Christos Kastrisios | National Technical University of Athens (original) (raw)

Papers by Christos Kastrisios

Geographic Information Science & Technology Body of Knowledge, 2022

Cartography and Geographic Information Science, 2022

Hydrographic sounding selection is the process of generalizing high-resolution... more Hydrographic sounding selection is the process of generalizing high-resolution bathymetry data to a more manageable subset capable of supporting nautical chart compilation or bathymetric modeling, and thus, is a fundamental task in nautical cartography. As technology improves and bathymetric data are collected at higher resolutions, the need for automated generalization algorithms that respect nautical cartographic constraints increases, since errors in this phase are carried over to the final product. Currently, automated algorithms for hydrographic sounding selection rely on radius- and grid-based approaches; however, their outputs contain a dense set of soundings with a significant number of cartographic constraint violations, thus increasing the burden and cost of the subsequent, mostly manual, cartographic sounding selection. This work presents a novel label-based generalization algorithm that utilizes the physical dimensions of the symbolized depth values on charts to avoid the over-plot of depth labels at scale. Additionally, validation tests based on cartographic constraints for nautical charting are implemented to compare the results of the proposed algorithm to radius and grid-based approaches. It is shown that the label-based generalization approach best adheres to the constraints of functionality (safety) and legibility.

Charted bathymetry encompasses the cartographer's effort to accurately describe submarine top... more Charted bathymetry encompasses the cartographer's effort to accurately describe submarine topography based on the source information. A key factor in the selection process is that, at any location, the charted features do not give a false impression that the water depth is deeper than it actually is. Our research work focused on development of an automated solution for the identification of locations where this goal is violated. We present the research work from conceptualization to the development of an ArcGIS Toolbox named "Sounding Validation Toolbox" that consists of three automated tools, as well as the challenges and results in the process of making it operational with the Marine Chart Division of NOAA/Office of Coast Survey.

The Electronic Navigational Chart (ENC) consists of point, line, and area features compiled follo... more The Electronic Navigational Chart (ENC) consists of point, line, and area features compiled following the node-chain topological model. To ensure that the topological structure is valid, the International Hydrographic Organization (IHO) has developed a number of checks defined in Publication S-58. Many of the checks deal with the vertical component of the nautical chart with the aim to validate consistency among compiled geo-objects. Nevertheless, validation checks are not exhaustive and spatial relationships may be violated. The presented work identifies vertical discontinuities between depth areas and adjoining geo-objects in the ENC and following an iterative approach proposes fixes to the attributes and the geometry of the depth areas with errors.

Most navigational charts are an amalgamation of geospatial information of varying quality collect... more Most navigational charts are an amalgamation of geospatial information of varying quality collected using different techniques at different times. Data collected with high resolution multi-beam echo sounders or lidar systems may co-exist on the chart with data collected with lead-line as far back as the 18th century. Data quality on charts is currently provided as a series of Category Zone of Confidence (CATZOC) values. For every part of the chart, CATZOC values provide information about the horizontal and vertical uncertainty of bathymetric information, as well as the seabed coverage and feature detection. CATZOC is portrayed in ECDIS as an additional layer with glyphs using a rating system of stars: six to two stars for the best to lowest quality data and "U" for unassessed data. With the provided information mariners may interpret the seabed morphology, identify shoals that pose a threat for the plotted voyage, and select routes that maintain under-keel clearance, howev...

Depth curves and charted soundings are two structural components of nautical charts, both derived... more Depth curves and charted soundings are two structural components of nautical charts, both derived from a more detailed dataset through generalization. Once depth curves are generated, the cartographer makes a selection of soundings that complements the depth curves and other features carrying bathymetric information in the adequate representation of the seabed morphology at the scale of the product. The selection of charted soundings-which is currently either performed fully manually, or partially manually using a computer-assisted solution-must meet the safety constraint, i.e., that no source sounding exists that is shoaler than what the mariner would expect by mentally interpolating the charted bathymetric information. According to International Hydrographic Organization S-4 publication, for well-surveyed areas that is achieved through the "triangular method of selection" and consists of two tests: the Triangle Test and the Edge Test. There are currently no fully automated solutions, so, with the ultimate goal of supporting "cartography at point of use", we consider the problem of automating the validation of shoal-selected soundings. We discuss an implementation of the triangle test with improved performance near linear features, the first automated implementation of the edge test, and that the edge test may identify shoals that the triangle test fails to detect, confirming its significance in the validation process. We demonstrate an "intrinsic" limitation of the two tests that makes infeasible a fully automated solution based solely on the two tests. Finally, to overcome the intrinsic limitation, we propose a new validation test, named Nautical Surface Test, that captures the local morphology at the appropriate charting resolution as the solution for the automated validation of the charted bathymetric information.

The selection of soundings to be shown on nautical charts is one of the most important and compli... more The selection of soundings to be shown on nautical charts is one of the most important and complicated tasks in nautical cartography. From the vast number of source soundings the cartographer is called to select all those important for the safety of navigation and to verify the "shoal biased" pattern of selection against the source soundings. A longterm goal of the cartographic community has been the automation of the tasks involved in nautical chart production, including that of the selection and validation of charted soundings. With the aim to contribute to that effort, this paper presents an implementation of the triangle test for the automated validation of selected soundings which has improved performance on the detection of shoals near depth curves and coastlines.

The 1982 United Nations Convention on the Law of the Sea (UNCLOS) is the document that serves as ... more The 1982 United Nations Convention on the Law of the Sea (UNCLOS) is the document that serves as the public and customary law, codifies the various maritime zones and their regime. Jurisdiction over maritime zones is important in terms of security, exploration and exploitation of natural resources, international relations and effective ocean management. Scientists and professionals from a variety of disciplines are concerned with maritime zones, the legal and the technical aspects of the competing interests among coastal states. However, of great importance is the technical expert himself who is responsible for taking full account of the provisions and requirements of UNCLOS, advice and inform the governments on its technical aspects and employ methods for delineating maritime outer limits in accordance to its provisions. The present paper is concerned with the delimitation methodologies proposed by cartographers and applied by States and juridical bodies, with respect both unilateral and bilateral limits and aims at contributing to an update to the relevant literature by providing detailed guidelines on how to construct the outer limits graphically.

acquiring, processing, analysing, accessing, and presenting hydrographic data can be easily added... more acquiring, processing, analysing, accessing, and presenting hydrographic data can be easily added when required (IHO,2015). Following the adoption of S-100, many product specifications are under development by the IHO S-100 specialized Working Groups (WGs) including S-101 for Electronic Navigational Charts (ENCs) and S-121 for Maritime Limits and Boundaries.

Proceedings of the ICA, 2021

Safety of navigation is essential for the global economy as maritime trade accounts for more than... more Safety of navigation is essential for the global economy as maritime trade accounts for more than 80% of international trade. Carrying goods by ship is economically and environmentally efficient, however, a maritime accident can cause harm to the environment and local economies. To ensure safe passage, mariners tend to use already familiar routes as a best practice; most groundings occur when a vessel travels in unfamiliar territories or suddenly changes its route, e.g., due to extreme weather. In highly trafficked areas, the highest risk for ships is that of collision with other vessels in the area. In these situations, a network of previously traversed routes could help mariners make informed decisions for finding safe alternative routes to the destination, whereas a system that can predict the routes of nearby vessels would ease the burden for the mariner and alleviate the risk of collision. The goal of this project is to utilize Automatic Identification System data to create a network of "roads" to promote a route planning and prediction system for ships that makes finding optimal routes easier and allows mariners on the bridge and Autonomous Surface Vehicles to predict movement of ships to avoid collisions. This paper presents the first steps taken toward this goal, including data processing through the usage of Python libraries, database design and development utilizing PostgreSQL, density map generation and visualizations through our own developed libraries, an A* pathfinding algorithm implementation, and an early implementation of an Amazon Web Services deployment.

Depth areas are utilized by the Electronic Chart Display and Information Systems (ECDIS) along wi... more Depth areas are utilized by the Electronic Chart Display and Information Systems (ECDIS) along with the vessel’s characteristics (e.g., draft, squat) and other situational information (e.g., tides) for separating safe areas from those unsafe to navigate. Any error in their compilation is carried over to the analysis performed in the ECDIS. As a result, waters may be portrayed deeper, thus posing a risk to the vessel navigating them, or may appear shoaler, thus triggering useless ECDIS alarms which contribute to the situation known as “mariner’s deafness”. With the exception of crisp boundaries where abrupt changes are expected, the transition between depth areas should be smooth and continuous. In this paper we present a research toward a mechanism for identifying discontinuities and an error remediation approach that proposes changes to the encoded depth range and the geometry of depth areas with identified discontinuities, for the cartographer’s attention.

Navigational charts contain a combination of geospatial information of varying quality collected ... more Navigational charts contain a combination of geospatial information of varying quality collected at different times using various techniques. Bathymetric data quality is mainly encoded in electronic charts with the Category of Zones of Confidence (CATZOC). CATZOC provides information about the horizontal and vertical uncertainty of depth information, as well as the seabed coverage and feature detection. It is visualized in Electronic Chart Display and Information Systems (ECDIS) as an additional layer with glyphs using a rating system of stars: six to two stars for the best to lowest quality data and “U” for unassessed data. The current symbology creates visual clutter which is worse in areas of high quality bathymetry. Furthermore, horizontal and vertical uncertainties may not be adequately assessed by the user. This paper presents a research program aimed at the development of a method for portraying bathymetric data quality and for integrating the quantified uncertainties in ECDIS.

The Electronic Navigational Chart (ENC) consists of point, line, and area features compiled follo... more The Electronic Navigational Chart (ENC) consists of point, line, and area features compiled following the nodechain topological model. To ensure that the topological structure is valid, the International Hydrographic Organization (IHO) has developed a number of checks defined in Publication S-58. Many of the checks deal with the vertical component of the nautical chart with the aim to validate consistency among compiled geoobjects. Nevertheless, validation checks are not exhaustive and spatial relationships may be violated. The presented work identifies vertical discontinuities between depth areas and adjoining geo-objects in the ENC and following an iterative approach proposes fixes to the attributes and the geometry of the depth areas with errors. Keywords— ENC validation checks; automated nautical cartography; digital terrain modelling; topographic surface; nautical surface; surface reconstruction;

Marine Policy, 2017

Abstract This paper is concerned with the implementation and realisation of a Worldwide Electroni... more Abstract This paper is concerned with the implementation and realisation of a Worldwide Electronic Navigational Charts Database (WEND), adopted by the International Hydrographic Organization (IHO) and its members in supporting marine navigation. It identifies the issue of gaps and overlaps between adjoining Electronic Navigational Charts (ENCs) and explores its consequences to the operation of Electronic Chart Display and Information Systems (ECDIS) and the fulfilment of International Maritime Organization (IMO) chart carriage requirements. As the ENCs production is directly dependent on states’ cartographic competences, this paper delves into the coastal states’ jurisdiction in accordance with international law of the sea, and in particular the United Nations Convention on the Law of the Sea, and ΙΗΟ and IMO instruments. Through a case study on recently produced ENCs in the Mediterranean and more specifically in the Aegean Sea, this paper documents the necessity to respect states’ cartographic competences in realising the WEND concept and cautions that, otherwise, new and extended overlaps emerge, which pose a risk to the safety of navigation, and, at the same time, become means through which states may promote their geopolitical aspirations as to jurisdiction over certain marine areas.

Ocean & Coastal Management, 2016

Abstract The delimitation of maritime zones and boundaries foreseen by the United Nations Convent... more Abstract The delimitation of maritime zones and boundaries foreseen by the United Nations Convention on the Law of the Sea is a factor of economic growth, effective management of the coastal and ocean environment and the cornerstone for maritime spatial planning. Maritime boundaries form the outermost limits of coastal states and their accurate computation is a matter of national priority. The final delimitation agreement is ultimately a political decision; however the cartographer/GIS expert should portray the zones’ limits with the best possible accuracy. Existing applications tend to address this issue with their weakness being that the delimitation is a complex and time-consuming process. There, the subject is addressed in a fragmented way with the user composing the outer limits from partial results. This paper presents a cohesive methodology for the automated delimitation of the median lines and maritime zones between all states in a region based on the Voronoi tessellation of maritime space. Furthermore, through a case study, it presents and evaluates the results of this methodology and its implementation and demonstrates its ability to delimit the zones and boundaries, unilaterally and bilaterally, without the user’s intervention.

Ocean & Coastal Management, 2016

Abstract One of the fundamental concepts of the Convention on the Law of the Sea is that of the b... more Abstract One of the fundamental concepts of the Convention on the Law of the Sea is that of the baselines, where from the breadth of the maritime zones is measured. Baselines, delimiting the land and internal waters from the sea, can be any combination of normal, straight, archipelagic or bay-closing lines. The determination of the coastline indentations at which the coastal State is entitled to draw bay-closing lines has been a complicated and time-consuming task. Existing GIS environments carry out the process semi-automatically with the user undertaking the location of the candidate indentation and the software validating the length and semi-circle criteria stipulated by the Convention. This process has the inherent weakness that indentations meeting both criteria may remain undetected. This paper presents, implements and evaluates a methodology for the determination of all indentations along the coastline that can be closed with bay-closing lines without the intervention of the user. The proposed methodology addresses the issue of juridical bays in its entirety, including the existence or absence of headlands, the presence of islands in the mouth of the bay, as well as the maximization of the area of the bay, something that currently available solutions are lacking in.

Proceedings of the ICA, May 16, 2018

The delimitation of maritime zones and boundaries foreseen by the United Nations Convention on th... more The delimitation of maritime zones and boundaries foreseen by the United Nations Convention on the Law of the Sea (UNCLOS) is a factor of economic growth, effective management of the coastal and ocean environment and the cornerstone for maritime spatial planning. Maritime zones and boundaries form the outermost limits of coastal states and their accurate delineation and cartographic portrayal is a matter of national priority. Although UNCLOS is a legal document, its implementation-at first place-is purely technical and requires-amongst others-theoretical and applied background on Geodesy, Cartography and Geographic Information Systems (GIS) for those involved. This paper provides a brief historical background of the evolution of the UNCLOS, presents the various concepts of the Convention and identifies the problems inherent in the maritime delimitation process. Furthermore, it presents solutions that will facilitate the cartographer's work in order to achieve unquestionable results. Through the paper it becomes evident that the role of the cartographer and the GIS expert is critical for the successful implementation of maritime delimitation.

Geographic Information Science & Technology Body of Knowledge, 2022

Cartography and Geographic Information Science, 2022

Proceedings of the ICA, 2021

The Electronic Navigational Chart (ENC) consists of point, line, and area features compiled follo... more The Electronic Navigational Chart (ENC) consists of point, line, and area features compiled following the nodechain topological model. To ensure that the topological structure is valid, the International Hydrographic Organization (IHO) has developed a number of checks defined in Publication S-58. Many of the checks deal with the vertical component of the nautical chart with the aim to validate consistency among compiled geoobjects. Nevertheless, validation checks are not exhaustive and spatial relationships may be violated. The presented work identifies vertical discontinuities between depth areas and adjoining geo-objects in the ENC and following an iterative approach proposes fixes to the attributes and the geometry of the depth areas with errors. Keywords— ENC validation checks; automated nautical cartography; digital terrain modelling; topographic surface; nautical surface; surface reconstruction;

Marine Policy, 2017

Ocean & Coastal Management, 2016

Proceedings of the ICA, May 16, 2018