tcc.axis.computeSlew Namespace Reference

Classes
class	SlewData
	Data about a slew. More...
class	FullSlewData
	Contains full data about one slew iteration. More...

Functions
def	computeSlew
	Compute a slew to a given user-specified position, by iteration. More...

Variables
float	ShortSlewTime = 5.0
tuple	_ValidStartingStateSet

Function Documentation

def tcc.axis.computeSlew.computeSlew	(		minEndTime,
			obj,
			earth,
			inst,
			telMod,
			axeLim,
			tune
	)

Compute a slew to a given user-specified position, by iteration.

Before calling this:

• Update obj at some time near "now" including applying doRestart and wrap preferences.
• Send the DRIFT command to all axes that are moving (whether you want to halt them or slew them) and update obj.actMount and obj.axisCmdState accordingly.

This routine then does the following for each axis:

• If obj.axisCmdState==AxisState_Drifting and obj.targetMount[axis].isfinite(): compute a slew to the new position. Raise an exception if such a slew cannot be computed.
• If obj.axisCmdState==AxisState_Drifting and not obj.targetMount.isfinite(): try to compute a slew to a halt. If that fails, set SlewData.pathList[axis]=(); the caller then must command that axis to halt!
• For other axes, leave the axis alone.

Parameters

[in,out]	obj	object block: input: object block computed at approximately the current time (see above) output: the object block is be recomputed obj.targetMount is set to the final pvt for each axis that is slewing or halting; it is unchanged for axes that are already halted obj.axisCmdState is set to AxisState_Halting or AxisState_Slewing for axes that are drifting obj.axisErrCode is updated appropriately for axes that are drifting obj.slewEndTime is set
[in]	minEndTime	earliest date at which slew may finish (TAI, MJD sec)
[in]	earth	earth orientation data, a tcc.base.Earth
[in]	inst	instrument-position information block, a tcc.base.Inst
[in]	telMod	telescope model, a tcc.base.TelMod
[in]	axeLim	axes limits block, a tcc.base.AxeLim
[in]	tune	axes motion tuning constants block, a tc.base.Tune

Returns

slewData: a SlewData

Exceptions

RuntimeError

if any of the following are true: obj.axisCmdState is not one of AxisState_NotAvailable, AxisState_Halted, or AxisState_Drifting for any axis obj.actMount is not finite for any axis whose axisCmdState = AxisState_Drifting a valid slew cannot be computed for an axis being slewed (not halted)

Warning

• If an axis is to be halted, and a valid slew cannot be computed, then slewData.pathList[axis] = (). The caller must stop the axis!

Special cases:

• If no axes are to be slewed, pathList[axis] will be an empty list for all axes, but begTime and endTime will be correct – set as for the shortest possible slew.

Details: The slew path is computed by iteration, as follows:

• The end time of the slew is estimated (based on many factors, see code)
• the target mount coordinates (p,v,t) are computed at that instant
• A slew is computed which meets the target path (using linear extrapolation); this also gives us the true end time
• The estimated and true end times are compared; if they are too far apart, the cycle is repeated

There are several parameters in the Tune block which control this iteration process. See TuneBlkDef for more info.

Types of motion:

• Slew: move to a requested position via a computed, smooth path. Used for axes with a requested target position.
• Controlled stop: move to the current pos. via a computed, smooth path. Used for axes with no position requested (e.g. coord. sys. = "none").

History: 2013-12-09 ROwen converted from computeSlew.for

Definition at line 72 of file computeSlew.py.

Variable Documentation

tuple tcc.axis.computeSlew._ValidStartingStateSet

Initial value:

= set((
    tcc.base.AxisState_NotAvailable,
    tcc.base.AxisState_Halted,
    tcc.base.AxisState_Drifting,
))

Definition at line 38 of file computeSlew.py.

float tcc.axis.computeSlew.ShortSlewTime = 5.0

Definition at line 14 of file computeSlew.py.