Leginon

h1. Drift Manager

The Drift Manager monitor has two functions. It works with <link

linkend="transmanager_node">Transform Manager</link> to keep the accuracy of targeting

through long experiment and certain operation such as the change of stage z position.

* Monitoring drift when requested

* Declaring that a drift has occured.

The first way of determining that drift is occurring is by measuring it directly. A drift

measurement is initiated in one of two ways:

* The user may manually monitor drift in the DriftManager node. This can be either a

single measurement of the current drift rate or a loop that measures the drift rate until

it falls below a threshold set in the DriftManager settings dialog.

* The Focus node can request drift monitoring in preparation for doing auto focus. If

drifting is in progress, DriftManager enters a measurement loop until drift falls below

the threshold and declares that a drift has occured

Drifting can also be assumed to have occurred without doing a measurement. This is done as

a result of certain operations of Leginon:

* When stage Z position is changed, there is often a side effect of X and Y position

shifting also. Drift is always declared after stage Z correction is made in a focus

sequence.

*  When in queuing mode, it is often desirable to assume that drift has occured whenever

a queue of targets is submitted. This is due to the possible long time durations and large

stage movements. There is an option in each targeting node to "Declare drift when queue

submitted".

* Sometimes targeting accuracy is failing because the image from which the targets were

selected was acquired using a preset with a bad image shift. The targets can be corrected

using the following method: pause the processing of the targets, adjust the image shift of

the bad preset, declare drift in DriftManager, continue processing the targets. The image

shift adjustment will be treated as a drift and the targets will be corrected.

* When various environmental factors have changed that the user thinks have caused a

drift. One example is filling up the liquid nitrogen dewar. In this case, the user must

click the "Declare Drift" button in the DriftManager node.

In the above cases, whether drift is measured or assumed, a drift time stamp is entered

into the database to mark when the drift occured. Acquisition nodes have an option "Adjust

targets for drift" which causes them to look for these drift time stamps before processing a

target and acquiring an image. If a drift occured after the target was created, the target is

declared invalid. To adjust the target, the Acquisition node must send a request to the

DriftManager to measure the total drift that has occurred since the target was created. The

DriftManager will load the target's parent image from the database and reacquire it under its

original imaging conditions as a different version. The correlation shift is then stored in

the database so that any target that came from this image can be adjusted in the same way.

<highlights>

Initiating drift monitoring by a focuser node requires two bindings to do such

task.

<simplelist type="vert">

<member> FocuserNode - (DriftMonitorRequestEvent) -> DriftManagerNode</member>

<member> DriftManagerNode - (DriftMonitorResultEvent) -> FocusNode</member>

</simplelist>

For DriftManager to change presets, two bindings are needed:

<simplelist type="vert">

<member> DriftManagerNode - (ChangePresetEvent) -> PresetsManagerNode</member>

<member> PresetsManagerNode -(PresetChangedEvent) -> DriftManagerNode</member>

</simplelist>

</highlights>

h2.  Settings

*  Wait for drift to be less than "3e-10" m = the distance threshold for drift

checking to stop. A drift above the threshold will cause the Drift Manager to continue

to monitor drift.

*  Wait "2.5" seconds between checking drift = the amount of time paused between

acquisition of images to measure drift. This applies to requests from Focuser nodes,

too.

*  the typical <link linkend="camconfig">Instrument and Camera

Configuration</link>

h2.  Toolbar

*  Measure Drift = stand alone button to quickly and manually assess drift

once.

*  Check Drift = stand alone button to start drift monitoring sequence.

*  Abort = this will abort the Drift Manager drift monitoring sequence.