title: Verification of multi-view point-cloud registration for spherical harmonic cross-correlation

authors: Larkins, Robert L.

subjects: 3D imaging

abstract: Spherical harmonic cross-correlation is a robust registration algorithm that brings two point-clouds of the same scene into coarse rotational alignment. The found rotation however may not give the desired alignment, as misalignments can occur if there is not enough overlap between point-clouds, or if they contain a form of symmetry. We propose a verification method whose purpose is to determine if registration has failed for a priori unknown registration. The rotational transformation between multiple clouds must satisfy internal consistency, namely multiple rotational transformations are transitive. The rotation verification is performed using triplets of images, which are cross-referenced with each other to classify rotations individually. Testing is performed on a dataset of a priori known registrations. It is found that when the number of images or the percentage of correct rotations is increased, the number of correct rotation classifications improves. Even when tested with only four images and a correct rotation percentage of 17%, the rotation verification is still considered a viable method for classifying rotations. Spherical harmonic cross-correlation is benefited by rotation verification as it provides an additional approach for checking whether found rotations are correct.

text: Verification of multi-view point-cloud registration for spherical harmonic cross-correlation Spherical harmonic cross-correlation is a robust registration algorithm that brings two point-clouds of the same scene into coarse rotational alignment. The found rotation however may not give the desired alignment, as misalignments can occur if there is not enough overlap between point-clouds, or if they contain a form of symmetry. We propose a verification method whose purpose is to determine if registration has failed for a priori unknown registration. The rotational transformation between multiple clouds must satisfy internal consistency, namely multiple rotational transformations are transitive. The rotation verification is performed using triplets of images, which are cross-referenced with each other to classify rotations individually. Testing is performed on a dataset of a priori known registrations. It is found that when the number of images or the percentage of correct rotations is increased, the number of correct rotation classifications improves. Even when tested with only four images and a correct rotation percentage of 17%, the rotation verification is still considered a viable method for classifying rotations. Spherical harmonic cross-correlation is benefited by rotation verification as it provides an additional approach for checking whether found rotations are correct.

year: 2012

title: Evaluating the potential of historic sheep dips as point sources of trace element and organochlorine pollutants

authors: Tulagi, Asaeli

subjects: Sheep dip

abstract: Sheep dipping was a historic agricultural practice where sheep were immersed into insecticides to eradicate external parasites. Historical use of pesticides has caused localised soil contamination at former sheep dipping sites. There is limited information on offsite contamination such as in stream sediments, groundwater, and surface water. Predominant contaminants at historic sheep dipping sites are arsenic (As) and organochlorine (OC) compounds. There are estimated to be 50,000 former sheep dip sites in New Zealand, of which, over 10,000 are estimated to be in the Waikato Region.  Contamination at historical sheep dip sites is potentially concerning for human and environmental health.

The objectives of this study were to (1) evaluate a range of historic sheep dips to identify sites that had the highest leaching potential; (2) characterise the selected study sites; (3) establish the extent of contamination in soil, sediments, and water; (4) evaluate the extent of offsite contamination; and (5) assess compliance to environmental guideline limits.

Soil samples from two former sheep dip sites were analysed for arsenic, copper, and organochlorines at depths of up to 20 cm. Further soil samples were analysed for arsenic at depths of up to 7.5 cm. Stream water and sediment samples were analysed for arsenic, copper, and organochlorines at upstream, downstream, and discharge point of a dip site located on a flood zone. Arsenic (0 - 2,839 mg/kg), dieldrin (0 - 8.60 mg/kg), lindane (including by-products) (0 - 0.560 mg/kg), DDT (including metabolites) (0 - 1.200 mg/kg), and endrin (0 - 0.127 mg/kg) were the main contaminants detected in soil samples. Concentrations of As (0.9 - 32 mg/kg), dieldrin (0 - 0.038 mg/kg), and benzene hexachloride (α-BHC and β-BHC) (0 - 0.0031 mg/kg) were detected in stream sediments. Organochlorine was not detected in surface water. As in surface water ranged from 0 to 0.0021 g/m3, which was well below the maximum acceptable value (MAV) of 0.01 g/m3for potable drinking water supplies.

Arsenic concentrations in 142 soil samples were well above environmental guidelines for human habitation (30 mg/kg). Dieldrin recorded low to moderate contamination in soils with one sample exceeding the environmental guideline of 6 mg/kg. Arsenic in 4 of the 18 stream sediment samples were above the interim sediment quality low level guideline (ISQG-Low) of 20 mg/kg. Dieldrin concentrations in surface sediments up to 13 cm deep were well above the interim sediment quality high level guideline (ISQG-High) of 0.008 mg/kg. α-BHC and β-BHC had no ISQG guideline. The levels detected were above the lindane guideline (ISQG-High) of 0.001 mg/kg in surface sediments. Evidence of sheep dip chemicals moving away from a sheep dip site included arsenic, dieldrin, and DDT up to 100 m downhill from a dip site located on the margins of a steep slope with an adjacent gully. Elevated As was detected in stream sediments up to 40 m downstream of a dip site located on a flood zone. High level contamination from dieldrin, α-BHC, and β-BHC were recorded in downstream sediments. 

This study recommends that sheep dips located within 15 m of a stream and margins of steep slopes with an adjacent gully should be regarded as priority sites for contaminated land investigations that should include a monitoring programme.

text: Evaluating the potential of historic sheep dips as point sources of trace element and organochlorine pollutants Sheep dipping was a historic agricultural practice where sheep were immersed into insecticides to eradicate external parasites. Historical use of pesticides has caused localised soil contamination at former sheep dipping sites. There is limited information on offsite contamination such as in stream sediments, groundwater, and surface water. Predominant contaminants at historic sheep dipping sites are arsenic (As) and organochlorine (OC) compounds. There are estimated to be 50,000 former sheep dip sites in New Zealand, of which, over 10,000 are estimated to be in the Waikato Region.  Contamination at historical sheep dip sites is potentially concerning for human and environmental health.

The objectives of this study were to (1) evaluate a range of historic sheep dips to identify sites that had the highest leaching potential; (2) characterise the selected study sites; (3) establish the extent of contamination in soil, sediments, and water; (4) evaluate the extent of offsite contamination; and (5) assess compliance to environmental guideline limits.

Soil samples from two former sheep dip sites were analysed for arsenic, copper, and organochlorines at depths of up to 20 cm. Further soil samples were analysed for arsenic at depths of up to 7.5 cm. Stream water and sediment samples were analysed for arsenic, copper, and organochlorines at upstream, downstream, and discharge point of a dip site located on a flood zone. Arsenic (0 - 2,839 mg/kg), dieldrin (0 - 8.60 mg/kg), lindane (including by-products) (0 - 0.560 mg/kg), DDT (including metabolites) (0 - 1.200 mg/kg), and endrin (0 - 0.127 mg/kg) were the main contaminants detected in soil samples. Concentrations of As (0.9 - 32 mg/kg), dieldrin (0 - 0.038 mg/kg), and benzene hexachloride (α-BHC and β-BHC) (0 - 0.0031 mg/kg) were detected in stream sediments. Organochlorine was not detected in surface water. As in surface water ranged from 0 to 0.0021 g/m3, which was well below the maximum acceptable value (MAV) of 0.01 g/m3for potable drinking water supplies.

Arsenic concentrations in 142 soil samples were well above environmental guidelines for human habitation (30 mg/kg). Dieldrin recorded low to moderate contamination in soils with one sample exceeding the environmental guideline of 6 mg/kg. Arsenic in 4 of the 18 stream sediment samples were above the interim sediment quality low level guideline (ISQG-Low) of 20 mg/kg. Dieldrin concentrations in surface sediments up to 13 cm deep were well above the interim sediment quality high level guideline (ISQG-High) of 0.008 mg/kg. α-BHC and β-BHC had no ISQG guideline. The levels detected were above the lindane guideline (ISQG-High) of 0.001 mg/kg in surface sediments. Evidence of sheep dip chemicals moving away from a sheep dip site included arsenic, dieldrin, and DDT up to 100 m downhill from a dip site located on the margins of a steep slope with an adjacent gully. Elevated As was detected in stream sediments up to 40 m downstream of a dip site located on a flood zone. High level contamination from dieldrin, α-BHC, and β-BHC were recorded in downstream sediments. 

This study recommends that sheep dips located within 15 m of a stream and margins of steep slopes with an adjacent gully should be regarded as priority sites for contaminated land investigations that should include a monitoring programme.

year: 2015

title: Contextualizing Indigenous people and the state of exception: New Zealand's Waikeria Prison protest

authors: Martin, Jessica

abstract: On Tuesday, December 29, 2020, 16 protesters at Waikeria Prison, one of New Zealand's largest male prisons, engaged in a six-day standoff with prison guards to protest inhumane prison conditions. The Department of Corrections framed the event as an aimless riot, delegitimizing the intentional demonstration of resistance against state violence. Imprisoned intellectuals, specifically Imprisoned Black Radical tradition, have long examined and centered the prison as the harshest instrument of the state linked to the struggles of the collective. However, voices from imprisoned intellectuals are rarely considered in academic scholarship despite acute analysis of the state and liberation. This article employs the state of exception to contextualize the Waikeria protest. Particular attention is devoted to the ‘state of continuity,’ which allows for a broader understanding of a permanent state of racialized oppression and marginalization faced by Indigenous and Black communities in racialized-settler-colonial contexts. Populations designated as the exception are thus framed as a threat targeted for militaristic police intervention. This article concludes by extending the discussion of the state of continuity to include how expressions of rage and dissent by Indigenous and Black people are viewed as a direct threat to the sovereign order but are necessary for revolutionary change.

text: Contextualizing Indigenous people and the state of exception: New Zealand's Waikeria Prison protest On Tuesday, December 29, 2020, 16 protesters at Waikeria Prison, one of New Zealand's largest male prisons, engaged in a six-day standoff with prison guards to protest inhumane prison conditions. The Department of Corrections framed the event as an aimless riot, delegitimizing the intentional demonstration of resistance against state violence. Imprisoned intellectuals, specifically Imprisoned Black Radical tradition, have long examined and centered the prison as the harshest instrument of the state linked to the struggles of the collective. However, voices from imprisoned intellectuals are rarely considered in academic scholarship despite acute analysis of the state and liberation. This article employs the state of exception to contextualize the Waikeria protest. Particular attention is devoted to the ‘state of continuity,’ which allows for a broader understanding of a permanent state of racialized oppression and marginalization faced by Indigenous and Black communities in racialized-settler-colonial contexts. Populations designated as the exception are thus framed as a threat targeted for militaristic police intervention. This article concludes by extending the discussion of the state of continuity to include how expressions of rage and dissent by Indigenous and Black people are viewed as a direct threat to the sovereign order but are necessary for revolutionary change.

year: 2024-05-16