title: Estimating heading direction from monocular video sequences using biologically-based sensor

authors: Cree, Michael J.

subjects: Cameras

abstract: The determination of one’s movement through the environment (visual odometry or self-motion estimation) from monocular sources such as video is an important research problem because of its relevance to robotics and autonomous vehicles. The traditional computer vision approach to this problem tracks visual features across frames in order to obtain 2-D image motion estimates from which the camera motion can be derived. We present an alternative scheme which uses the properties of motion sensitive cells in the primate brain to derive the image motion and the camera heading vector. We tested heading estimation using a camera mounted on a linear translation table with the line of sight of the camera set at a range of angles relative to straight ahead (0◦ to 50◦ in 10◦ steps). The camera velocity was also varied (0.2, 0.4, 0.8, 1.2, 1.6 and 2.0 m/s). Our biologically-based method produced accurate heading estimates over a wide range of test angles and camera speeds. Our approach has the advantage of being a one-shot estimator and not requiring iterative search techniques for finding the heading.

text: Estimating heading direction from monocular video sequences using biologically-based sensor The determination of one’s movement through the environment (visual odometry or self-motion estimation) from monocular sources such as video is an important research problem because of its relevance to robotics and autonomous vehicles. The traditional computer vision approach to this problem tracks visual features across frames in order to obtain 2-D image motion estimates from which the camera motion can be derived. We present an alternative scheme which uses the properties of motion sensitive cells in the primate brain to derive the image motion and the camera heading vector. We tested heading estimation using a camera mounted on a linear translation table with the line of sight of the camera set at a range of angles relative to straight ahead (0◦ to 50◦ in 10◦ steps). The camera velocity was also varied (0.2, 0.4, 0.8, 1.2, 1.6 and 2.0 m/s). Our biologically-based method produced accurate heading estimates over a wide range of test angles and camera speeds. Our approach has the advantage of being a one-shot estimator and not requiring iterative search techniques for finding the heading.

year: 2016

title: Eruption and emplacement of the 1.3-Ma Ongatiti Ignimbrite, New Zealand:  Regional pathways, particle processes, and pumice evolution associated with a large-volume pyroclastic flow deposit

authors: Yousef Zadeh, Elham

abstract: Pyroclastic flows are the most devastating phenomena of explosive volcanic eruptions. These hazardous density currents are able to travel several tens of kilometers radially away from their source as fast, hot density currents. Due to the enveloping ash cloud, it is still impossible to directly study pyroclastic flows, however, their deposits (i.e. ignimbrites) provide useful insight into their internal processes.

The Ongatiti Ignimbrite was sourced from Mangakino caldera (1600-950 ka), the oldest volcanic center in the Taupo Volcanic Zone, North Island, New Zealand. The crystal- and pumice-rich ignimbrite offers a unique opportunity to understand an ancient and large-volume pyroclastic flow as well as more details about particle processes and pumice evolution. The minimum deposit volume for the Ongatiti Ignimbrite has been revised to approximately 720 km³, or 512 km³ dense rock equivalent. Previous studies proposed ages from 1.21 to 1.28 Ma by dating methods, such as ⁴⁰Ar/³⁹Ar, K/Ar, and zircon fission-track. This research used the (U-Th)/He method to determine an age of 1.3 Ma. 

This study has combined field facies analysis and GIS methods to characterize the Ongatiti Ignimbrite. The topographic controls on the spatial distribution of the ignimbrite has been determined to understand pyroclastic flow pathways through valleys and over hills. The Ongatiti Ignimbrite was a landscape-modifying event that covered at least the western North Island and as far away as Auckland and Wellington. It is a welded to non-welded, columnar-jointed, cliff-forming deposit, that has been divided into nine facies based on the variation in pumice and lithic clast abundance, and welding rank. 
This study also focuses on the texture and components of the ignimbrite matrix to better understand the magma fragmentation process, the transportational and depositional dynamics of the gas-ash fluid, and the post-emplacement processes. The microtextures of ignimbrite matrix were described and quantified by using optical microscopy, scanning electron microscopy, synchrotron x-ray microtomography, electron probe microanalysis, and X-ray powder diffraction (XRD).
The matrix is poorly sorted and varies in the size and texture of ash-sized pumice fragments, glass shards, crystals, and lithic clasts. Glass shards range in shape between dominantly platy, Y-shaped, and complex shapes, and in size from a few microns to about 900 microns. The matrix is crystal-rich and comprises primary subhedral to anhedral volcanic crystals (plagioclase, quartz, pyroxene, hornblende, and Ti-Fe oxides and range between 100 to a few 1000 microns in size. The degree of welding in the matrix is defined by crystal-crystal contacts and deformation of glass shards around particles, and the highest degree of welding is shown by moderately deformed shards. 
The physical characteristics and chemical composition of pumice clasts were determined, and the main pumice textures were recognised as vesicular, fibrous, microvesicular and dense type.  Tomographic imaging shows different vesicularities and local crystal arrangement within pumice and ignimbrite. Glass chemical analysis shows two different groups, higher-silica (~80-81 wt%), and high-silica (76-78 wt%). 
The Ongatiti Ignimbrite was emplaced by a super-eruption with a volcanic explosivity index (VEI) of 7, and eruptions of similar size could catastrophically bury a vast area of the North Island. The matrix of the Ongatiti Ignimbrite suggests complex particle interactions within the ash-gas fluid of pyroclastic flows. Microtomographic imaging of ignimbrite components offers new insights into understanding these complex processes.

text: Eruption and emplacement of the 1.3-Ma Ongatiti Ignimbrite, New Zealand:  Regional pathways, particle processes, and pumice evolution associated with a large-volume pyroclastic flow deposit Pyroclastic flows are the most devastating phenomena of explosive volcanic eruptions. These hazardous density currents are able to travel several tens of kilometers radially away from their source as fast, hot density currents. Due to the enveloping ash cloud, it is still impossible to directly study pyroclastic flows, however, their deposits (i.e. ignimbrites) provide useful insight into their internal processes.

The Ongatiti Ignimbrite was sourced from Mangakino caldera (1600-950 ka), the oldest volcanic center in the Taupo Volcanic Zone, North Island, New Zealand. The crystal- and pumice-rich ignimbrite offers a unique opportunity to understand an ancient and large-volume pyroclastic flow as well as more details about particle processes and pumice evolution. The minimum deposit volume for the Ongatiti Ignimbrite has been revised to approximately 720 km³, or 512 km³ dense rock equivalent. Previous studies proposed ages from 1.21 to 1.28 Ma by dating methods, such as ⁴⁰Ar/³⁹Ar, K/Ar, and zircon fission-track. This research used the (U-Th)/He method to determine an age of 1.3 Ma. 

This study has combined field facies analysis and GIS methods to characterize the Ongatiti Ignimbrite. The topographic controls on the spatial distribution of the ignimbrite has been determined to understand pyroclastic flow pathways through valleys and over hills. The Ongatiti Ignimbrite was a landscape-modifying event that covered at least the western North Island and as far away as Auckland and Wellington. It is a welded to non-welded, columnar-jointed, cliff-forming deposit, that has been divided into nine facies based on the variation in pumice and lithic clast abundance, and welding rank. 
This study also focuses on the texture and components of the ignimbrite matrix to better understand the magma fragmentation process, the transportational and depositional dynamics of the gas-ash fluid, and the post-emplacement processes. The microtextures of ignimbrite matrix were described and quantified by using optical microscopy, scanning electron microscopy, synchrotron x-ray microtomography, electron probe microanalysis, and X-ray powder diffraction (XRD).
The matrix is poorly sorted and varies in the size and texture of ash-sized pumice fragments, glass shards, crystals, and lithic clasts. Glass shards range in shape between dominantly platy, Y-shaped, and complex shapes, and in size from a few microns to about 900 microns. The matrix is crystal-rich and comprises primary subhedral to anhedral volcanic crystals (plagioclase, quartz, pyroxene, hornblende, and Ti-Fe oxides and range between 100 to a few 1000 microns in size. The degree of welding in the matrix is defined by crystal-crystal contacts and deformation of glass shards around particles, and the highest degree of welding is shown by moderately deformed shards. 
The physical characteristics and chemical composition of pumice clasts were determined, and the main pumice textures were recognised as vesicular, fibrous, microvesicular and dense type.  Tomographic imaging shows different vesicularities and local crystal arrangement within pumice and ignimbrite. Glass chemical analysis shows two different groups, higher-silica (~80-81 wt%), and high-silica (76-78 wt%). 
The Ongatiti Ignimbrite was emplaced by a super-eruption with a volcanic explosivity index (VEI) of 7, and eruptions of similar size could catastrophically bury a vast area of the North Island. The matrix of the Ongatiti Ignimbrite suggests complex particle interactions within the ash-gas fluid of pyroclastic flows. Microtomographic imaging of ignimbrite components offers new insights into understanding these complex processes.

year: 2020

title: Iwi sex ratios in the New Zealand population census: Why are women so dominant?

authors: Kukutai, Tahu

abstract: Recent census-based studies of iwi (tribal) population growth have revealed a high degree of volatility that cannot be explained by demographic factors alone. Although focused on a small number of iwi, these studies have shown that changing patterns of identification are an important driver of iwi population growth, and that the propensity to identify with an iwi appears to be much stronger among Māori women than men. Thus, the vast majority of iwi in the census have far more females than males, and female domination has increased over time. This paper describes the key features of female-favoured iwi sex ratios in the census and explores possible explanations. Focusing on sex ratios for the ten largest iwi, we find that female domination is highest in the 25–44 age group, and that this pattern is consistent over time. Further analysis shows that Māori women aged 25–34 years are more likely than their male counterparts to know detailed aspects of their pepeha (tribal identity), to explore whakapapa (genealogy) and to speak te reo Māori. Our results underscore the importance of Māori women as cultural connectors within their whānau, as well as in a broader iwi context.

text: Iwi sex ratios in the New Zealand population census: Why are women so dominant? Recent census-based studies of iwi (tribal) population growth have revealed a high degree of volatility that cannot be explained by demographic factors alone. Although focused on a small number of iwi, these studies have shown that changing patterns of identification are an important driver of iwi population growth, and that the propensity to identify with an iwi appears to be much stronger among Māori women than men. Thus, the vast majority of iwi in the census have far more females than males, and female domination has increased over time. This paper describes the key features of female-favoured iwi sex ratios in the census and explores possible explanations. Focusing on sex ratios for the ten largest iwi, we find that female domination is highest in the 25–44 age group, and that this pattern is consistent over time. Further analysis shows that Māori women aged 25–34 years are more likely than their male counterparts to know detailed aspects of their pepeha (tribal identity), to explore whakapapa (genealogy) and to speak te reo Māori. Our results underscore the importance of Māori women as cultural connectors within their whānau, as well as in a broader iwi context.

year: 2017