stella.util
Class TelescopeError

java.lang.Object
  stella.util.TelescopeError

All Implemented Interfaces:

Multidimensional

public class TelescopeError
extends Object
implements Multidimensional

A class that models a time-dependend shift according to an overlay of sine functions. A PID is then used to correct for this shift, and as a test, the difference between the PID response and the true function is feed into the PID. For optimal performance, the frequencies should be plain integers.
To allow optimization of the PID with a simplex algorithm, this class also implements the Multidimensional interface that returns a measure of the goodness-of-leveling of the PID.

Nested Class Summary

static class

TelescopeError.Parse A command-line frontend to the sine-error class.

Field Summary

static int	ABSOLUTESUM The indicator for absoulte error-sum quality measure.
private double[]	amplitude The coefficients of the input function, amplitude.
private double	deadtime The deadtime until the system starts reacting, in seconds.
private double	diameter The diameter of the guiding telescope in meters.
private double	expose The exposure time on the guiding unit in sec.
private static double	IMPOSSIBLE If the PID returns a correction higher then this, we cannot follow.
private double	jerk The jerk of the axis, in deg/s^3
private static double[]	motion For optimizing runs, we use the same random image motion.
private double	noise The coefficient for thw gaussian noise.
private static double	OVERREACT If the PID starts to oscilate, the correction will be higher as.
private double[]	period The coefficients of the input function, period.
private double[]	phase The coefficients of the input function, phase.
private PIDControl	pid The PIDController handling the error function.
private double	pidfreq The frequency at which the PID is queried.
private boolean	pionly If true, only optimize PI parameters, keep D fixed.
private int	qualitymeasure The quality measure, 0-3.
private static int	RESOLUTION The number of steps skipped for error determination.
private double	seeing The seeing in arc-sec, if seeing should be included.
static int	SQUARESUM The indicator for error square-sum quality measure.
static int	TABSOLUTESUM The indicator for absolute error times t sum quality measure.
private static double	TINY A small number to prevent division-by-zero in oscillating test.
static int	TSQUARESUM The indicator for error squared times t sum quality measure.
private Random	white The random number generator.
private double	wind The wind speed, only if seeing > 0.

Constructor Summary

TelescopeError(double[] a, double[] p, double[] phi)
Constructs a new sine error function specifiying the coefficients of the error function.

TelescopeError(double[] a, double[] p, double[] phi, double random)
Constructs a new sine error function specifiying the coefficients of the error function.

Method Summary

int	dimension() Return three for the three PID parameters.
double	evaluate(VectorG pidvals) Evaluate the PID.
double	getErrorFunction(double t) Calculates the error function at the given time.
double	getMaximumPeriod() Returns the period of the error function after which it repeats itself.
double	runPID(PrintWriter out) Runs an entire loop using the specified PID and the underlying error function.
void	setAxisJerk(double newjerk) Sets the jerk of the motor axis in degs/s^3.
void	setDelay(double newdeadtime) Sets the deadtime time.
void	setGuiderExpose(double newexpose) Sets the guider exposure time.
void	setPID(PIDControl handle) Sets the PIDControler that should level the error function.
void	setPIDFrequency(double f) Sets the PID frequency.
void	setPIOnly(boolean onlypi) Sets the desired optimization strategy.
void	setQualityMeasure(int newqual) Sets the quality measurement.
void	setSeeing(double newseeing) Sets the seeing level.
void	setTelescopeSize(double newsize) Sets the size of the guider telescope.
void	setWindSpeed(double newwind) Sets the wind speed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SQUARESUM

public static final int SQUARESUM

The indicator for error square-sum quality measure.

See Also:

Constant Field Values

ABSOLUTESUM

public static final int ABSOLUTESUM

The indicator for absoulte error-sum quality measure.

See Also:

Constant Field Values

TSQUARESUM

public static final int TSQUARESUM

The indicator for error squared times t sum quality measure.

See Also:

Constant Field Values

TABSOLUTESUM

public static final int TABSOLUTESUM

The indicator for absolute error times t sum quality measure.

See Also:

Constant Field Values

amplitude

private double[] amplitude

The coefficients of the input function, amplitude.

period

private double[] period

The coefficients of the input function, period.

phase

private double[] phase

The coefficients of the input function, phase.

noise

private double noise

The coefficient for thw gaussian noise.

white

private Random white

The random number generator.

pid

private PIDControl pid

The PIDController handling the error function.

pidfreq

private double pidfreq

The frequency at which the PID is queried.

deadtime

private double deadtime

The deadtime until the system starts reacting, in seconds.

jerk

private double jerk

The jerk of the axis, in deg/s^3

seeing

private double seeing

The seeing in arc-sec, if seeing should be included.

wind

private double wind

The wind speed, only if seeing > 0.

diameter

private double diameter

The diameter of the guiding telescope in meters. Only if seeing > 0.

expose

private double expose

The exposure time on the guiding unit in sec. Only if seeing > 0.

motion

private static double[] motion

For optimizing runs, we use the same random image motion.

qualitymeasure

private int qualitymeasure

The quality measure, 0-3.

pionly

private boolean pionly

If true, only optimize PI parameters, keep D fixed.

RESOLUTION

private static final int RESOLUTION

The number of steps skipped for error determination.

See Also:

Constant Field Values

OVERREACT

private static final double OVERREACT

If the PID starts to oscilate, the correction will be higher as.

See Also:

Constant Field Values

IMPOSSIBLE

private static final double IMPOSSIBLE

If the PID returns a correction higher then this, we cannot follow.

See Also:

Constant Field Values

TINY

private static final double TINY

A small number to prevent division-by-zero in oscillating test.

See Also:

Constant Field Values

Constructor Detail

TelescopeError

public TelescopeError(double[] a,
                      double[] p,
                      double[] phi)

Constructs a new sine error function specifiying the coefficients of the error function. No white noise.

TelescopeError

public TelescopeError(double[] a,
                      double[] p,
                      double[] phi,
                      double random)

Constructs a new sine error function specifiying the coefficients of the error function. White noise is added.

Method Detail

setPID

public void setPID(PIDControl handle)

Sets the PIDControler that should level the error function.

setPIDFrequency

public void setPIDFrequency(double f)

Sets the PID frequency.

setQualityMeasure

public void setQualityMeasure(int newqual)

Sets the quality measurement. Defines how the quality of the PID is measured. The values allowed are:

• SQUARESUM:
• ABSOLUTESUM:
• TSQUARESUM:
• TABSOLUTESUM:

All of the quality measurements are obtained only after the intial transient response, defined by the number of steps given in #RESPONSE.

setDelay

public void setDelay(double newdeadtime)

Sets the deadtime time. This is the time it takes the system to start reacting to a new signal. The time unit is the inverse of the PID frequency.

setAxisJerk

public void setAxisJerk(double newjerk)

Sets the jerk of the motor axis in degs/s^3.

setPIOnly

public void setPIOnly(boolean onlypi)

Sets the desired optimization strategy. If true, only P and I are changed.

setSeeing

public void setSeeing(double newseeing)

Sets the seeing level.

setWindSpeed

public void setWindSpeed(double newwind)

Sets the wind speed. Necessary if seeing is included.

setGuiderExpose

public void setGuiderExpose(double newexpose)

Sets the guider exposure time. Necessary if seeing is included.

setTelescopeSize

public void setTelescopeSize(double newsize)

Sets the size of the guider telescope. Necessary if seeing is included.

getErrorFunction

public double getErrorFunction(double t)

Calculates the error function at the given time. The function is evaluated as

       f = Σiaiċsin(2πfi*t+φi
       

If additional white-nois of the error-function (not seeing!) is requested, it is added to the error function right here.

getMaximumPeriod

public double getMaximumPeriod()

Returns the period of the error function after which it repeats itself. The number of steps of the simulation is this over the pid-frequency.

runPID

public double runPID(PrintWriter out)

Runs an entire loop using the specified PID and the underlying error function. If the PrintWriter supplied is not null, the result of each step are writtn within, the procedure is as follows.

• We start at time t=0 and increase the time in steps returned by #getTimeStep until we reach t >= 1.
• We start at t=0 calculating the error function and plugging it into the PID with #addError.
• At any time ti>0, we retrieve the PID response with #getCorrection and feed the difference of the error function and the correction into the PID as the new error.
• At any step, the absolute value of the difference between the error function and the PID is calculated and added to the offset.
• At t=1, the offset is returned.

dimension

public int dimension()

Return three for the three PID parameters.

Specified by:

dimension in interface Multidimensional

evaluate

public double evaluate(VectorG pidvals)

Evaluate the PID. This runs the PID and returns the offset. This offset, in turn, should be minimized. The parameters in the vector argument are interpreted as the proportional, integral, and differential parameter of the PID, in this order.

Specified by:

evaluate in interface Multidimensional