title: Multiple frequency range imaging to remove measurement ambiguity

authors: Payne, Andrew D.

subjects: range imaging system

abstract: Range imaging systems use a specialised sensor to capture an image where object distance (range) is measured for every pixel using time-of-flight. The scene is illuminated with an amplitude modulated light source, and the phase of the modulation envelope of the reflected light is measured to determine flight time, hence object distance for each pixel. As the modulation waveform is cyclic, an ambiguity problem exists if the phase shift exceeds 2π radians. To overcome this problem we demonstrate a method that superposes two different modulation frequencies within a single capture. This technique reduces the associated overhead compared with performing two sequential measurements, allowing the system to retain high range measurement precision at rapid acquisition rates. A method is also provided to avoid interference from aliased harmonics during sampling, which otherwise contaminate the resulting range measurement. Experimental results show the potential of the multiple frequency approach; producing high measurement precision while avoiding ambiguity. The results also demonstrate the limitation of this technique, where large errors can be introduced through a combination of a low signal to noise ratio and suboptimal selection of system parameters.

text: Multiple frequency range imaging to remove measurement ambiguity Range imaging systems use a specialised sensor to capture an image where object distance (range) is measured for every pixel using time-of-flight. The scene is illuminated with an amplitude modulated light source, and the phase of the modulation envelope of the reflected light is measured to determine flight time, hence object distance for each pixel. As the modulation waveform is cyclic, an ambiguity problem exists if the phase shift exceeds 2π radians. To overcome this problem we demonstrate a method that superposes two different modulation frequencies within a single capture. This technique reduces the associated overhead compared with performing two sequential measurements, allowing the system to retain high range measurement precision at rapid acquisition rates. A method is also provided to avoid interference from aliased harmonics during sampling, which otherwise contaminate the resulting range measurement. Experimental results show the potential of the multiple frequency approach; producing high measurement precision while avoiding ambiguity. The results also demonstrate the limitation of this technique, where large errors can be introduced through a combination of a low signal to noise ratio and suboptimal selection of system parameters.

year: 2009

title: Empire in waves: A political history of surfing by Scott Laderman [Book review]

authors: Hokowhitu, Brendan

abstract: This article reviews the book “Empire in waves: A political history of surfing by Scott Laderman”, by Scott Laderman.

text: Empire in waves: A political history of surfing by Scott Laderman [Book review] This article reviews the book “Empire in waves: A political history of surfing by Scott Laderman”, by Scott Laderman.

year: 2016

title: Supervising research in Māori cultural contexts: a decolonizing, relational response

authors: Berryman, Mere

abstract: We have collaborated for 25 years as indigenous Māori and non- Māori researchers undertaking research with Māori families, their schools and communities. We have endeavored to meet our responsibilities to the Māori people (indigenous inhabitants of New Zealand) and communities with whom we have researched, as well as meet the requirements and responsibilities of our academic institutions. In this paper, we reflect on the implications of these responsibilities for our work as supervisors of master’s and doctoral students (Māori and non-Māori) who seek to draw on decolonizing methodologies as they undertake research in Māori cultural contexts. We draw on the experiences and interactions we have had with four different postgraduate students whose research on improving educational outcomes for Māori students has required them to engage and participate in Māori cultural contexts.

text: Supervising research in Māori cultural contexts: a decolonizing, relational response We have collaborated for 25 years as indigenous Māori and non- Māori researchers undertaking research with Māori families, their schools and communities. We have endeavored to meet our responsibilities to the Māori people (indigenous inhabitants of New Zealand) and communities with whom we have researched, as well as meet the requirements and responsibilities of our academic institutions. In this paper, we reflect on the implications of these responsibilities for our work as supervisors of master’s and doctoral students (Māori and non-Māori) who seek to draw on decolonizing methodologies as they undertake research in Māori cultural contexts. We draw on the experiences and interactions we have had with four different postgraduate students whose research on improving educational outcomes for Māori students has required them to engage and participate in Māori cultural contexts.

year: 2017