# Choosing ‘best’ coordinates of base station based on multiple days of surveying

I’m new to surveying and have just been doing some GPS work as part of a larger project. So I have very basic questions about finding the ‘known’ location for a base station. I’ve gone out and surveyed (RTK) at this one location three different days in the last two weeks. I’m walking with a Trimble backpack to survey a large area of beach, with my base station set up on a fixed-height tripod in the same location each day. The occupation times at my base station were just over 2 hours for day 1, just over 5 hours for day 2, and just under 4 hours for day 3. I’ve submitted the base station data for each day to OPUS (my OPUS reports were generated, respectively, 9 days, 2 days, and 1 day after each survey).

I’ve now got three slightly different coordinates for the base station, and I’m wondering which one to ‘choose’ as the ‘real’ base location to adjust all my data (so the three days worth of data line up) and use for future surveying at this site. According to the OPUS reports, horizontal coordinates are all within 22mm of each other. Errors are all less than 0.05m. Ambiguities are all above 85% and RMS is around 0.012. For the two longer occupations, the percent observations used is around 88% (for the shorter occupation, it’s about 96%).

Do I just choose the longest occupation? Is there a way to combine the three different results to find the best solution? Should I resubmit the long occupation in a few days to OPUS to get a better solution (maybe get percent observations used above 90%) and then use that or will it not make much of a difference after a day?

Any guidance is appreciated!

Log in to reply.