I hope this isn't too much of a blue sky question on the development of a control network over time:
A local (less than 30 acre) network is being developed, using many redundant measurements with a total station (no GPS). It's then used routinely to practice topo, layout, etc. down the road. Over time it's expected the network would both grow, and "fill in", with more cross ties etc.
So the question is:
Is it better to do LSA at a given point in time with what you've got, then carry those adjusted coordinates forward, combine them with new observations as they're taken, and run LSA again? Or, should ALL the original observations be kept un-adjusted, and run LSA "globally" with all the observations taken, beginning to end?
I've tried to evaluate the difference mathematically, but have failed to come up with the "technically" correct answer, but now am more interested in standard field practice than anything else.
> ... ALL the original observations be kept un-adjusted, and run LSA "globally" with all the observations taken, beginning to end?
That one. Hands down. Slam dunk. No question.
> > ... ALL the original observations be kept un-adjusted, and run LSA "globally" with all the observations taken, beginning to end?
> That one. Hands down. Slam dunk. No question.
For once! A question on this forum that wasn't answered with "it depends":-O
Thanks!:-)
> I hope this isn't too much of a blue sky question on the development of a control network over time:
I've been entertaining the question off and on of what the ultimate purpose of this control network will be and so far the best I've come up with is that you're planning either an amusement park or ski resort of some sort up there. If this is a long-term project, you really ought to think about how to mark control points in a way that will be frost-resistant over a period of years. Mark stability may otherwise turn out to be a larger factor than the measurement uncertainties in the network.
> so far the best I've come up with is that you're planning either an amusement park or ski resort of some sort up there.
Nope. That's my day job. 😉
>If this is a long-term project, you really ought to think about how to mark control points in a way that will be frost-resistant over a period of years. Mark stability may otherwise turn out to be a larger factor than the measurement uncertainties in the network.
I'm encouraged that you think my increasing ability to make accurate measurements and minimize centering errors is rising to the level that I could detect such shifts.
No, when I started this a little more than a year ago, I had no idea it would take so long to come up to speed (not that I had a ton of time to practice...weekends and summer evenings), and certainly never foresaw that I'd become obsessed with seeking out, chasing down, and understanding the source of every .001' error.
In actuality though, last summer I recorded very little "Z" in my field book, so frost heaves weren't even in the mix (unless I drove over them with my Saab's 4.5" clearance air dam).:-O
Your point is well taken though. I look back on asking what to use for ephemeral station marks and ended up with feathers on 7" deck ledger screws pounded in the dirt. They're still there, but you can move them .03' just looking at them.:-/
I'm not prepared to buy a bunch of those fancy ($30-$50)stainless coaxial monuments with the splaying lower end; But maybe I'll move to longer spikes.
Or move to Texas, where frost is not an issue.:-D