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next planned revision: 2009-11 |
These definitions help understand the scripts.
The coordinate axis are those of general mathematics, i.e. the abscissa axis x points to the right and the ordinate axis y points up.
Angles are in radians, they start at the x-axis and increase counterclockwise.
Angles are also called "azimuths" because geometers use this term when surveying the actual accelerators that are lying horizontally in a landscape.
There are two predefined beam pipe rings, an inner ring and an outer ring, as shown in pale yellow in the figure.
The axes have their origin in the centre of the rings. The total plane angle of 2π is divided into a number of equal sectors, where the number of sectors must be a multiple of 8.
Sectors define a set of azimuths. The angle of a sector is called the azimuth step.
The azimuths of a sector are symmetrically laid out on both sides of the sector's own azimuth. In the image the green sector has azimuth 0 and it therefore covers some azimuths above and below the x-axis.
To avoid problems with signs, all angles are reduced to values between 0 and 2π.
The constant cNrSectors is given, but cAzimuthStep is set by the startup handler and should be considered a constant (the fact that it must be computed precludes defining it as a constant in the current implementation of Revolution.)
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