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

Le géosymbole vu par l’archéologie

Le concept du géosymbole est issu du mouvement culturaliste en géographie, suite au désenchantement, dans les années 80, par les approches structuralistes. Ces dernières donnaient l’impression de relégation de l’humain en marges du grand tableau socio-politico-économique : le discours géographique risquait de prolonger celui du pouvoir qui écrase l’individu. Ainsi, la géographie s’est à nouveau … Continue reading Le géosymbole vu par l’archéologie

Looping through numpy arrays (e.g. moving/rolling window)

Numpy is the cornerstone of matrix based calculations in QGIS (and elsewhere). It does wonders with raster data (unless it hits the limit of available live memory...). A recurrent problem with Numpy is the implementation of various looping routines, such as the sliding window which is frequently used in image filtering and other approaches focused … Continue reading Looping through numpy arrays (e.g. moving/rolling window)

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