ssecorr -- Correct errors in FGS star selector encoder data.
ssecorr infile inmask ssetable threshold
There are two types of star selector encoder data--raw encoder data and 24-bit averaged data. Raw encoder data is in groups SSENCA and SSENCB. 24-bit averaged data is in groups SSAVGA and SSAVGB.
When raw encoder data is being corrected, the right-most, i.e., least significant, 7 bits (0-6) of the 4-byte integer reading are used as the error table index to look up the correction for an encoder position. Numbers stored in the error table will be 1024 times larger than the actual errors, therefore, input readings are multiplied by 1024 before errors are subtracted.
When the astrometry mode is set to FINELOCK, 24-bit averaged data is produced, which is 8 times larger than original readings, and bits 3-9 are used as the error table index (not 0-6). Input readings are multiplied by 128 before errors are subtracted.
With either type of data, the final results are 1024 times larger than the original reading.
After corrections are made to the encoder data, the keyword CALECDR is set to true, preventing the data from being corrected a second time. The CALECDR flag is checked before ssecorr runs; no corrections will be made if its value is true.
1. Correct the star selector encoder error for input files yssecorr$infile.d1h, and yssecorr$infile.d2h with corresponding mask files xssecorr$inmask.m1h, xssecorr$inmask.m2h. Produce the error table xssecorr$fgsencdr.tab and reject points with mask values below 0.5:
fg> ssecorr (infile = "yssecorr$infile.d![1-2]h", \ >>> inmask = "xssecorr$inmask.m![1-2]h", ssetable = "xssecorr$fgsencdr",\ >>> threshold = 0.5)