We are going to do a HIGH ACCURACY Survey, and adjust it with Star Net. What is a realistic centering error to use? Some of our work will be from pillars but we will have to use tripods some and will use forced centering, leap frog, on all instrument stations. We will keep sight distances under 400 feet except two sets of observations from two pillars about 1,200' south of the line of marks we are going to locate. The points that we are locating are on 2 parrallel East West lines about 115' apart. We will be using a LEICA TCRP 1201+ R1000 with temp and pressure corrections. I most likely will upgrade the instrument stations to pillars or permanent brackets in the future. We repete this survey every 2 years.
Steve Corley, post: 379919, member: 23 wrote: We are going to do a HIGH ACCURACY Survey, and adjust it with Star Net. What is a realistic centering error to use? Some of our work will be from pillars but we will have to use tripods some and will use forced centering, leap frog, on all instrument stations. We will keep sight distances under 400 feet except two sets of observations from two pillars about 1,200' south of the line of marks we are going to locate. The points that we are locating are on 2 parrallel East West lines about 115' apart. We will be using a LEICA TCRP 1201+ R1000 with temp and pressure corrections. I most likely will upgrade the instrument stations to pillars or permanent brackets in the future. We repete this survey every 2 years.
Well, horizontal centering doesn't really enter into things if the BS target, instrument, and FS target are centered by forced centering on the identical tribrach or pillar. So the standard error of centering would be 0 under those circumstances. On the other hand, if the targets aren't exactly aligned with the center of the carrier, that would be different. I'm assuming that they are.
Considering that a tribrach with a rotatable plummet set up over a distinct ground mark like a punch mark will have a standard error of horizontal centering of about 0.25mm under normal circumstances, you could always use that value as an upper bound, expecting the actual value to be a bit less.
What Kent said.
FWIW, I use 0.003 centering error for tribrach centered things, 0.005 for rod targets, and 0.01 for vertical measures as a starting point and usually end up there as well. But I don't often set up on concrete pillars.