Imaging program has INIT/GOS command. Point at a bright star before issuing command. INIT moves star around in 3x3 grid by fixed amount on sky (50 pixels, but can specify with INIT argument), finds centroid, and gets linear transformation solution; it loads this in internal varaibles. In addition to this, instrument block needs location of instrument relative to rotator center. To do this, determine offset in RA/DEC to move star from rotator center to center of instrument while at PA=0. Then INSTBLOCK dra ddec command will send proper SETINST command to tocc to set instrument block, using the offset and the transformation information.
At a lower level: SETINST inst sx sy dra -ddec rot, where rot is in degrees.
For instrument at NA2 (no rotator), need to add extra arguments: rot0 fixed, where rot0 should be the negative of the derived rotation, and fixed should be 1 to identify a fixed instrument.
The instrument blocks show up at the end of the sysscf file.