title: Analysing and Enhancing the Coarse Registration Pipeline

authors: Larkins, Robert L.

subjects: Registration

abstract: The current and continual development of sensors and imaging systems capable of acquiring three-dimensional data provides a novel form in which the world can be expressed and examined. The acquisition process, however, is often limited by imaging systems only being able to view a portion of a scene or object from a single pose at a given time. A full representation can still be produced by shifting the system and registering subsequent acquisitions together. While many solutions to the registration problem have been proposed, there is no quintessential approach appropriate for all situations. This dissertation aims to coarsely register range images or point-clouds of a priori unknown pose by matching their overlapping regions.

Using spherical harmonics to correlate normals in a coarse registration pipeline has been shown previously to be an effective means for registering partially overlapping point-clouds. The advantage of normals is their translation invariance, which permits the rotation and translation to be decoupled and determined separately. Examining each step of this pipeline in depth allows its registration capability to be quantified and identifies aspects which can be enhanced to further improve registration performance. The pipeline consists of three primary steps: identifying the rotation using spherical harmonics, identifying the translation in the Fourier domain, and automatically verifying if alignment is correct. Having achieved coarse registration, a fine registration algorithm can be used to refine and complete the alignment.

Major contributions to knowledge are provided by this dissertation at each step of the pipeline. Point-clouds with known ground-truth are used to examine the pipeline's capability, allowing its limitations to be determined; an analysis which has not been performed previously. This examination allowed modifications to individual components to be introduced and measured, establishing their provided benefit. The rotation step received the greatest attention as it is the primary weakness of the pipeline, especially as the nature of the overlap between point-clouds is unknown. Examining three schemes for binning normals found that equiangular binning, when appropriately normalised, only had a marginal decrease in accuracy with respect to the icosahedron and the introduced Fibonacci schemes. Overall, equiangular binning was the most appropriate due to its natural affinity for fast spherical-harmonic conversion. Weighting normals was found to provide the greatest benefit to registration performance. The introduction of a straightforward method of combining two different weighting schemes using the orthogonality of complex values increased correct alignments by approximately 80% with respect to the next best scheme; additionally, point-cloud pairs with overlap as low as 5% were able to be brought into correct alignment. Transform transitivity, one of two introduced verification strategies, correctly classified almost 100% of point-cloud pair registrations when there are sufficient correct alignments.

The enhancements made to the coarse registration pipeline throughout this dissertation provide significant improvements to its performance. The result is a pipeline with state-of-the-art capabilities that allow it to register point-cloud with minimal overlap and correct for alignments that are classified as misaligned. Even with its exceptional performance, it is unlikely that this pipeline has yet reached its pinnacle, as the introduced enhancements have the potential for further development.

text: Analysing and Enhancing the Coarse Registration Pipeline The current and continual development of sensors and imaging systems capable of acquiring three-dimensional data provides a novel form in which the world can be expressed and examined. The acquisition process, however, is often limited by imaging systems only being able to view a portion of a scene or object from a single pose at a given time. A full representation can still be produced by shifting the system and registering subsequent acquisitions together. While many solutions to the registration problem have been proposed, there is no quintessential approach appropriate for all situations. This dissertation aims to coarsely register range images or point-clouds of a priori unknown pose by matching their overlapping regions.

Using spherical harmonics to correlate normals in a coarse registration pipeline has been shown previously to be an effective means for registering partially overlapping point-clouds. The advantage of normals is their translation invariance, which permits the rotation and translation to be decoupled and determined separately. Examining each step of this pipeline in depth allows its registration capability to be quantified and identifies aspects which can be enhanced to further improve registration performance. The pipeline consists of three primary steps: identifying the rotation using spherical harmonics, identifying the translation in the Fourier domain, and automatically verifying if alignment is correct. Having achieved coarse registration, a fine registration algorithm can be used to refine and complete the alignment.

Major contributions to knowledge are provided by this dissertation at each step of the pipeline. Point-clouds with known ground-truth are used to examine the pipeline's capability, allowing its limitations to be determined; an analysis which has not been performed previously. This examination allowed modifications to individual components to be introduced and measured, establishing their provided benefit. The rotation step received the greatest attention as it is the primary weakness of the pipeline, especially as the nature of the overlap between point-clouds is unknown. Examining three schemes for binning normals found that equiangular binning, when appropriately normalised, only had a marginal decrease in accuracy with respect to the icosahedron and the introduced Fibonacci schemes. Overall, equiangular binning was the most appropriate due to its natural affinity for fast spherical-harmonic conversion. Weighting normals was found to provide the greatest benefit to registration performance. The introduction of a straightforward method of combining two different weighting schemes using the orthogonality of complex values increased correct alignments by approximately 80% with respect to the next best scheme; additionally, point-cloud pairs with overlap as low as 5% were able to be brought into correct alignment. Transform transitivity, one of two introduced verification strategies, correctly classified almost 100% of point-cloud pair registrations when there are sufficient correct alignments.

The enhancements made to the coarse registration pipeline throughout this dissertation provide significant improvements to its performance. The result is a pipeline with state-of-the-art capabilities that allow it to register point-cloud with minimal overlap and correct for alignments that are classified as misaligned. Even with its exceptional performance, it is unlikely that this pipeline has yet reached its pinnacle, as the introduced enhancements have the potential for further development.

year: 2015

title: Visualising Time

authors: Clarke, Greg

subjects: Time

abstract: This study investigates the visualisation of temporal relationships between objects.  A popular method employed for such information visualisations is the time line consisting of a single horizontal axis along which temporal events or objects are depicted at specific points or intervals.  The orientation of the temporal progression along the axis line will generally coincide with the orientation of the literary writing progression of the culture and language.  For example a time line visualised in a Western culture with English as its literary base will exhibit a temporal progression orientation of early/left, later/right whereas Arabian culture with an Arabic literary base will exhibit the reverse temporal progression orientation.  In both cultures and languages temporal metaphor use spatial concepts to describe temporal relationships with no discourse to transversal orientation.  This is reflected by never hearing the phrase “the months to the right” but rather “the months ahead”.  In science, Einstein showed via his special and general theories of relativity that time and space are interlinked.  The scientific rationalisation of time and space along with the use of spatial concepts as temporal metaphor implies that the underlying perception of time is spatial.  Information visualisations are the externalisations of our perceptions.  Therefore temporal information visualisations should employ spatial visualisation techniques.
This study evaluated spatial visualisation techniques for temporal information visualisations via a web survey.  The spatial temporal information visualisations used in the survey employed no temporal cues such as time or date stamps but conferred all temporal progression via spatial cues.  The findings from the analysis of the participant responses to the survey showed that spatial cues do impart temporal cues for temporal relationships.

text: Visualising Time This study investigates the visualisation of temporal relationships between objects.  A popular method employed for such information visualisations is the time line consisting of a single horizontal axis along which temporal events or objects are depicted at specific points or intervals.  The orientation of the temporal progression along the axis line will generally coincide with the orientation of the literary writing progression of the culture and language.  For example a time line visualised in a Western culture with English as its literary base will exhibit a temporal progression orientation of early/left, later/right whereas Arabian culture with an Arabic literary base will exhibit the reverse temporal progression orientation.  In both cultures and languages temporal metaphor use spatial concepts to describe temporal relationships with no discourse to transversal orientation.  This is reflected by never hearing the phrase “the months to the right” but rather “the months ahead”.  In science, Einstein showed via his special and general theories of relativity that time and space are interlinked.  The scientific rationalisation of time and space along with the use of spatial concepts as temporal metaphor implies that the underlying perception of time is spatial.  Information visualisations are the externalisations of our perceptions.  Therefore temporal information visualisations should employ spatial visualisation techniques.
This study evaluated spatial visualisation techniques for temporal information visualisations via a web survey.  The spatial temporal information visualisations used in the survey employed no temporal cues such as time or date stamps but conferred all temporal progression via spatial cues.  The findings from the analysis of the participant responses to the survey showed that spatial cues do impart temporal cues for temporal relationships.

year: 2013

title: “On and On It Goes”: Representations of the New Zealand Wars in novels, film, and theatre

authors: Sheridan, Brendan Daniel

subjects: History

abstract: This thesis considers fictional representations of the New Zealand Wars. Through the media of novels, feature films, and drama with links to Shakespeare, it explores common features between representations. It examines how these representations change in tone or style over time and how different representations negotiate the complex issues of race, gender, and colonialism.
	I examine key representations ranging from 1861 to 2017 in terms of genre. I begin with the nineteenth-century novel as many of the key tropes used in representations of the New Zealand Wars emerge in this period. I then look at the twentieth-century novel, before concentrating specifically on Maurice Shadbolt and Witi Ihimaera. My discussion then turns to the genres of film and theatre. In all of these diverse representations there are recurring tropes and motifs. Many of the fictions feature stock characters such as the European traveller, the imperial official, and the Māori maiden and bear the imprint of historical romance conventions, popularised by Sir Walter Scott’s Waverly and James Fenimore Cooper’s The Last of the Mohicans. The vast majority of stories take place in the North Island between 1860 and 1870. Variations in the depiction of historical events are shaped by the historical scholarship and dominant ideologies of the time, such as the post-colonial tonal shift that emerges following the publication of work by James Belich and Ranginui Walker. I contextualise representations with their point in history, and how they treat the New Zealand Wars in terms of events, characters, and historical figures. 
	Through this approach, my thesis argues that representations of the New Zealand Wars do not form themselves in isolation and do not occur in isolated clusters. This thesis seeks to demonstrate that representations of the New Zealand Wars occur on a steady continuum. Representations of the conflict exist in parallel to one another (intentional or not) and are affected by the social climate, dominant ideologies, and published histories available to the author at the time of writing. The variety of representations—novel, feature film, stage play—share many core tropes. Even so, chronologically this continuum also features shifts in tone, ideologies, and sympathies. A novel of the 1980s has a very different perspective regarding settlers compared to a novel from the 1860s. In the same manner, a play staged in the 2000s shows a different attitude towards the conflict compared to a film from the 1940s. This thesis demonstrates that while representations of the New Zealand Wars share a common subject, how they approach the material is constantly evolving.

text: “On and On It Goes”: Representations of the New Zealand Wars in novels, film, and theatre This thesis considers fictional representations of the New Zealand Wars. Through the media of novels, feature films, and drama with links to Shakespeare, it explores common features between representations. It examines how these representations change in tone or style over time and how different representations negotiate the complex issues of race, gender, and colonialism.
	I examine key representations ranging from 1861 to 2017 in terms of genre. I begin with the nineteenth-century novel as many of the key tropes used in representations of the New Zealand Wars emerge in this period. I then look at the twentieth-century novel, before concentrating specifically on Maurice Shadbolt and Witi Ihimaera. My discussion then turns to the genres of film and theatre. In all of these diverse representations there are recurring tropes and motifs. Many of the fictions feature stock characters such as the European traveller, the imperial official, and the Māori maiden and bear the imprint of historical romance conventions, popularised by Sir Walter Scott’s Waverly and James Fenimore Cooper’s The Last of the Mohicans. The vast majority of stories take place in the North Island between 1860 and 1870. Variations in the depiction of historical events are shaped by the historical scholarship and dominant ideologies of the time, such as the post-colonial tonal shift that emerges following the publication of work by James Belich and Ranginui Walker. I contextualise representations with their point in history, and how they treat the New Zealand Wars in terms of events, characters, and historical figures. 
	Through this approach, my thesis argues that representations of the New Zealand Wars do not form themselves in isolation and do not occur in isolated clusters. This thesis seeks to demonstrate that representations of the New Zealand Wars occur on a steady continuum. Representations of the conflict exist in parallel to one another (intentional or not) and are affected by the social climate, dominant ideologies, and published histories available to the author at the time of writing. The variety of representations—novel, feature film, stage play—share many core tropes. Even so, chronologically this continuum also features shifts in tone, ideologies, and sympathies. A novel of the 1980s has a very different perspective regarding settlers compared to a novel from the 1860s. In the same manner, a play staged in the 2000s shows a different attitude towards the conflict compared to a film from the 1940s. This thesis demonstrates that while representations of the New Zealand Wars share a common subject, how they approach the material is constantly evolving.

year: 2019