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SwRI can revise these Terms at any time * without notice by updating this posting. * * Trademarks * * The SwRI logo is a trademark of SwRI in the United States and other countries. * */ #ident "@(#) pix_back.c 1.20 05/08/19 SwRI" #include "libtrec_idfs.h" /******************************************************************************* * * * IR_PIXEL_BACKWARD SUBROUTINE * * * * DESCRIPTION * * This routine is called to determine the pixel location associated with * * the time value currently being processed. The current time value has * * been found to be less than the base time; therefore, the time is decreasing* * with respect to the base time. This routine will determine the pixel * * location and a fractional value that indicates the percentage of time * * associated with that pixel for the current time. If the current time is * * found to fall exactly on a pixel boundary, the measurement of the fraction * * depends upon whether the pixel boundary is associated with the "leading * * edge" or "trailing edge". * * * * INPUT VARIABLES * * SDDAS_LONG new_sec seconds component of the current time * * SDDAS_LONG new_nano nanoseconds component of the current time * * SDDAS_LONG *cnt_sub the number of delta T's between the base * * time and the current time * * SDDAS_FLOAT *frac the fractional part of the pixel covered by * * the current time value * * SDDAS_CHAR leading_edge flag indicating if pixel boundary is to be * * treated as a leading or trailing edge: * * 0 - trailing edge * * 1 - leading edge * * SDDAS_SHORT index index to get to the timing structure for * * the sensor being processed * * * * USAGE * * ir_pixel_backward (new_sec, new_nano, &frac, leading_edge, &cnt_sub, * * index) * * * * NECESSARY SUBPROGRAMS * * ir_extra_days () determines the number of extra days to * * be accounted for due to leap years * * adjust_time () corrects time elements if too many seconds * * (day crossing) or too many days (year * * crossing) * * * * EXTERNAL VARIABLES * * struct general_info structure holding information concerning * * ginfo the experiment that is being processed * * * * INTERNAL VARIABLES * * struct experiment_info a pointer to the structure that holds * * *ex specific experiment information * * struct timing *tptr a pointer to the structure that holds timing* * information * * register SDDAS_LONG *l1 pointer to elements in the timing structure * * SDDAS_FLOAT combo_diff the fractional amount of time converted to * * a common time base (seconds) * * SDDAS_LONG pix_inc_sec the time per pixel seconds component * * SDDAS_LONG pix_inc_nsec the time per pixel nanoseconds component * * SDDAS_LONG b_sec, b_nsec the time of the leading edge of the pixel * * SDDAS_LONG add_bsec year and dayofyear time differential to add * * to seconds comparision * * SDDAS_LONG new_bsec, day boundary adjusted start time * * new_bnsec * * SDDAS_SHORT extra_days no. of leap year days (day 366) found * * between start time of pixel and base * * reference time * * SDDAS_SHORT b_yr, b_day the time of the leading edge of the pixel * * SDDAS_SHORT new_yr, day boundary adjusted times * * new_day * * * * SUBSYSTEM * * Display Level * * * ******************************************************************************/ void ir_pixel_backward (SDDAS_LONG new_sec, SDDAS_LONG new_nano, SDDAS_FLOAT *frac, SDDAS_CHAR leading_edge, SDDAS_LONG *cnt_sub, SDDAS_SHORT index) { extern struct general_info ginfo; struct experiment_info *ex; struct timing *tptr; register SDDAS_LONG *l1; SDDAS_FLOAT combo_diff; SDDAS_LONG pix_inc_sec, pix_inc_nsec, b_sec, b_nsec, add_bsec; SDDAS_LONG new_bsec, new_bnsec; SDDAS_SHORT extra_days, b_yr, b_day, new_yr, new_day; /*********************************************************************/ /* Initialize variables. */ /*********************************************************************/ ex = ginfo.expt; *cnt_sub = 0; /*********************************************************************/ /* Update pointer to timing for the leading edge of current pixel. */ /*********************************************************************/ tptr = ex->timing_ptr + index; l1 = &tptr->pix_num; pix_inc_sec = ex->time_values.res_sec; pix_inc_nsec = ex->time_values.res_nano; /*********************************************************************/ /* Since the resolution per pixel could cause a roll-over to the */ /* next day, the start second and nanosecond could be less than the */ /* comparison time; therefore, update the start time. */ /*********************************************************************/ b_yr = tptr->start_yr; b_day = tptr->start_day; b_sec = *(l1 + 1); b_nsec = *(l1 + 2); extra_days = ir_extra_days (tptr->start_yr, ex->time_values.base_year); add_bsec = (tptr->start_yr - ex->time_values.base_year) * 31536000 + (tptr->start_day - ex->time_values.base_day) * 86400 + extra_days * 86400; b_sec += add_bsec; /************************************************************************/ /* In order to avoid round off values, division is avoided to determine */ /* the number of delta T's contained within the differential of the */ /* base and current time. In the end, diff_sec and diff_nano are used */ /* to determine the fractional part of the pixel associated with the */ /* time value. */ /************************************************************************/ if (!(b_sec == new_sec && b_nsec == new_nano)) { while (new_sec < b_sec || (new_sec == b_sec && new_nano < b_nsec)) { ++*cnt_sub; b_sec -= pix_inc_sec; b_nsec -= pix_inc_nsec; if (b_nsec < 0) { --b_sec; b_nsec += 1000000000; } } } /************************************************************************/ /* The time value corresponds exactly to a pixel boundary. The pixel */ /* location and fractional value depend upon whether the pixel is a */ /* leading edge or trailing edge pixel. The pixel locations are */ /* associated with the leading edge of the pixel. */ /************************************************************************/ if (b_sec == new_sec && b_nsec == new_nano) { if (!leading_edge) { *l1 -= *cnt_sub + 1; /******************************************************************/ /* Determine time of the pixel & adjust nanoseconds if necessary. */ /* If the amount of nanoseconds goes negative, 1 seconds worth */ /* of nanoseconds must be borrowed. */ /******************************************************************/ new_day = b_day; new_yr = b_yr; new_bsec = b_sec - add_bsec; new_bnsec = b_nsec; adjust_time (&new_yr, &new_day, &new_bsec, 1); tptr->end_yr = new_yr; tptr->end_day = new_day; *(l1 + 3) = new_bsec; *(l1 + 4) = new_bnsec; /******************************************************************/ /* Determine time of the pixel & adjust nanoseconds if necessary. */ /* If the amount of nanoseconds goes negative, 1 seconds worth */ /* of nanoseconds must be borrowed. */ /******************************************************************/ new_day = b_day; new_yr = b_yr; new_bsec = b_sec - add_bsec - pix_inc_sec; new_bnsec = b_nsec - pix_inc_nsec; if (new_bnsec < 0) { --new_bsec; new_bnsec += 1000000000; } adjust_time (&new_yr, &new_day, &new_bsec, 1); tptr->start_yr = new_yr; tptr->start_day = new_day; *(l1 + 1) = new_bsec; *(l1 + 2) = new_bnsec; } else { *l1 -= *cnt_sub; new_day = b_day; new_yr = b_yr; new_bsec = b_sec - add_bsec; new_bnsec = b_nsec; adjust_time (&new_yr, &new_day, &new_bsec, 1); tptr->start_yr = new_yr; tptr->start_day = new_day; *(l1 + 1) = new_bsec; *(l1 + 2) = new_bnsec; /******************************************************************/ /* Determine time of the pixel & adjust nanoseconds if necessary. */ /* If the amount of nanoseconds goes over 1 second, 1 second worth*/ /* of nanoseconds must be subtracted. */ /******************************************************************/ new_day = b_day; new_yr = b_yr; new_bsec = b_sec - add_bsec + pix_inc_sec; new_bnsec = b_nsec + pix_inc_nsec; if (new_bnsec >= 1000000000) { ++new_bsec; new_bnsec -= 1000000000; } adjust_time (&new_yr, &new_day, &new_bsec, 1); tptr->end_yr = new_yr; tptr->end_day = new_day; *(l1 + 3) = new_bsec; *(l1 + 4) = new_bnsec; } *frac = (leading_edge) ? 0.0 : 1.0; } /**********************************************************************/ /* The time value falls between pixel boundaries. */ /**********************************************************************/ else { *l1 -= *cnt_sub; new_day = b_day; new_yr = b_yr; new_bsec = b_sec - add_bsec; new_bnsec = b_nsec; adjust_time (&new_yr, &new_day, &new_bsec, 1); tptr->start_yr = new_yr; tptr->start_day = new_day; *(l1 + 1) = new_bsec; *(l1 + 2) = new_bnsec; /******************************************************************/ /* Determine time of the pixel & adjust nanoseconds if necessary. */ /* If the amount of nanoseconds goes over 1 second, 1 second worth*/ /* of nanoseconds must be subtracted. */ /******************************************************************/ new_day = b_day; new_yr = b_yr; new_bsec = b_sec - add_bsec + pix_inc_sec; new_bnsec = b_nsec + pix_inc_nsec; if (new_bnsec >= 1000000000) { ++new_bsec; new_bnsec -= 1000000000; } adjust_time (&new_yr, &new_day, &new_bsec, 1); tptr->end_yr = new_yr; tptr->end_day = new_day; *(l1 + 3) = new_bsec; *(l1 + 4) = new_bnsec; /******************************************************************/ /* I believe that the subtraction should be based upon the newly */ /* updated start time, which takes into account the year and day */ /* time differential from the base time. */ /******************************************************************/ combo_diff = (new_sec - b_sec) + 0.000000001 * (new_nano - b_nsec); *frac = combo_diff / ex->time_values.pix_width; } }