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There was an itty - bitty bridge job - resurface the deck, upgrade the bridge end treatments for guardrail- check for utility conflicts.
The survey request was for 500 feet out from each end of the bridge- so the job is about 1100' long +/-.
It's also adjacent to a project from about 5 years back. So I had my guy go out, set 2 points and hit them both with RTK double ties- 3 minutes observations.
Crewster meaned the numbers and handed it off to the construction crew to complete their little rtk topo.....
crewster came back to the office, dumped it into TBC and meaned the CSF for the 2 points and submitted that as part of the report.
I normally don't check these too closely because we submit it to someone who makes as much a I do to check them, sooo...(yeah- I know bad on my part)
anyway-
TPTB offered several comments.... some (a few) rightly so... anyway the one that chapped me a bit was this one.... about the scale factor...
on an 1100' long project at 3300' elevation......
"The CSF is different on the readme file, IFT file, TBC project and the CSF from CN# ####. If the CSF of 0.999531320 from CN# #### is used the accuracy is greater than 1:480,000." (emphasis mine)
our CSF was Different in the 7th, 8th, and 9th decimal place.....:-/
Rankin_File, post: 327153, member: 101 wrote:
.
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There was an itty - bitty bridge job - resurface the deck, upgrade the bridge end treatments fo0r guardrail- check for utility conflicts.
The survey request was for 500 feet out from each end of the bridge- so the job is about 1100' long +/-.
It's also adjacent to a project rom about 5 years back. So I had my guy go out, set 2 points and hit them both with RTK double ties- 3 minutes observations.
Crewster meaned the numbers and handed it of to the construction crew to complete their little rtk topo.....
crewster came back to the office, dumped it into TBC and meaned the CSF for the 2 points and submitted that as part of the report.
I normally don't check these too closely because we submit it to someone who makes as much a I do to check them, sooo...(yeah- I know bad on my part)
anyway-
TPTB offered several comments.... some a few rightly so... anyway the one that chapped me a bit was this one.... about the scale factor...
on an 1100' long project at 3300' elevation......
"The CSF is different on the readme file, IFT file, TBC project and the CSF from CN# ####. If the CSF of 0.999531320 from CN# #### is used the accuracy is greater than 1:480,000." (emphasis mine)
our CSF was Different in the 7th, 8th, and 9th decimal place.....:-/
I keep tellin' ya - 95% of the folks that require this type of info don't have a clue what it means or what to do with it...
Rankin_File, post: 327153, member: 101 wrote:
.
.
There was an itty - bitty bridge job - resurface the deck, upgrade the bridge end treatments for guardrail- check for utility conflicts.
The survey request was for 500 feet out from each end of the bridge- so the job is about 1100' long +/-.
It's also adjacent to a project from about 5 years back. So I had my guy go out, set 2 points and hit them both with RTK double ties- 3 minutes observations.
Crewster meaned the numbers and handed it off to the construction crew to complete their little rtk topo.....
crewster came back to the office, dumped it into TBC and meaned the CSF for the 2 points and submitted that as part of the report.
I normally don't check these too closely because we submit it to someone who makes as much a I do to check them, sooo...(yeah- I know bad on my part)
anyway-
TPTB offered several comments.... some (a few) rightly so... anyway the one that chapped me a bit was this one.... about the scale factor...
on an 1100' long project at 3300' elevation......
"The CSF is different on the readme file, IFT file, TBC project and the CSF from CN# ####. If the CSF of 0.999531320 from CN# #### is used the accuracy is greater than 1:480,000." (emphasis mine)
our CSF was Different in the 7th, 8th, and 9th decimal place.....:-/
"If the CSF of 0.999531320"
1100',,,,,,,, then every number after the first 3 is inconsequential, unless this is part of a larger project, but knowing DOT's they often want one of those numbers for each little thing..........
Have you ever tried to get them to stop after the sixth place,,,,,,,,, .01' in 10000'?
.999531 isn't a very small CSF for MT.
MightyMoe, post: 327211, member: 700 wrote: "If the CSF of 0.999531320"
1100',,,,,,,, then every number after the first 3 is inconsequential, unless this is part of a larger project, but knowing DOT's they often want one of those numbers for each little thing..........
Have you ever tried to get them to stop after the sixth place,,,,,,,,, .01' in 10000'?
.999531 isn't a very small CSF for MT.
On an 1100 foot project with a 1:10k spec you can use 80% of your error budget stopping after 3 decimal places. You can also move ground coordinates a few dozen feet if others are truncating at 6 (which is a reasonable standard). If the data is repeatedly exchanged between packages you can trash many routines by truncating any digits.
I agree there is a lot of overkill due to lack of understanding the math. Sometimes there is an explanation. .
Rankin_File, post: 327153, member: 101 wrote: "The CSF is different on the readme file, IFT file, TBC project and the CSF from CN# ####. If the CSF of 0.999531320 from CN# #### is used the accuracy is greater than 1:480,000." (emphasis mine)
To me the problem here is a failure of project management to establish a project scale factor for all consultants to use. If you leave consultants to their own devices with these matters you should expect, and be prepared to accept, variation in the results.
thebionicman, post: 327220, member: 8136 wrote: On an 1100 foot project with a 1:10k spec you can use 80% of your error budget stopping after 3 decimal places. You can also move ground coordinates a few dozen feet if others are truncating at 6 (which is a reasonable standard). If the data is repeatedly exchanged between packages you can trash many routines by truncating any digits.
I agree there is a lot of overkill due to lack of understanding the math. Sometimes there is an explanation. .
"I agree there is a lot of overkill due to lack of understanding the math. Sometimes there is an explanation."
Generally speaking they pick the number that they want for the project. So it doesn't really matter how many places are used, I suppose you could use a number like .999531000 but that seems silly. That number should stay fixed through the process from topo to finished build
thebionicman, post: 327220, member: 8136 wrote: On an 1100 foot project with a 1:10k spec you can use 80% of your error budget stopping after 3 decimal places. You can also move ground coordinates a few dozen feet if others are truncating at 6 (which is a reasonable standard). If the data is repeatedly exchanged between packages you can trash many routines by truncating any digits.
I agree there is a lot of overkill due to lack of understanding the math. Sometimes there is an explanation. .
"you can use 80% of your error budget stopping after 3 decimal places"
That wasn't very clear on my part, I was trying to say after the first 3 of the two 3's in the number (.999531320) or the 5th decimal place which would be 10ppm the 6th place would be 1ppm,