but the technique has become known as the Tanaka method, after Japanese cartographer Kitiro Tanaka (Kennelly 2016, wiki.gis 2017). Even the cover page of … Continue reading Tanaka method or how to make shaded contour lines

My first QGIS map: the aid from Cyrene

Cyrene, Lybia Sometime during the reign of Alexander of Macedon a famine broke out in Greece. We don't have many documents reporting the gravity of situation; apparently Greece was suffering much during the tumultuous years just before and after the Macedonian conquest. The prosperous city of Cyrene, on the coast of today's Libya, came to … Continue reading My first QGIS map: the aid from Cyrene