current direction is identical to direction on the screen. For other map projections, the portrayed direction must be computed. Figure 9.3 Portrayal of the direction, based on the current direction. The dashed line is the – arrow’s centerline, and the origin of the East-North axis is at the pivot point. arrow’s arrow’s True north has a direction of 0 degrees. 9.2.3 Arrow Colour and Speed Bands The colour of the arrow must be based on the speed value of the data, and must have 9 bands corresponding to the speed ranges (Table 9.1). The range of speeds (Table 9.1) was selected to (a) emphasize differences at low speeds (0.0 to 3 kn), and (b) be capable of displaying large currents (13 kn and above). NOTE: The largest tidal currents may be those in the strait near Saltstrumen, Norway, which reach 22 kn. Table 9.1 Speed ranges (knots) for the 9-band display. – Speed Minimum Maximum Appx. Band Speed (kn) Speed (kn) Interval (kn) 1 0.00 0.49 0.5 2 0.50 0.99 0.5 3 1.00 1.99 1 4 2.00 2.99 1 5 3.00 4.99 2 6 5.00 6.99 2 7 7.00 9.99 3 8 10.00 12.99 3 9 13.00 99.99 87 Colours are associated with each speed band, and must be distinguishable in the three viewing environments: day, dusk, and night. Color values for day conditions are shown in Table 9.2. Colours for dusk and night conditions are given in ANNEX H COLOUR TABLES. (The – monitor gamma values need to be taken into account refer to IHO standards). – Table 9.2 Colour schema for day conditions. –
current direction is identical to direction on the screen. For other map projections, the portrayed direction must be computed. Figure 9.3 – Portrayal of the arrow’s direction, based on the current direction. The dashed line is the arrow’s centerline, and the origin of the East-North axis is at the arrow’s pivot point. True north has a direction of 0 degrees. 9.2.3 Arrow Colour and Speed Bands The colour of the arrow must be based on the speed value of the data, and must have 9 bands corresponding to the speed ranges (Table 9.1). The range of speeds (Table 9.1) was selected to (a) emphasize differences at low speeds (0.0 to 3 kn), and (b) be capable of displaying large currents (13 kn and above). NOTE: The largest tidal currents may be those in the strait near Saltstrumen, Norway, which reach 22 kn. Table 9.1 – Speed ranges (knots) for the 9-band display. Speed Band Minimum Speed (kn) Maximum Speed (kn) Appx. Interval (kn) 1 0.00 0.49 0.5 2 0.50 0.99 0.5 3 1.00 1.99 1 4 2.00 2.99 1 5 3.00 4.99 2 6 5.00 6.99 2 7 7.00 9.99 3 8 10.00 12.99 3 9 13.00 99.99 87 Colours are associated with each speed band, and must be distinguishable in the three viewing environments: day, dusk, and night. Color values for day conditions are shown in Table 9.2. Colours for dusk and night conditions are given in ANNEX H – COLOUR TABLES. (The monitor gamma values need to be taken into account – refer to IHO standards). Table 9.2 – Colour schema for day conditions.
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