FGRAB action: observe and return an image

This page is part of the ING document INS-DAS-24: client-server interface for control of cameras.

Purpose: make one observation and return the resulting image directly to the client.

Actors: Autoguider client; camera server.

Outline: the FGRAB action is invoked. The client receives the image resulting from FGRAB as a returned argument of the action.

Normal course of events:

Client invokes the FGRAB action on the server with these arguments:

Argument1: integration time in seconds.
Argument2: "CLEAR | NOCLEAR" - string to indicate whether a pre-integration clear is required.

Server validates the arguments.
Server clears the detectors if the "CLEAR" parameter is passed, as in the CLEAR action (q.v.).
Server exposes the detectors for the given time, as in the INTEGRATE action (q.v.).
Server reads out the detectors, as in the READOUT action (q.v.).
Server reassembles the regions of the readout into a single rectangle.
Server returns good status for the action, with the image sent back in the action's argument list.

Variations:

At the time of the action, the camera-server is on-line but has an problem outstanding from the initialisation. Server abandons the normal sequence and does this:

Writes an error message directly to the log.
Returns status UDAS__NEEDSRESET to the client.

In step 2, the integration time is negative. Server abandons the normal sequence and does this:

Returns an error message to the client.
Returns status UDAS__BADEXPTIME to the client.

In step 3, 4 or 5, the operations on the camera fail. Server abandons the normal sequence and does this:

Returns an error message to the client.
Returns one of these stati to the client: CAMCMDFAIL, ROFAILED, CAMLINKDOWN.