FRAME OF REFERENCE

Chapter 3 Combat Systems Alignment (gun/battery)

Fire Controlman Volume 04-Fire Control Maintenance Concepts
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method for determining the position of a point, a line, a curve, or a plane in a space of given dimensions, called a reference frame. Figure 3-1 shows typical ex- amples of parallel lines and planes. Figure 3-1.—Typical examples of parallel lines and planes. Ultimately, the alignment of parallel lines, parallel planes, and coordinate systems is used to establish a pointing line for each piece of equipment in the ship’s combat system. The line representing the direction in which apiece of equipment is pointing is the pointing line of that equipment. As previously indicated, the pointing line may be the bore axis of a gun, the line of sight of a director, or the propagation axis of a radar beam. Accurate alignment is not possible unless the pointing line is precisely determined. FRAME OF REFERENCE The reference point, the reference direction, and the reference plane form a geometric structure called the reference plane. In the complete reference frame, directions are specified by two angles (train and ele- vation), measured about the reference point. Figure 3-2 shows the measurement of an angle from a refer- ence direction. Figure 3-2.—Measurement of an angle from a reference direction. A geometric measurement is based on a definite and complete set of geometric references. To permit clear and accurate definition of target position, a definite point on the ship (such as a director) is selected as the starting point for the measurement. As a reference point, a director center of rotation is selected arbitrarily because the director has interface with all the major equipment of a battery. Once the reference point is determined, it becomes apart of any future measurement made from it and must be clearly specified before subsequent measurements have any meaning. Once the reference point is selected, a reference direction is established from which train angles are measured. Train angles are measured about the refer- ence point, beginning at the reference direction. In naval combat systems, the ship’s centerline, which points in the direction of the bow, is used as the refer- ence direction. Angles expressing direction cannot be described unless a means is available for specifying the plane in 3-2

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