rfc, post: 359985, member: 8882 wrote:
2-14: 1068.22', S31-02-39W (from the survey).
2-14A: 1068.24', S31-04-22W (inverse from my adjusted network)I think Bill93's point about the short distance between 2-100 is a factor, but I've got several cross ties in there too, so at this point I'm not sure yet. That's why I think solar might help.
In reality nothing is wrong here. You have done an excellent job in retracing the record survey.
Adjust your traverse by holding coordinate 2, and rotating into 14. This will align your network to the record survey and both will be in harmony. Which should be your ultimate goal. Bill93 is correct, short baseline of your sun shot was then exaggerated many times over the additional traverse points "about 9x in going down to 14a". Every setup introduces more angular error. Chalk it up as a win. You did very well to have achieved 0.02' error over a distance of 1068.2' with multiple traverse points. That is precision of 1 in 53,4100. Twice that required for Second order Class B control work. GPS derived basis of bearing are very accurate over long distances, and very easy to reproduce with GPS. As you see, not so easy with a total station.
Clearly, as you have noted, the basis of bearing derived from a single baseline of just 100ft long is the source of your error. Distances are held over bearings for this reason.
Look at it this way.
Angle error in 0å¡01'43" over a distance of 100' is 0.05'
Angle error in 0å¡01'43" over a distance of 1068' is 0.53'
rfc, post: 359988, member: 8882 wrote: SP coordinates, but they're just the same US Survey feet
If I did it right, I found the combined factor for your location to be 0.999920 or 0.08 ft per thousand different between grid and ground. Perhaps worth applying, but not the size of discrepancy you are now looking for.
Cross ties are great for controlling the accumulation of errors, but if your only source of a bearing was a 100 ft line, then it's not surprising if everything is rotated a little.
Bill93, post: 360021, member: 87 wrote: If I did it right, I found the combined factor for your location to be 0.999920 or 0.08 ft per thousand different between grid and ground. Perhaps worth applying, but not the size of discrepancy you are now looking for.
Cross ties are great for controlling the accumulation of errors, but if your only source of a bearing was a 100 ft line, then it's not surprising if everything is rotated a little.
Thanks for the input. I went back and looked at the data put into Star*net and found I have only a SINGLE distance measurement between points 500 and 2. This distance could certainly "push" or "pull" the entire network (and point 14A) away from or towards 14. It's the only distance measurement that connects the entire network to point 2. I'm still working on getting solar into the act, but now have on my list of "To-Do's", a slew of additional observations between those two points. I know I could rotate the whole thing and pat myself on the back, but don't want to do that until I've squeezed every ounce of error out of my observations. Remember, I'm not doing this for a living (Thank the good Lord!).
RFC,
Just curious. What was to basis of bearings from your Surveyors plat?
Does the plat say:
1) Grid North
2) True North
3) Astronomic North
Most GPS surveys around here report the basis of bearings in GRID North.
The declination between GRID North and Astronomic North in your area is 0å¡02'29"
This is very close to your angular differences you noted above, which is 0å¡01'43"
leegreen, post: 360026, member: 2332 wrote: RFC,
Just curious. What was to basis of bearings from your Surveyors plat?
Does the plat say:
1) Grid North
2) True North
3) Astronomic NorthMost GPS surveys around here report the basis of bearings in GRID North.
The declination between GRID North and Astronomic North in your area is 0å¡02'29"
This is very close to your angular differences you noted above, which is 0å¡01'43"
Lee:
Grid North. You may be on to something, but I'll have to check my initial assumption/measurement of the bearing between 100 and 2.
I may have used the grid bearing from the survey, not astronomical. If I can get my solar worksheet corrected (your email regarding the semi-diameter may be right on point: I used the trailing edge and I may have an error in my calcs), I might be able to dial this in nicely. Stay tuned. Thanks for all your input.:stakeout:
For your information Grasshopper.
I don't like the term True North. It is a little ambiguous, and not specific. In my area, when a plat mentions True North, it often implies Astronomic North. True North can also be known as Geodetic North. The two are different by angle known as the Laplace correction, which in my area is about 7 seconds.
leegreen, post: 360026, member: 2332 wrote: RFC,
For your information Grasshopper.
I don't like the term True North. It is a little ambiguous, and not specific. In my area, when a plat mentions True North, it often implies Astronomic North. True North can also be known as Geodetic North. The two are different by angle known as the Laplace correction, which in my area is about 7 seconds.
Thanks for the head's up. The original bearing is clearly shown as being Grid, and, at the time, convergence was called out as 3'. I am cognizant of the fact that if I start throwing solar at my network, I will need to adjust for both convergence and LaPlace prior to putting into LSA.
rfc, post: 360049, member: 8882 wrote: Thanks for the head's up. The original bearing is clearly shown as being Grid, and, at the time, convergence was called out as 3'. I am cognizant of the fact that if I start throwing solar at my network, I will need to adjust for both convergence and LaPlace prior to putting into LSA.
I doubt you need to worry about LaPlace corrections with a solar.
MightyMoe, post: 360055, member: 700 wrote: I doubt you need to worry about LaPlace corrections with a solar.
I agree Moe. RFC will see more error in his measurements than LaPlace correction of 7 seconds.
leegreen, post: 360060, member: 2332 wrote: I agree Moe. RFC will see more error in his measurements than LaPlace correction of 7 seconds.
pretty sure we are way past them already...............
MightyMoe, post: 360066, member: 700 wrote: pretty sure we are way past them already...............
Hey, every second counts! Someday I might have a 1" gun, and will be staking out shade trees for my wife, to .0005' 😀
Remember, it's not about the destination; it's about the journey.:stakeout:
rfc, post: 360071, member: 8882 wrote: Hey, every second counts! Someday I might have a 1" gun, and will be staking out shade trees for my wife, to .0005' 😀
Remember, it's not about the destination; it's about the journey.:stakeout:
A matter of scale
traverse closures first, get that little traverse to about .02' of 3d raw closure total, get all the solars to match within 5", then start worrying about something like a laplace correction,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
MightyMoe, post: 360072, member: 700 wrote: A matter of scale
traverse closures first, get that little traverse to about .02' of 3d raw closure total, get all the solars to match within 5", then start worrying about something like a laplace correction,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Well, the results so far of this Grasshopper's maiden voyage using solar are in...with mixed results.
The procedure I used is one of the ones laid out in the Sokkia book...Set back sight to zero, then take three observations in succession (mine were about a minute apart). Then flip the gun; three more with reverse face, then the backsight in reverse.
The first three deviated from the mean by 6.5", 5.6" and .7" respectively. The second set not so good: 10.6", .3" and 10.9" respectively.
After applying Convergence, and La Place, the result put the azimuth of the line as little as 14" or as much as 44" off what I expected it to be (according to my previously rotated survey).
But what concerns me is the method of reduction of the data. Does BS-FS-FS-FS as a "unit" and then (reverse) FS-FS-FS-BS as a unit for determining the means of the observations really make sense? By "a unit", I mean use the Back sight related to the group to determine the measured angles. For some reason my reverse backsight was considerably off (179-59-12), and I don't know why...I suspect asymmetric heating of the tripod...I took the tripod out of the woods, where it was for several hours at around 40 degrees, quickly set it up in a large field; the sun was intense, and the temp was easily in the 60s if not higher, so I don't know if that's what the problem was.
But the question is this:
For HORIZONTAL angles, which is what we're doing here, is it even necessary to flip the scope and do the whole thing in reverse? I understand that because the sun is moving, every sight reduction is done independently...I'm not meaning anything first. So why not just do a back sight, then a dozen or more fore sights, reduce them, then mean the results?
You flip the scope to cancel any error due the line of sight not moving exactly in a plane perpendicular to the horizontal plane as you raise the sight. After you flip and turn 180, any such motion would affect the reading in the opposite direction.
That's important any time you have a big change in the vertical angle while reading horizontal angles. I've learned to always do D&R sets, however many of them I choose to do.
