First time I heard of something like “natural places” was some ten years ago at a conference in Slovenia. Several, mostly young researchers were proud to demonstrate an existence of non-man-made features on their sites, features that apparently gained a symbolic value before or during human habitation. For instance, trees which were incorporated in Neolithic … Continue reading Natural places and archaeology
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
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
Polar (circular) diagram
Orientation of geographic features can be an important piece of information, for instance when studying ancient field systems or analysing geological formations. The problem comes when we try to summarise such data graphically . Standard histograms are not ideal because they cut through the continuous distribution - one cannot easily understand the relationship between the … Continue reading Polar (circular) diagram
SIG collaboratif, solution simple et gratuite
Travailler, ce n’est peut-être pas toujours la chose la plus passionnante, mais c’est quand même plus amusant (et plus efficace) en collaboration. Il y a, dans le monde du SIG, bien de solutions pour le travail collaboratif sur un même jeu de données, mais le plus souvent elles sont coûteuses ou exigeantes au niveau technique. … Continue reading SIG collaboratif, solution simple et gratuite