COLREGs-Compliant ASV Path Planning in River

COLREGs- Compliant ASV Path Planning in Riverbutton5

By: Mei Jian Hong (PhD Student)

 

1.Introduction

The COLREGs consists of five parts and 38 rules. ‘Part A: General’ is the regulations of the application and responsibility. ‘Part B: Steering and sailing’ regulates the rules of marine crafts navigation. ‘Part C: Lights and shapes’ regulates the use of lighting signals. ‘Part D’ is Sound and light signals and ‘Part E’ is Exemption.

Rules 13 to 15 in Part B regulate three scenarios, i.e. overtaking, head-on and crossing, which are as follows.

 

Rule 13. Overtaking:

An overtaking vessel must keep out of the way of the vessel being overtaken.

Rule 14. Head-on situations:

When two power-driven vessels are meeting head-on both must alter course to starboard so that they pass on the port side of the other.

Rule 15. Crossing situations:

When two power-driven vessels are crossing, the vessel which has the other on the starboard side must give way and avoid crossing ahead of her.

Besides, Rule 9 regulates the narrow channel waterway, such as riverine environment.

Rule 9. Narrow channels:

A vessel proceeding along a narrow channel must keep to starboard.

Small vessels or sailing vessels must not impede (larger) vessels which can navigate only within a narrow channel.

Ships must not cross a channel if to do so would impede another vessel which can navigate only within that channel.

In summary, the ASV has to make an evasive manoeuvre and avoid the encountered obstacles from starboard side.

 

2.COLREGs-Compliant ASV Path Planning in River

5a nov15

(a) overtaking

5b nov15

(b) head on

 

Figure 1. Simulation of overtaking and head-on scenarios

 

Figure 1 shows the simulation results of the COLREGs-compliant path planning in overtaking and head-on scenarios. The ASV is forced to bypass the static and dynamic obstacles from starboard side, which is compliant with COLREGs.

 

Reference(s):

  1. https://en.wikipedia.org/wiki/International_Regulations_for_Preventing_Collisions_at_Sea
  2. http://www.imo.org/en/About/Conventions/ListOfConventions/Pages/COLREG.aspx


                                                      

Underwater Acoustic Source Localization

Underwater Acoustic Source Localizationbutton4

By: Mad Helmi Bin Ab. Majid (PhD Student)

 

 

Target localization is a branch of underwater localization research which related to the study of how to determine position of underwater target of interest with respect to a known reference point. Global positioning system (GPS) has been used for decades to determine position located on the ground by using multilateration principles from multiples satellites. Unfortunately, GPS unable to work in underwater environment due to poor penetration of radio signal. Luckily, acoustic signal travel well within the water column with speed of approximately 1500 m/s which is about four times faster than speed on the surface. Underwater acoustic pinger localization is one of the research topic related to the underwater localization. The working principle of the acoustic source localization is shown in the following figure. From the figure, three different phenomena of acoustic source localization could be observed:

  1. Firstly, absolute localization of the stationary target directly from surface vessel. In this case, all measurement taken or estimate with respect to position of the surface vessel based on acoustic signaling. Since position of the vessel is determined by the GPS, absolute position of the pinger source could be determined.
  2. Secondly, absolute localization of mobile acoustic target (in this case underwater vehicle) is performed directly form surface vessel based acoustic signaling. The only difference from the previous phenomena is the acoustic pinger is carried by underwater vehicle which is considered as mobile acoustic source.
  3. Thirdly, relative localization of the stationary target with respect to the position of the underwater vehicle. At this stage, this localization is considered relative since the underwater vehicle does not carry any GPS receiver. However, since underwater vehicle itself is localized by surface vessel through underwater acoustic positioning, the absolute positioning could be obtained. This method of localization is commonly used for deep water application where variation of sound speed and water depth is significant.

4a nov15

The Hurwitz Stability Criterion

The Hurwitz Stability Criterionbutton2

By: Song Yoong Siang (PhD Student)

 

 

2e nov15 degree polynomial, 2a nov15 of the form shown by Equation (1) is stable if all roots of this polynomial lie in the left half of the complex plane. In this situation, any solution to the linear, homogeneous differential equation will converge to zero. However, it is difficult to determine all the roots if 2b nov15 is large. The Hurwitz test provides a necessary and sufficient condition for stability without solving the Equation (2).

2c nov15(1)

    2d nov15(2)

The Hurwitz matrix for 2e nov15 degree polynomial is describe in Equation (3). 2a nov15 is stable if and only if the leading principal minors of 2f nov15 are all positive.The leading principal minors, 2g nov15 are the determinants of the upper left (1×1), (2×2), . . ., (n×n) submatrices of 2f nov15. Example of leading principal minors are shown in Equation (4) – (6).

2h nov15(3)

 

2i nov15(4)

 

2j nov15(5)

 

2k nov15

 

Reference(s):

  1. http://www.systems.caltech.edu/EE/Courses/EE32b/handouts/Hurwitz.pdf
  2. http://www.cems.uvm.edu/~tlakoba/08_fall/EE_295/Routh_Hurwitz_Criterion.pdf
  3. http://planetmath.org/sites/default/files/texpdf/35395.pdf

Visual Servoing Graphical User Interface

Visual Servoing Graphical User Interfacebutton3

By: Mohd Faid Bin Yahya (PhD Student)

 

This article is about the design of graphical user interface or simply known as GUI in visual servoing system. Basically, in any vision system, there will be at least 2 image display windows. One window is used to display original image while another one windowused to display processed image. Fig. 1 shows image display widgets where (a) is original image and (b) is processed image. Notice that Fig. 1 (a) also has user interface for tracking cursor in (X, Y) coordinate format, color values (H, S, V) if click event is triggered in the image display, and the speed of the camera in frame per second or FPS. Additionally, Fig. 1 (b) has user interface to display processed image for options after HSV conversion, morphology operation, when locating contour, and when tracking contour of detected markers.

 

              3a nov15      (a)

            

  3b nov15

                                                                                           (b)                                                                                      

                                                                     Fig. 1.Image display widgets: (a) original image (b) processed image.

 

Fig. 2 is an example of vision system widget. The widget shows that there is HSV FILTER to convert image from Red-Green-Blue (RGB) channel to Hue-Saturation-Value (HSV) channel. There are slider bars user interface for H, S, and V for their min-max values that user want to filter out. Below HSV FILTER user interface is MORPHOLOGY OPENING user interface so that erosion and dilation can be performed on the processed image. Then, there is also CAMERA CONTROL / SETTING to start image capture device, or save, or load a video file. Subsequently, HSV MARKER will display info regarding the values for RGB to HSV conversion. Finally, VISUAL SERVO controls are used to get desired image for visual servoing system. This desired image will be compared to current captured image so that a robot will adjust its body by minimizing the error between desired and current images.

 

3c nov15

Fig. 2.Vision system widget.

 

Note that the GUI shown in this article is designed using Qt user interface, programmed in C++.

 

 

 

 

Marine Traffic Rules- COLREGs

Marine Traffic Rules- COLREGsbutton5

By: Mei Jian Hong (PhD Student)

 

  1. Introduction

 

The International Regulations for Preventing Collisions at Sea 1972 (COLREGs) are published by the International Maritime Organization (the IMO) as Marine Traffic Rules to be followed by ships and other vessels to prevent collisions between two or more vessels. COLREGs are subject to their own navigation rules, and coastal waterways, which are subject to international navigation rules at sea and inland waterways.

The 1972 Convention was designed to update and replace the Collision Regulations of 1960 which were adopted at the same time as the 1960 SOLAS Convention.

One of the most important innovations in the 1972 COLREGs was the recognition given to traffic separation schemes - Rule 10 gives guidance in determining safe speed, the risk of collision and the conduct of vessels operating in or near traffic separation schemes.

The first such traffic separation scheme was established in the Dover Strait in 1967. It was operated on a voluntary basis at first but in 1971 the IMO Assembly adopted a resolution stating that that observance of all traffic separation schemes be made mandatory - and the COLREGs make this obligation clear.

    2. Content of COLREGs

Although rules for navigating vessels inland may differ, the international rules specify that they should be as closely in line with the international rules as possible. In most of continental Europe, the Code Européen des Voies de la Navigation Intérieure (CEVNI, or the European Code for Navigation on Inland Waters) apply. In the United States, the rules for vessels navigating inland are published alongside the international rules.

The COLREGs include 38 rules divided into five sections: Part A - General; Part B - Steering and Sailing; Part C - Lights and Shapes; Part D - Sound and Light signals; and Part E - Exemptions. There are also four Annexes containing technical requirements concerning lights and shapes and their positioning; sound signaling appliances; additional signals for fishing vessels when operating in close proximity, and international distress signals.

 

Reference(s):

  1. https://en.wikipedia.org/wiki/International_Regulations_for_Preventing_Collisions_at_Sea
  2. http://www.imo.org/en/About/Conventions/ListOfConventions/Pages/COLREG.aspx