The radar image overlay can be generated by using either one intensity colour or a range of intensities. The colour for high echo intensity (RADHI) shall be used where only one intensity is used. If you prefer to show more than one echo intensity or fading target trails, the corresponding colour intensities shall be interpolated between the colour for high echo intensity (RADHI) and the colour for low echo intensity (RADLO). A separate colour token is used for ARPA targets and information tagged on them (ARPAT).
Optionally, the manufacturer may vary the radar green overlay by making it transparent. As described in section 8.4.2, there are two ways of doing this:
1) Use "pixel swap" transparency, as described in detail in section 8.4.2.
2) by mixing the fill and underlying colour at each pixel to give a continuous transparency change from 0% to 100%. This shall be done in such a way that no appearance of colour or shape change occurs in any SENC feature on the display, at any intermediate transparency value. The underlying SENC information shall remain distinguishable, except when the overlay colour approaches 100%, in which case S-52, section 2.3.2 (b) applies and an indication is required.
7.1.4 Mariners' & Navigation Information Colours
Mariners' transparent area fill and manufacturers' points and lines
SCLBR Used to generate the scalebar.
CHCOR Hand‑entered chart corrections are marked by the colour.
NINFO Mariners' notes of any form (Symbols, Text) are generated using the colour.
Own ship symbol, course over ground and the speed over ground vector are shown in the colour SHIPS.
The past track of the main position sensor and a secondary position sensor are shown in PSTRK and SYTRK.
The planned route uses the colour PLRTE as well as the symbol set for the planned route elements (waypoints, etc.). Any alternate route is shown in APLRT.
7.1.7 User Interface Colours
For ECDIS user interface colours please refer to MSC.191(79) and IEC 62288.
The Vector Symbol Description Language
This section describes the format that is used by the Presentation Library to define point symbols, complex line-styles and fill patterns.
The vector format uses an imaginary "pen" to draw on a “canvas” (an area of the screen). Positions on the canvas are referred to by two-dimensional Cartesian coordinates (x,y). The coordinates are always within the range of 0 to 32767 units. Each unit represents 0.01 mm on screen. The origin of the coordinates (position 0,0) is on the upper left corner of the two-dimensional canvas. Thus x-coordinates extend to the right and y-coordinates extend downwards.
Fig 2. Pivot point, bounding box and symbol coordinates.
The definitions of point symbols, complex line styles and fill patterns are composed of multiple instructions. Vector symbol definitions described by the vector format are defined within the 'PVCT/SVCT/LVCT'-fields (see section 11). The vector format uses the following additional instructions:
; The semicolon separates the instructions from each other. Every instruction shall be terminated by a semicolon.
, The comma separates the parameters of an instruction from each other. If an instruction does not have any parameters no comma is allowed following the instruction.
The SP instruction selects a pen with a certain colour. The parameter is a single letter which identifies a colour token. The colour tokens used are defined in the "Colour Reference"-fields (see section 10.5.4) which map the single letter definition to one of the standard colour tokens. An SP instruction remains in effect until a new pen is selected. Thus, all following instructions are performed using the selected pen colour.
The ST instruction defines the transparency of the colour that is currently selected. The transparency is given in steps of 25% (0-3, see section 7.4.2). The transparency only affects the polygon fill instruction (see FP) while other instructions (AA, CI, EP, PD) produce opaque drawings.
The SW instruction parameter defines the physical pen-tip width in units of 0.3 millimetres. If a single point is defined, (a pen down with no movement followed by a pen up) then a dot would be drawn using the current line width as a diameter or a square using the current width. (standard pixel diameter).
The PU instruction raises the pen and then moves it to the absolute x,y-coordinates. Thus, no line is drawn by the PU instruction.
x-coordinate, y-coordinate [,x,y, ... x,y]
The PD instruction lowers the pen at the current position and then moves it to the absolute x,y-coordinates. Thus a line in the current colour (see SP) and width (see SW) is drawn by the PD instruction.
The CI instruction draws a circle of a specified radius. The radius determines the size of the circle. The current pen position is the centre of the circle. The CI instruction includes an implicit pen down feature. When a CI instruction is used the pen lifts, moves from the centre of the circle to the starting point on the circumference, lowers the pen, draws the circle, then returns with the pen up to the centre of the circle. The circle is drawn using the current pen colour (see SP) and pen width (see PW).
The PM instruction places the command interpreter in polygon definition mode. In this mode you can construct polygons using other instructions (PU, PD and CI). These instructions are stored in the polygon buffer; they are not executed until the polygon is completely defined. In order to draw the polygon it shall be filled with the FP instruction and/or outlined with the EP instruction. To define a polygon move the pen to the desired starting position (see PU or PD). Then execute PM 0 to enter the polygon mode and specify the appropriate instructions to define the shape of the polygon. If you want to define a sub polygon, end the shape with a PM 1 instruction and define the next shape; execute PM 2 to exit the polygon mode. The current pen position before PM 0 is the first point (vertex) of the polygon. The vertices can be defined with the pen up or down (see PU, PD). However, if you intend to outline the polygon with the EP instruction, note that EP will only draw those points that are defined with the pen down. The FP instruction, on the other hand, fills the polygon, regardless of the pen up / down status.
The EP instruction outlines any polygon that has been previously stored in the polygon buffer (see PM). Only vertices that were defined with the pen down are edged. They are edged using the current pen colour (see SP) and pen width (see PW). Upon completion of the EP instruction, the original pen position and status are restored.
The FP instruction fills a polygon that has been previously placed in the polygon buffer (see PM). The polygon is filled using the current pen colour (see SP) and transparency (see ST). Upon completion of the FP instruction, the original pen position and status (pen up/down) are restored.
symbol name, orientation
The SC instruction calls another symbol definition. Orientation specifies whether the called symbol is drawn upright (orientation = 0) or rotated to the direction of the last pen moving instruction (orientation = 1), or rotated at 90 degrees to the tangent of the symbolized edge at the position of the symbol (orientation = 2). The pivot point of the symbol will be placed on the current pen position. Upon completion of the SC instruction, the original pen position and status (pen up/down) are restored.
Note: The Vector drawing language defines how symbols shall look on the ECDIS screen when drawn. The ECDIS manufacturer does not have to replicate the drawing mechanism itself within their ECDIS. The choice of SENC storage and symbol drawing procedures are up to the manufacturer. The only requirement is that the colours and symbols are replicated from the specifications contained within this document to the satisfaction of the manufacturers type approval body.