Presentation library


S-57 and the Presentation Model for ECDIS



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4.1 S-57 and the Presentation Model for ECDIS

The Presentation Model for ECDIS refers to the official IHO Transfer Standard for Digital Hydrographic Data (S-57) [6]. The IHO Transfer Standard states in Part 2, section 3;


The model described in this part of the Standard does not contain any rules for the presentation or display of information. It provides only the means for the factual description of the real world. The presentation of this information may vary to suit a particular use (e.g. it may be presented either graphically, using symbols, or in a textual form). Therefore, the presentation of information is considered to be independent of its storage. Different applications shall provide their own specific “presentation models”. A presentation model defines, via a set of presentation rules, the way in which real world information shall be displayed for a specified application. The concept of keeping information storage independent of presentation provides for greater versatility and flexibility. It allows the same data to be used for many purposes without requiring any change to its structure or content. If the presentation style or medium changes, only the presentation model has to be changed."
In contrast to a presentation model suitable for paper chart application, a presentation model to be used by ECDIS systems shall take into account the requirements of the IMO/IHO "Performance Standard for ECDIS" [2] and the IHO "Specifications for Chart Content and Display Aspects of ECDIS", IHO Publication S-52 [3]. In particular, this means, that the presentation of charts on an ECDIS screen changes depending on parameters and selections defined by the Mariner, such as safety contour, time of the day, traditional or simplified symbology, etc. Thus the presentation model shall cover not only colour and symbol definitions but also instructions how to handle a dynamically changing presentation as well.


4.2 Structure of the Presentation Model for ECDIS

The Presentation Model for ECDIS is built from two major parts:


- A library of colours, line styles, fill styles, point symbols and a set of symbology instructions and look-up tables for the translation of object descriptions into symbology instructions. This part is called "Presentation Library for ECDIS

- A description of the required programmable structure, which serves as a model for the graphic display within an ECDIS system and which explains how to use the elements of the Presentation Library and how to ensure the correct display of data structured according to S-57.




4.3 Supply and amendment of the Presentation Library

From edition 3.3 onwards the word-processed version of the Presentation Library is the "official" version. A digital version in .dai format is provided on the same CD-ROM as a manufacturer's option for edition 4.0.0. It consists of look-up tables; symbols; and colour tables and is supplied in ASCII format in the .dai file.


The name of the file on this CD which contains the official, word processed Presentation Library is "PSLBmm_n.pdf" where mm_n is the edition number.
IMPORTANT: The edition number of the PresLib installed shall be available to the Mariner on request.
The general layout of the Presentation Library is shown in section 4 of this publication. The various components of the Presentation Library are supplied and amended as follows:
The Presentation Library as a word processed file is issued on a CD-ROM, which carries a subscription charge for each new edition to help to cover maintenance costs. The word-processed Presentation Library includes:


  1. the look-up tables, colour tables and symbol library.




  1. the narrative and diagram conditional symbology procedures in UML form, together with symbolizing instructions (in section 13) for special IMO and IHO requirements which are needed to complete the symbolizing of an ENC,




  1. further information needed for implementing the above in ECDIS is given in all sections

On each occasion of an immediate amendment of the Presentation Library:




  1. a description of the items in the amendment will be freely available from the IHO web site under the Maintenance Section (www.iho.int > Publications > Download List) [11].




  1. the amended word-processed Presentation Library will be posted on the IHO web site (www.iho.int > Catalogue) together with the ECDIS Test Data Set (S-64) [10]. A subscription may be required.


Note: Only immediate amendments and not those of deferred amendments, will be included in the amended Presentation Library of .2 above.
The following digital files are also provided on the CD-ROM containing the word-processed Presentation Library:



  1. The .dai file of the Presentation Library, consisting of look-up tables, symbols and colour tables.


Note: The .dai version is provided as a manufacturer's option for edition 4.0.0, but may not be available for succeeding editions.
The "Test Edition Version" of the .dai file provided with old editions of the presentation library is no longer required in IEC 61174 and has been removed permanently from the digital Presentation Library. However symbol SY(CHKSYM01) has been retained for use in checking symbol size.



  1. ECDIS Chart 1 & Colour Differentiation Test Diagram, consisting of:




  • S-57 files containing a collection of all symbols coded as NEWOBJ using the SYMINS attribute and similarly arranged as INT1 [1] for paper charts

  • S-57 files containing combinations of foreground and background colours as line and area geometries.




  1. UML models of the CSPs in Enterprise Architect format


  1. Basic Concept of ECDIS Display

All elements of the Presentation Library are required to be implemented by a manufacturer unless otherwise stated. OEMs developing ECDIS display shall follow this documentation to perform the link between the S-57 feature object characteristic and the actual presentation on the ECDIS screen.


Fig 1 is an example of how the various elements of the Presentation Library can be linked together in order to display an S-57 object from the SENC. Only the individual elements (symbol library, look-up tables, etc.) are provided in the Presentation Library. The ECDIS manufacturer writes software linking the elements.
Section 10 gives further details of key functions that shall be taken into consideration by the ECDIS developer.


Fig 1. ECDIS display concept


Entry Point

Clipped portion of ENC to be displayed on the ECDIS screen. Perform for each SENC object.

Get Object from SENC

Object definition through attribute values and Spatial elements.

Is date within ranges: DATSTA - DATEND; PERSTA - PEREND?

Is the current date of presentation within the range of existence of the object?

I.e. if there are values of the attributes' pairs DATSAT - DATEND or PERSTA - PEREND then the current date is more than Start date and less than End date of the existence period of the object.



Get Symbology Instruction

Get symbology instructions, conditional instructions, priority value, radar flag, display category and viewing group from the appropriate line of the Look-up table file.

Instruction from Look-up Table

Take the Look-up Table file according to geometry type of the object and mariner parameters ('simplify point', 'pattern area boundaries')

Conditional Symbology?

Does a Conditional Symbology Procedure exist?

Generate Instruction from Symbology Procedure

Execute the conditional symbology procedure to get Symbology Instructions with parameters of presentations.

Procedure Library

Procedures to perform conditional symbology which may change priority, radar flag, display category and viewing group, set infinite SCAMIN value of the object.

Is display scale greater than or equal to 1/SCAMIN?

Is the current display scale greater than or equal to 1/SCAMIN value from the object?

Generate Entry to Display List from Symbology Instructions

Add graphical primitives to the display list taking into account Presentation parameters (priority, radar flag, display category and viewing group)

More Object?

Are there more objects in the SENC? If it is, go to the next object.

Perform Display List Commands



Mariner Options Section

E.g. safety contour, colour scheme, text on/off and etc.

Symbol Library

Simplified and full chart symbols, linestyles and patterns

Colour Tables

Colour tokens with XYL values for different palettes (Day, Dusk and Night palettes)

Final

Final presentation of the SENC

The basic concept of ECDIS display is as follows:


  1. The ECDIS determines which feature objects contained within the SENC are required for display.

  2. The ECDIS maintains a set of Mariner defined parameters (such as safety contour, safety depth, display category).

  3. Each feature object, whether point, line or area geometric primitive are transformed into symbolisation instructions using lookup tables and conditional symbology procedures described in this document.

  4. The symbolisation instructions are drawn to the screen using lookup tables to define colour values for the selected pallet and taking into account data-defined parameters which may affect display, such as DATSTA-DATEND and SCAMIN.

If, for example, the Mariner subsequently selects another safety contour, the list of symbolisation instructions are renewed and the depth areas distinguishing shades are changed by a symbology procedure which is called to generate symbology instructions for the object class DEPARE (depth area). There are many display options, some of which are mandatory and which are described in this document. The ECDIS manufacturer is also able to provide Mariner features within their ECDIS which build on the mechanisms described in this document.


Note that the ECDIS shall not initiate any change of state automatically or by linkage, e.g., it shall not automatically select “lights” because the Mariner selects the night colour table. All changes to the composition of the display shall be initiated by the Mariner.




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