Perform a scan relative to the current telescope position.

Mandatory arguments:

ScanFile file

The file whose contents describe the trajectory of the scan.

Optional Arguments:

Count repeat

The number of times to repeat the body of the scan. If this is not supplied, the body of the scan is performed a single time.

ScanScale scale

The amount by which to scale the amplitude of the scan. This must be no more than one.

Example:

The following command would perform the scan performed in the file myscan.scn, repeating the body of this scan ten times, with half the amplitude described in the file.

  scan myscan.scn, repeat=10, scale=0.5

Context:

Scans consist of three phases, a startup acceleration phase, followed by a repeating part, and finishing with an ending deceleration phase. The starting and ending positions, velocities and accelerations of each cycle of the body of the scan, are required to be the same, and thus each cycle consists of a back and forth motion.

The format of scan-files:

The following is an example of the contents of a scan file.

# Duration        Azimuth      Elevation      Deck Angle
#   (s)         p    v    a     p  v  a        p  v  a

START:          0   0.0 -4.0    0  0  0        0  0  0
    5         -20   0.0  4.0    0  0  0        0  0  0
    5           0   0.0 -4.0    0  0  0        0  0  0

The first two lines are examples of arbitrary comments, and the third an arbitrary blank line. Comments can be written at the end of any line, provided that they are preceded by a # character.

The line that is started with the word START:, must always be the first line in the file that is neither a comment-line nor a blank line. The six numbers that follow it indicate the azimuth, elevation and deck-angle positions, velocities and accelerations at which the repeating body of the scan should start. These numbers have units of degrees, degrees/s and degrees/s^2, respectively. The positions are relative to the axis positions that the telescope had before the scan was started, whereas the velocities and accelerations are absolute.

The two lines that follow the starting line, each start with a number which specifies the duration of a move in integer seconds. During this time, the azimuth, elevation and deck axes are are to be moved smoothly to the positions, velocities and accelerations indicated by the remaining 6 numbers on the line. Note that the positions, velocities and accelerations of the final line, must match those of the starting line, such that the scan can be seamlessly repeated.

The trajectory followed is the cubic interpolation between the positions, velocities and accelerations of successive lines. If the above file is given the name myscan.png, and is executed as follows, using the scan command:

 scan myscan.scn, repeat=3

Then the result is the following trajectory in azimuth, in which the body of the scan is repeated 3 times. Since the positions, velocities and accelerations specified above for the elevation and deck axes are zero, these axes don't move.