The default location of the input file for custom dither patterns is “/data1/nirim” on the computer sand. This may be changed to any location that the program has permission to write files. To change the locations of the file simply type the new path including the name of the file in the Offset File field. This field assumes that the entire “absolute” path is included with the file name and does not account for relative pathnames.
The format of the file is one offset per line with both RA and DEC offsets separated by a comma. The offsets are assumed to be in arcseconds. The offsets in the file are relative. The telescope is moved from 0,0 by the amount of the first offset, then from the position of the first offset by the amount of the second offset, etc. The offsets in the file are NOT all referenced to the 0,0 position. An example offset file would look like:
0 , 300
0 ,
-300
0 ,
0
0 ,
-300
10 ,
0
0 ,
320
0 ,
0
0 ,
300
-20 ,
0
0 ,
-300
0 ,
0
0 ,
-300
20 ,
0
0 ,
260
0 ,
0
0 ,
300
-20 ,
0
This offset file would offset first north, then back to the starting position, a second exposure at the center, then south, then east, then north again, etc. Plus signs on positive offsets are optional; the number of spaces before or after offset amounts is also optional.
The read button tells the program to open and read the file whose name is given in the Offset File field. If the Forward or Back buttons are clicked on before a file is read an error will occur. Once the file is read the Read File button must be used again before a new custom offset pattern is used.
The number of coadds is set by default to be 1. Any number <1 will be ignored and the default setting of 1 will be used. If the number of coadds is 1 then each click of the Forward button will send a command to the TCS to move the telescope to the next position in the offsets file. If the number of coadds is >1 then the Forward button will increment a counter within the program without sending a command to the TCS. It will also send a message to the console from which the GUI was started and write a message to the logfile. This allows the observer to make multiple observations at the same position without having to keep track of how many coadds have been done. As long as the Forward button is clicked before each observation, the telescope will be offset to the next position at the correct time.
The Forward and Back buttons are used to offset the telescope either one “position” forward in the observing sequence (this may mean incrementing the coadds counter) or one position back. The Back button does not take into account the number of coadds that have been done at any observing position and resets the coadds counter to 0.
N.B. BE VERY CAUTIOUS ABOUT USING THE BACK BUTTON WHEN
YOU ARE DOING COADDS! It may be
confusing if one makes an error when using 2 or more coadds. If one clicks on
the Forward button twice, before the last coadd at a particular
position, the TCS would be sent a command to offset to the next position in the
grid. If the Back button is then clicked the telescope will be offset
back, but the next click of the Forward button will not offset the
telescope it will simply increment the number of coadds.
The Home button reverses all of the offsets done by the program itself. However, this does not set the telescope offsets to 0”,0” if the telescope has been offset using some other method (for instance the operator has input an offset).