title: Adapting the bidirectional Kalman filter for use in multi-frequency Time-of-flight range imaging

authors: Alqassab, Ali

subjects: Time-of-flight

abstract: Time-of-flight range imaging cameras obtain range by producing amplitude modulated light and measuring the time taken for light to travel to the scene and back to the camera. Time-of-flight cameras require at least three raw measurements to calculate range. Raw frames are captured sequentially, and as such, motion in scenes during capture leads to inconsistent raw frame measurements and erroneous range calculations. Motion error constrains Time-of-flight cameras to non-dynamic scenes and limits their potential applications. The Time-of-flight bidirectional Kalman filter method is a state-of-the-art method known to reduce error due to transverse motion in cameras operating with a single modulation frequency. The method works by treating raw frames as a noisy time series and running the Kalman filter on it to produce a range estimation at every raw frame. The Kalman filter is then reapplied to the data in reverse to produce another set of range estimations, and a composite range is selected from the two set of range estimations. A number of commercial timeof-flight cameras, such as the Microsoft Kinect V2, use multiple modulation frequencies. In this thesis, we adapt the bidirectional Kalman filter method to multi-frequency operated cameras by having the prediction component of the Kalman filter take into account the change in amplitude and phase shift caused by the change in frequency. The amplitude component of the prediction is performed linearly by multiplication, while the phase shift component of the prediction is performed using the ratio of the modulation frequencies. The phase shift prediction across modulation frequencies requires the phase to be unwrapped. The unwrapping is performed between modulation frequencies by selecting the number of phase wraps that best predicts the two following raw frames. Finally, to ensure correct composite phase selection, an alternative method for selecting the composite phase is proposed for the adapted bidirectional Kalman filter. We perform quantitative and qualitative experiments to test the proposed method. In the quantitative experiment, the proposed method produces less error than the classical Discrete Fourier Transform approach in 70% of tested instances. The qualitative experiment shows that the proposed method significantly reduces motion blur.

text: Adapting the bidirectional Kalman filter for use in multi-frequency Time-of-flight range imaging Time-of-flight range imaging cameras obtain range by producing amplitude modulated light and measuring the time taken for light to travel to the scene and back to the camera. Time-of-flight cameras require at least three raw measurements to calculate range. Raw frames are captured sequentially, and as such, motion in scenes during capture leads to inconsistent raw frame measurements and erroneous range calculations. Motion error constrains Time-of-flight cameras to non-dynamic scenes and limits their potential applications. The Time-of-flight bidirectional Kalman filter method is a state-of-the-art method known to reduce error due to transverse motion in cameras operating with a single modulation frequency. The method works by treating raw frames as a noisy time series and running the Kalman filter on it to produce a range estimation at every raw frame. The Kalman filter is then reapplied to the data in reverse to produce another set of range estimations, and a composite range is selected from the two set of range estimations. A number of commercial timeof-flight cameras, such as the Microsoft Kinect V2, use multiple modulation frequencies. In this thesis, we adapt the bidirectional Kalman filter method to multi-frequency operated cameras by having the prediction component of the Kalman filter take into account the change in amplitude and phase shift caused by the change in frequency. The amplitude component of the prediction is performed linearly by multiplication, while the phase shift component of the prediction is performed using the ratio of the modulation frequencies. The phase shift prediction across modulation frequencies requires the phase to be unwrapped. The unwrapping is performed between modulation frequencies by selecting the number of phase wraps that best predicts the two following raw frames. Finally, to ensure correct composite phase selection, an alternative method for selecting the composite phase is proposed for the adapted bidirectional Kalman filter. We perform quantitative and qualitative experiments to test the proposed method. In the quantitative experiment, the proposed method produces less error than the classical Discrete Fourier Transform approach in 70% of tested instances. The qualitative experiment shows that the proposed method significantly reduces motion blur.

year: 2020

title: Impacts of Early Childhood Education Social Obligations on Families and Whanau

authors: Randall, Judith

subjects: early childhood education

abstract: This thesis explores the impacts of ECE social obligations on affected families and whānau. In 2013 ECE social obligations were introduced through the Social Security (Benefit Categories and Work Focus) Amendment Bill. These obligations require beneficiaries to ensure their children are “enrolled in and attending an approved early childhood education programme from the age of three, until they start school” (Work and Income New Zealand, 2013c). 
A qualitative approach was utilised to hear the voices of those affected. Data was gathered through interviews with eight beneficiary families and two ECE centre managers who had knowledge of the impacts of obligations.  Perceived impacts were analysed using thematic analysis. An examination of the discourses underpinning these obligations as represented in policy documents was undertaken utilising Bacchi’s (2000; 1999) “what’s the problem?” framework.
The introduction of the ECE social obligation policy was found to have placed responsibility on beneficiaries but to have failed to adequately address barriers to ECE participation that families face. The study identified many barriers which impede a family’s ability to participate in ECE. These include transportation, cost, and provision of high quality, suitable ECE for their children available in their local community. Mandatory ECE does not provide the infrastructure needed to enable families to access ECE programmes as it does not address the accessibility, structural, and personal barriers that families face. The thesis argues that the context of incorporating ECE policy in Ministry of Social Development (MSD) legislation and the use of sanctions to ensure compliance is likely to lead to negative outcomes for children’s well-being. 
Policy-as-discourse analysis identified that social obligations were conceived in the context of reducing long-term benefit dependency. The three interrelated dominant discourses underpinning this policy, economic rationalisation, the positioning of beneficiaries as job seekers, and the positioning of children as vulnerable, has left the child as citizen invisible. I advocate that redefining the problem through a child as citizen lens could provide a framework for government to support families through barriers and address provision of high quality ECE. 
Three key suggestions are made. Firstly, utilisation of a child’s rights framework could ensure children’s rights are at the forefront of ECE policy.  This would enable the primary emphasis to be on the welfare and best interests of all children. Within this framework this study identified the need for ECE matters to be in the jurisdiction of the Ministry of Education, rather than MSD, in order to ensure consistency and accessibility to quality ECE for all children. Secondly, ECE engagement needs to be promoted through a positive model rather than sanctions. Government financial investment in integrated ECE services within local communities could aid families to overcome participation barriers and provide an ideal model for enabling families to access social services.  Thirdly, government policy and funding needs to support provision of high quality ECE services that are responsive to their local communities. Such services are essential to encouraging ECE participation.

text: Impacts of Early Childhood Education Social Obligations on Families and Whanau This thesis explores the impacts of ECE social obligations on affected families and whānau. In 2013 ECE social obligations were introduced through the Social Security (Benefit Categories and Work Focus) Amendment Bill. These obligations require beneficiaries to ensure their children are “enrolled in and attending an approved early childhood education programme from the age of three, until they start school” (Work and Income New Zealand, 2013c). 
A qualitative approach was utilised to hear the voices of those affected. Data was gathered through interviews with eight beneficiary families and two ECE centre managers who had knowledge of the impacts of obligations.  Perceived impacts were analysed using thematic analysis. An examination of the discourses underpinning these obligations as represented in policy documents was undertaken utilising Bacchi’s (2000; 1999) “what’s the problem?” framework.
The introduction of the ECE social obligation policy was found to have placed responsibility on beneficiaries but to have failed to adequately address barriers to ECE participation that families face. The study identified many barriers which impede a family’s ability to participate in ECE. These include transportation, cost, and provision of high quality, suitable ECE for their children available in their local community. Mandatory ECE does not provide the infrastructure needed to enable families to access ECE programmes as it does not address the accessibility, structural, and personal barriers that families face. The thesis argues that the context of incorporating ECE policy in Ministry of Social Development (MSD) legislation and the use of sanctions to ensure compliance is likely to lead to negative outcomes for children’s well-being. 
Policy-as-discourse analysis identified that social obligations were conceived in the context of reducing long-term benefit dependency. The three interrelated dominant discourses underpinning this policy, economic rationalisation, the positioning of beneficiaries as job seekers, and the positioning of children as vulnerable, has left the child as citizen invisible. I advocate that redefining the problem through a child as citizen lens could provide a framework for government to support families through barriers and address provision of high quality ECE. 
Three key suggestions are made. Firstly, utilisation of a child’s rights framework could ensure children’s rights are at the forefront of ECE policy.  This would enable the primary emphasis to be on the welfare and best interests of all children. Within this framework this study identified the need for ECE matters to be in the jurisdiction of the Ministry of Education, rather than MSD, in order to ensure consistency and accessibility to quality ECE for all children. Secondly, ECE engagement needs to be promoted through a positive model rather than sanctions. Government financial investment in integrated ECE services within local communities could aid families to overcome participation barriers and provide an ideal model for enabling families to access social services.  Thirdly, government policy and funding needs to support provision of high quality ECE services that are responsive to their local communities. Such services are essential to encouraging ECE participation.

year: 2014

title: A cohort history of mortality in New Zealand

authors: Pool, Ian

abstract: This paper uses the generational life tables to track historical mortality experience for New Zealand Pakeha and Māori. The key research questions we seek to explore concern with why was Pakeha life expectation so high so early, and why did this survival advantage disappeared by the mid 20th century and what has happened since? For the Māori population what was the impact of contact on Māori mortality, what were the changes that have occurred and why, and what has happened to Māori mortality recently? A key finding from the cohort mortality analysis is that gains in survivorship have momentum effects that propel this advantage forward as survivors move up through the age-groups. That said, however, periods of gain may be followed later by cohort deterioration occurring among the same generations later in their life cycle, and even by further cycles of reprise and deterioration. These cycles of gain, deterioration, reprise etc are more evident for males, and particularly for Māori. Policy implications of these findings are discussed.

text: A cohort history of mortality in New Zealand This paper uses the generational life tables to track historical mortality experience for New Zealand Pakeha and Māori. The key research questions we seek to explore concern with why was Pakeha life expectation so high so early, and why did this survival advantage disappeared by the mid 20th century and what has happened since? For the Māori population what was the impact of contact on Māori mortality, what were the changes that have occurred and why, and what has happened to Māori mortality recently? A key finding from the cohort mortality analysis is that gains in survivorship have momentum effects that propel this advantage forward as survivors move up through the age-groups. That said, however, periods of gain may be followed later by cohort deterioration occurring among the same generations later in their life cycle, and even by further cycles of reprise and deterioration. These cycles of gain, deterioration, reprise etc are more evident for males, and particularly for Māori. Policy implications of these findings are discussed.

year: 2003