The NGSGPS week calendar only goes back to year 2006.?ÿ But the ITRS was first realized in 1988 (ITRF88).?ÿ It is my understanding that all the ITRF's are time dependent, but not the NAD83 realizations.?ÿ What is the likely reason NGS does not extend their GPS week calendar further back to 1988??ÿ ?ÿ
all the ITRF's are time dependent, but not the NAD83 realizations
A realization (reference frame), by definition, is time dependent - it is the physical manifestation of a reference system, at a specified epoch. Both ITRF and NAD83 have multiple realizations, as well as estimated velocities which make it possible to transform positions across time for both.
What is the likely reason NGS does not extend their GPS week calendar further back to 1988??ÿ ?ÿ
Probably because there are very few people still processing data from 15 years ago, and practically none who are processing NGS projects i.e., bluebooking from that time period.
For GNSS calendars going back to 1994 see: https://www.gnsscalendar.com/index.html?year=1994
For the code (in C) to create your own tool to perform a variety of date/time conversions, see this page: https://geodesy.noaa.gov/gps-toolbox/bwr-c.txt
"BWR" is Dr. Benjamin W. Remondi.?ÿ
Not sure how the relationship between year-month-day-hour-minute-second and GPS time (defined as GPS week plus seconds of week) relate to use of differences in time used e.g. to transform positional coordinates across time.
A work-around to finding the GPS date for a month-day-year (MDY) of interest is to use the "User Friendly CORS" at: https://geodesy.noaa.gov/UFCORS/ where the user is prompted for the date as either MDY or Year plus day-of-year (DOY).
Note that CORS data is only available from 1 January 1994.?ÿ
HTH,
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