Showing posts from 2016

Visibility analysis, release 0.5.4: modelling the horizon

Visibility analysis plugin for QGIS is prospering quite well. As of writing, it counts some 20 000 downloads and a bunch of « votes », which means that at least several thousand people are using it. (Although, it does feel uncomfortable knowing that any potential error would risk a blame-storm ….)

The new release brings a more polished algorithm and two options for horizon analysis. Horizon detection was, and still remains, rather problematic. On the conceptual level, the skyline has to be understood in terms of perception and not as a fixed terrain parameter. Consider the image below: there are many skylines in the mountainous landscape, progressively dissolving into the atmosphere. The most distant skyline might not even be visible at all, even if it would be rendered as “true horizon” by GIS. Sometimes we may be able to see a chain of mountains at distances above 100 or 200 km, but such views demand exceptional weather conditions. A book was recently published by Will…

Pebbles, faces and landscapes: the archaeology of simulacra

Several weeks ago I stumbled upon an amusing article on a museum displaying pebbles and rocks resembling human faces, situated in Chichibu, Japan. The stones are called jinmenseki (珍石) and one should be able to recognise human faces in their naturally occurring dents and holes. The founder of the museum, Shozo Hayama, spent some 50 years collecting these specimens, the only criterion being that human hand did not interfere with the work of nature. There are some 1700 rocks on display, carefully arranged in museum vitrines and sometimes labelled with suggestive interpretations: Elvis Presley, Gorbachev or Donkey Kong. More on the museum can be found in articles listed below.

The word on Chichubu pebble museum spread over the internet through oddities columns, together with museums of torture, toilets, bad art, broken relationships etc. I find that the pebble museum (or Chinsekikan in Japanese, which means “the hall of curious rocks”) open some curious questions for landsc…

To see or to be seen concepts, analysis and modelling of viewsheds in archaeology

Vendredi 18 novembre 2016

De 10h à 13h et de 14h à 17h -107M salle de conférence de l’UMR Chrono-environnement, UFR ST, la Bouloie, 16 route de Gray, 25030 Besançon

Séminaire Thématique organisé par Laure NUNINGER, CR CNRS et Zoran CUCKOVIC, Doctorant à l’Université de Bourgogne Franche-Comté au laboratoire de Chrono-Environnement, en collaboration avec la plateforme GeoBFC (MSHE C.N. Ledoux) et le réseau ISA (Information Spatiale et Archéologie)
______________________________________________________Voir et être vu dans un territoire : concepts, analyses et modélisation de la visibilité en archéologieTo see or to be seen over space: Concepts, analysis and modelling of viewsheds in archaeology______________________________________________________Programme : la matinée sera consacrée aux concepts, méthodes et techniques de l’analyse de visibilité appliquée en archéologie tandis que l’après-midi sera consacré à la présentation de cas d’étude protohistorique, médiéval et moderne à …

QGIS visibility analysis algorithm

It took me long time to develop an algorithm for the visibility analysis which would be comparable in terms of speed and quality to those available in other packages. And then some more time to tweak it for the type of analysis the QGIS visibility plugin is intended: higher volume calculation of multiple viewsheds over standard (coarse) elevation models. But here it is - an implementation which is faster than previous ones by a factor of 10 (at least).
1. Performance test There is a set of data files in plugin’s repository for testing purposes: a shapefile with several hundred observer points (462 to be precise) and an elevation model extracted from SRTM DEM, with 90 metres resolution (see resources below). All analyses were made using following parameters: a radius of 5000 metres for each point and eye level of 1.6 metres above ground. For ArcGis the standard viewshed module with multiple points was used (ref. below), and for QGIS plugin the cumulative visibility option…

QGIS viewshed plugin: a tutorial

I’ve had a remark recently that some kind of tutorial would be welcome for the visibility plugin. So here it goes…

The data which will be used can be downloaded from the plugin’s GitHub repo (link below). It comprises a DEM extracted from publicly available SRTM data (90 m resolution) and two sets of points (let’s call them A and B) which mostly correspond to archaeological sites I’m working on. The area in question is Istria (Croatia and Slovenia) and the projection is MGI Balkans 5 (EPSG : 31275).

A most basic use for the visibility analysis would be exploratory: would someone be able to see point B from point A? Such a query can be made by any viewshed algorithm available - but what about many observers from a number of points? In fact, when studying ancient landscapes we are often interested not only of what people could see, but also whether visibility influenced their preference for particular locations. For instance, is visibility a factor in the choice of settlement…

Advanced viewshed analysis: a Quantum GIS plug-in for the analysis of visual landscapes.

Published in: The Journal of Open Source Software 4(1). doi: 10.21105/joss.00032

Author : Zoran Čučković

Summary: Viewshed analysis is a standard feature of GIS software packages, such as ArcGIS (ESRI 2016), GRASS (Neteler et al. 2012) or ERDAS (2015). However, these implementations vary considerably in terms of their versatility and robustness. Software in the free domain is particularly poor in this respect: visibility analysis is generally implemented as a simple binary query (true/false) for elevation datasets (eg. GRASS or SAGA GIS). In order to meet the demands of a typical analysis concerning visual landscapes we would be interested to find out how deep are certain locations below the visible horizon, what is the overall visual potential of a landscape or which sites are connected in visual networks (cf. Higuchi (1983); Llobera (2003); Čučković (2015)).

Advanced viewshed analysis plug-in for open source Quantum GIS software has been made in order to meet some of these demands: b…

Fortifying seascapes: Bronze Age fortified sites of the north-eastern Adriatic Sea

(Presented at “Socio-Environmental Dynamics over the Last 12,000 Years: The Creation of Landscapes IV” conference held at Kiel University, March 24 - 27, 2015)

The north-eastern Adriatic archipelago (Kvarner, Croatia) was famously labelled as the “Amber Islands” by ancient Greek sources, testifying to its crucial position on the so-called Amber Route during the later prehistory. An intense network of maritime connections had been put in place already by the Early Neolithic, and developed particularly during the Bronze and Iron Ages under the influence of Aegean contacts.

However, the organisation of this network on local scale remains unclear, as well as the real importance of seafaring for local cultures which developed as intermediaries along the Adriatic coast. What is usually perceived as far reaching interregional maritime exchange network, most probably consisted of a series of “small worlds” characterised by different intensities of local connections, as demons…

Topohilia and the emergence of prehistoric sanctuaries (NW Balkans, 10th – 5th c. BC)

(Presented at “Rencontres doctorales archéologiques de l’EEPB Bibracte”, Centre archéologique européen du Mont Beuvray, 28 - 30 avril 2015)

In a definition given by geographer Yi Fu Tuan “ Topophilia is the affective bond between people and place or setting “. Even though this concept pertains to an intimate “sense of place” which may seem unattainable by archaeological means, it can be very useful when considering the historical dimension of the emergence of particular places, such as prehistoric ritual areas or sanctuaries.

Several major categories of ritual places can be considered: natural places used for deposition of artefacts (caves, rivers, wet areas), burial places, particular structures within settlements, and finally sanctuaries stricto sensu with enclosed space and a shrine. Each of these categories can be regarded as a particular spatial strategy, resulting in a space with high symbolic charge. Crucially, ritual places normally emerged through long term temp…