title: Time-of-flight perception pipeline for selective green asparagus harvesting: Theory and application

authors: Peebles, Matthew Christopher Scott

subjects: Asparagus

abstract: Generally declining labour markets, coupled with a significant increase in the projected global population have raised concerns over a potential food scarcity crisis. In response to this, the agricultural industry is currently undergoing a technological revolution, especially with respect to robotic harvesting.
Green asparagus, due to its unique physiology and labour intensive harvesting requirements, has been a long-time crop of focus in this field. Despite the relatively large body of work surrounding the development of selective robotic asparagus harvesting solutions, no such machine has yet ascended to the level of being commercially competitive. A critical component of a prospective selective robotic asparagus harvester, that is missing from contemporary machines, is a robust vision system, capable of detecting, and localising, harvest-eligible spears in real-time from a commercial asparagus field.
This thesis presents a novel perception pipeline for time-of-flight images that can achieve this task, and describes the implementation of the proposed perception pipeline into two functional robotic harvesters, AHR-1 and AHR2, capable of harvesting green asparagus spears in a real-world commercial setting.
The proposed perception pipeline achieves spear detection by firstly, segmenting the soil plane from an input pointcloud of an asparagus row, generated with a time-of-flight camera. Two plane detection methods, namely RANSAC and a modified version Hyun’s method (MHM) were investigated for this purpose. A detailed evaluation of the performance of each method on cluttered scenes revealed both RANSAC and MHM to be suitable for soil plane segmentation of asparagus beds, with both methods demonstrating similar RMSE error across a variety of scenes. The stability of model predictions made by RANSAC was generally found to be lower than that achieved by MHM, particularly for high-clutter scenes. This was determined to be due to the non-deterministic nature of RANSAC coupled with high degrees of soil plane occlusion in high clutter scenes.
Following soil plane removal, non-asparagus points pertaining to rocks, weeds, and other field debris are then filtered from the scene. This is achieved by coarse filtering input points based on the output of a FRCNN model. The various FRCNN models utilised in this work were trained with a novel dataset of labelled images, collected from various asparagus farms throughout New Zealand and California, USA. Evaluation of these models revealed a typical maximum F1 score of 0.73, providing reasonable frame-by-frame identification of asparagus features.
The remaining point clusters, representing each asparagus spear in the scene, are then filtered to remove flying pixels; a typical artefact of time-of-flight imaging. A novel geometric filter, named the closest point filter (CP filter), was developed for this task. Based on laboratory testing, it was found that this filter achieved a 68% reduction in the mean standard deviation of intra-cluster distance with respect to ground-truth positions, resulting in a significant improvement in the accuracy of base point predictions.
The proposed perception pipeline is implemented inside a ROS framework, and deployed on two robotic harvesting platforms. The first platform, AHR-1, was developed as a proof-of-concept system. This system provided a wealth of knowledge which was utilised to develop a more complete prototype asparagus harvester, AHR-2. The design of AHR-1 and AHR-2 was largely informed by the shortcomings of existing asparagus harvesting robots from the literature, particularly with respect to their harvesting, and detection strategies.
The literature surrounding robotic asparagus harvesters does not provide an adequate method for objectively evaluating the performance of such systems. Consequentially, performance metrics pertaining to existing robotic harvesters are relatively opaque, particularly with respect to the selective nature of the harvesting task. These inadequacies necessitated the development of a novel evaluation method for the evaluation of a selective asparagus harvester, which was utilised to measure the performance of both AHR-1 and AHR-2.
Several field trials of AHR-1 and AHR-2 were conducted on farms throughout New Zealand and California, USA. The resulting analysis revealed that AHR-2 achieved state-of-the-art performance, harvesting 45.9% of all harvest eligible spears with a precision of 87.2% at its nominal ground speed of 0.3m/s. The vision system detected 97% of all harvest-eligible spears with a precision of 74.5% at this speed. When operating at a ground speed of 0.7m/s AHR 2’s harvesting rate fell to 22% with 95% precision. The corresponding drop in the vision systems detection rate was relatively small, dropping to 92.5% with 87.2% precision at a ground speed of 0.7m/s. From this it was concluded that the vision system outperformed the available hardware. The perception pipeline proposed by this thesis achieved state-of-the-art performance at a variety of ground speeds. The pipeline demonstrated a robustness to the unstructured nature of commercial asparagus fields, providing spear locations which successfully facilitated the robotic harvest of green asparagus spears.

text: Time-of-flight perception pipeline for selective green asparagus harvesting: Theory and application Generally declining labour markets, coupled with a significant increase in the projected global population have raised concerns over a potential food scarcity crisis. In response to this, the agricultural industry is currently undergoing a technological revolution, especially with respect to robotic harvesting.
Green asparagus, due to its unique physiology and labour intensive harvesting requirements, has been a long-time crop of focus in this field. Despite the relatively large body of work surrounding the development of selective robotic asparagus harvesting solutions, no such machine has yet ascended to the level of being commercially competitive. A critical component of a prospective selective robotic asparagus harvester, that is missing from contemporary machines, is a robust vision system, capable of detecting, and localising, harvest-eligible spears in real-time from a commercial asparagus field.
This thesis presents a novel perception pipeline for time-of-flight images that can achieve this task, and describes the implementation of the proposed perception pipeline into two functional robotic harvesters, AHR-1 and AHR2, capable of harvesting green asparagus spears in a real-world commercial setting.
The proposed perception pipeline achieves spear detection by firstly, segmenting the soil plane from an input pointcloud of an asparagus row, generated with a time-of-flight camera. Two plane detection methods, namely RANSAC and a modified version Hyun’s method (MHM) were investigated for this purpose. A detailed evaluation of the performance of each method on cluttered scenes revealed both RANSAC and MHM to be suitable for soil plane segmentation of asparagus beds, with both methods demonstrating similar RMSE error across a variety of scenes. The stability of model predictions made by RANSAC was generally found to be lower than that achieved by MHM, particularly for high-clutter scenes. This was determined to be due to the non-deterministic nature of RANSAC coupled with high degrees of soil plane occlusion in high clutter scenes.
Following soil plane removal, non-asparagus points pertaining to rocks, weeds, and other field debris are then filtered from the scene. This is achieved by coarse filtering input points based on the output of a FRCNN model. The various FRCNN models utilised in this work were trained with a novel dataset of labelled images, collected from various asparagus farms throughout New Zealand and California, USA. Evaluation of these models revealed a typical maximum F1 score of 0.73, providing reasonable frame-by-frame identification of asparagus features.
The remaining point clusters, representing each asparagus spear in the scene, are then filtered to remove flying pixels; a typical artefact of time-of-flight imaging. A novel geometric filter, named the closest point filter (CP filter), was developed for this task. Based on laboratory testing, it was found that this filter achieved a 68% reduction in the mean standard deviation of intra-cluster distance with respect to ground-truth positions, resulting in a significant improvement in the accuracy of base point predictions.
The proposed perception pipeline is implemented inside a ROS framework, and deployed on two robotic harvesting platforms. The first platform, AHR-1, was developed as a proof-of-concept system. This system provided a wealth of knowledge which was utilised to develop a more complete prototype asparagus harvester, AHR-2. The design of AHR-1 and AHR-2 was largely informed by the shortcomings of existing asparagus harvesting robots from the literature, particularly with respect to their harvesting, and detection strategies.
The literature surrounding robotic asparagus harvesters does not provide an adequate method for objectively evaluating the performance of such systems. Consequentially, performance metrics pertaining to existing robotic harvesters are relatively opaque, particularly with respect to the selective nature of the harvesting task. These inadequacies necessitated the development of a novel evaluation method for the evaluation of a selective asparagus harvester, which was utilised to measure the performance of both AHR-1 and AHR-2.
Several field trials of AHR-1 and AHR-2 were conducted on farms throughout New Zealand and California, USA. The resulting analysis revealed that AHR-2 achieved state-of-the-art performance, harvesting 45.9% of all harvest eligible spears with a precision of 87.2% at its nominal ground speed of 0.3m/s. The vision system detected 97% of all harvest-eligible spears with a precision of 74.5% at this speed. When operating at a ground speed of 0.7m/s AHR 2’s harvesting rate fell to 22% with 95% precision. The corresponding drop in the vision systems detection rate was relatively small, dropping to 92.5% with 87.2% precision at a ground speed of 0.7m/s. From this it was concluded that the vision system outperformed the available hardware. The perception pipeline proposed by this thesis achieved state-of-the-art performance at a variety of ground speeds. The pipeline demonstrated a robustness to the unstructured nature of commercial asparagus fields, providing spear locations which successfully facilitated the robotic harvest of green asparagus spears.

year: 2021

title: Environmental pollutants from the Scott and Shackleton expeditions during the ‘Heroic Age’ of Antarctic exploration

authors: Blanchette, Robert A.

subjects: Antarctica

abstract: Early explorers to Antarctica built wooden huts and brought huge quantities of supplies and equipment to support their geographical and scientific studies for several years. When the expeditions ended and relief ships arrived, a rapid exodus frequently allowed only essential items to be taken north. The huts and thousands of items were left behind. Fuel depots with unused containers of petroleum products, asbestos materials, and diverse chemicals were also left at the huts. This investigation found high concentrations of polyaromatic hydrocarbons in soils under and around the historic fuel depots, including anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, fluorene, and pyrene, as well as benzo[a]anthracene, benzo[a]pyrene, and fluoranthene, which are recognized carcinogens. Asbestos materials within the huts have been identified and extensive amounts of fragmented asbestos were found littering the ground around the Cape Evans hut. These materials are continually abraded and fragmented as tourists walk over them and the coarse scoria breaks and grinds down the materials. A chemical spill, within the Cape Evans hut, apparently from caustic substances from one of the scientific experiments, has caused an unusual deterioration and defibration on affected woods. Although these areas are important historic sites protected by international treaties, the hazardous waste materials left by the early explorers should be removed and remedial action taken to restore the site to as pristine a condition as possible. Recommendations are discussed for international efforts to study and clean up these areas, where the earliest environmental pollution in Antarctica was produced.

text: Environmental pollutants from the Scott and Shackleton expeditions during the ‘Heroic Age’ of Antarctic exploration Early explorers to Antarctica built wooden huts and brought huge quantities of supplies and equipment to support their geographical and scientific studies for several years. When the expeditions ended and relief ships arrived, a rapid exodus frequently allowed only essential items to be taken north. The huts and thousands of items were left behind. Fuel depots with unused containers of petroleum products, asbestos materials, and diverse chemicals were also left at the huts. This investigation found high concentrations of polyaromatic hydrocarbons in soils under and around the historic fuel depots, including anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, fluorene, and pyrene, as well as benzo[a]anthracene, benzo[a]pyrene, and fluoranthene, which are recognized carcinogens. Asbestos materials within the huts have been identified and extensive amounts of fragmented asbestos were found littering the ground around the Cape Evans hut. These materials are continually abraded and fragmented as tourists walk over them and the coarse scoria breaks and grinds down the materials. A chemical spill, within the Cape Evans hut, apparently from caustic substances from one of the scientific experiments, has caused an unusual deterioration and defibration on affected woods. Although these areas are important historic sites protected by international treaties, the hazardous waste materials left by the early explorers should be removed and remedial action taken to restore the site to as pristine a condition as possible. Recommendations are discussed for international efforts to study and clean up these areas, where the earliest environmental pollution in Antarctica was produced.

year: 2004

title: Maori participation in higher education: Tainui graduates from the University of Waikato, 1992 to 1997

authors: Tiakiwai, Sarah-Jane

abstract: This thesis is an examination of what factors contribute to the success of Maori who participate in higher education. The thesis is informed by the experiences of nine Tainui tribal members who received scholarships from the Tainui Maori Trust Board and who graduated from the University of Waikato between 1992 and 1997. 

The thesis addresses two questions: what factors contributed to the success of Tainui graduates at the University of Waikato? What effect did programmes, policies and initiatives offered by the University of Waikato and the Tainui Maori Trust Board have on the academic success of Tainui graduates at the University of Waikato? 

There are three main components to the thesis: a brief history of the University of Waikato and an examination of three documents (University of Waikato Charter 1991; Paetawhiti, the strategic plan 1993; Academic Audit Unit report 1997) and how they pertain to Maori; a history of the Tainui Maori Trust Board and an examination of the Tainui Education Strategy (1986, 1991), its review (1993) and scholarship programmes; and a study and analysis of the experiences of nine Tainui graduates from the University of Waikato. 

Argued from an eclectic theoretical and methodological position, drawing from indigenous and western theories and research practices that emphasise a kaupapa Maori and tribal approach, the thesis identifies multiple factors that have contributed to the success of the Tainui graduates. These factors include family and parental support, mentoring, the role of finances, institutional support, and identity. 

The thesis finds through examination of the documents, that the policies, initiatives and programmes of the Tainui Maori Trust Board and the University of Waikato have ambiguous and at times conflicting aims and objectives in regard to Maori participation and graduation from higher education. The thesis also finds that the experiences of the graduates reveal that neither the Tainui Maori Trust Board nor policies relating to Maori at the University of Waikato played significant roles in the success of the Tainui graduates. Rather, the thesis finds that the success of the graduates is largely borne by their own efforts, which reflect western notions of success, but which also reinforce their identity as Maori, and as Tainui tribal members. 

The thesis suggests that both the Tainui Maori Trust Board and the University of Waikato review their relationships with their tribal and Maori members (respectively), and recommendations are made to help develop a greater awareness of the contribution that both organisations can make to the success of Maori university students.

text: Maori participation in higher education: Tainui graduates from the University of Waikato, 1992 to 1997 This thesis is an examination of what factors contribute to the success of Maori who participate in higher education. The thesis is informed by the experiences of nine Tainui tribal members who received scholarships from the Tainui Maori Trust Board and who graduated from the University of Waikato between 1992 and 1997. 

The thesis addresses two questions: what factors contributed to the success of Tainui graduates at the University of Waikato? What effect did programmes, policies and initiatives offered by the University of Waikato and the Tainui Maori Trust Board have on the academic success of Tainui graduates at the University of Waikato? 

There are three main components to the thesis: a brief history of the University of Waikato and an examination of three documents (University of Waikato Charter 1991; Paetawhiti, the strategic plan 1993; Academic Audit Unit report 1997) and how they pertain to Maori; a history of the Tainui Maori Trust Board and an examination of the Tainui Education Strategy (1986, 1991), its review (1993) and scholarship programmes; and a study and analysis of the experiences of nine Tainui graduates from the University of Waikato. 

Argued from an eclectic theoretical and methodological position, drawing from indigenous and western theories and research practices that emphasise a kaupapa Maori and tribal approach, the thesis identifies multiple factors that have contributed to the success of the Tainui graduates. These factors include family and parental support, mentoring, the role of finances, institutional support, and identity. 

The thesis finds through examination of the documents, that the policies, initiatives and programmes of the Tainui Maori Trust Board and the University of Waikato have ambiguous and at times conflicting aims and objectives in regard to Maori participation and graduation from higher education. The thesis also finds that the experiences of the graduates reveal that neither the Tainui Maori Trust Board nor policies relating to Maori at the University of Waikato played significant roles in the success of the Tainui graduates. Rather, the thesis finds that the success of the graduates is largely borne by their own efforts, which reflect western notions of success, but which also reinforce their identity as Maori, and as Tainui tribal members. 

The thesis suggests that both the Tainui Maori Trust Board and the University of Waikato review their relationships with their tribal and Maori members (respectively), and recommendations are made to help develop a greater awareness of the contribution that both organisations can make to the success of Maori university students.

year: 2001