Strategy for determining the basis of Bearings of a control network; Part II

rfc

I would like to make some comments on your work.

1. When you do astronomic work it is best to have your backsight at least 1km away.
2. In turning angles a "set" is considered as D&R on backsight and D&R on foresight. Does not matter how many targets are between the backsight
and foresight when you are done (D backsight, D foresight, reverse telescope, R foresight, R backsight = 1 Set.
3. Having a target sitting on the ground as you show in one of your pictures is not a good idea (refraction).
4. Its great to try different stars for azimuth; BUT it would be best to stay with a circumpolar star, like Polaris ( in the northern hemisphere)
and at; east or west collimation till you really get good at observing (say 20 different nights and 16 D&R on each night). Then go to Polaris at any hour angle, 16 D&R again and on 30 different nights. Then try different stars.
5. A astronomic azimuth will be different from a GPS derived azimuth; because________________________. Fill in the blank.

JOHN NOLTON

JOHN NOLTON, post: 373439, member: 225 wrote: till you really get good at observing

So he took the average of 4 solar azimuths, observing the trailing edge of the sun. And an Astro azimuth observation to Arcturus. And the average solar az is 1.7" different than his Arcturus azimuth. But he'll get better at observing.

JOHN NOLTON, post: 373439, member: 225 wrote: 5. A astronomic azimuth will be different from a GPS derived azimuth; because________________________. Fill in the blank.

So if one accounts for deflection of the vertical and Laplace to correct Astro az to (near) geodetic, what sort of differences have you experienced?

JOHN NOLTON, post: 373439, member: 225 wrote: rfc

I would like to make some comments on your work.

1. When you do astronomic work it is best to have your backsight at least 1km away.
2. In turning angles a "set" is considered as D&R on backsight and D&R on foresight. Does not matter how many targets are between the backsight
and foresight when you are done (D backsight, D foresight, reverse telescope, R foresight, R backsight = 1 Set.
3. Having a target sitting on the ground as you show in one of your pictures is not a good idea (refraction).
4. Its great to try different stars for azimuth; BUT it would be best to stay with a circumpolar star, like Polaris ( in the northern hemisphere)
and at; east or west collimation till you really get good at observing (say 20 different nights and 16 D&R on each night). Then go to Polaris at any hour angle, 16 D&R again and on 30 different nights. Then try different stars.
5. A astronomic azimuth will be different from a GPS derived azimuth; because________________________. Fill in the blank.

JOHN NOLTON

John:
Thanks very much for the input. I'm really back sight challenged at my location. I have a distinctive corner of a house about 1.2 km distant I can use for AM solar (It's less distinctive in the PM), but useless for astro unless I'm right on time with the stars, before the place becomes invisible; haven't asked the people who own it if I can mount a strobe on the roof, lol. There's no way I'd be able to see the house with polaris, as the optics on my Topcon just aren't good enough for daytime observation. I've tried before and will again, but I'm not optimistic.

Comment regarding ground mounted back sight noted, but given the short distance (275'), refraction is unlikely to be an issue, and even if it was, it wouldn't be of the same magnitude as centering errors with a tripod mounted back sight.

I've only begun, and will be looking at Polaris soon; Have right angle, so crooked neck syndrome will not be an issue.

As for 5....can't comment; know nothing about it yet.

JOHN NOLTON, post: 373439, member: 225 wrote: rfc

1. When you do astronomic work it is best to have your backsight at least 1km away.
JOHN NOLTON

John:
I forgot to ask: I understand the theoretical reason to use a distant backsight, but as a practical matter, If one is trying to establish an azimuth on a project, why go to the trouble to use a distant back sight (assuming none is contained within the project itself), if, in the end, you're going to turn sets between the back sight and one or more stations in your network? You're still observing the local marks with the same gun, the same targets, the same uncertainties, the same number of times.

If you assume equal number of observations from Star to Station, vs. Star to Back Sight and Back Sight to Station, and put them all into Star*net, intuitively, I think the results would be the same, wouldn't they?

rfc

Thanks for making it clear to me about your problems with short backsight, house in the way for Polaris and for letting me know what type of instrument you have to use.

The reason for a long ( 1 km) backsight on astro. is you don't want to change focus; If you were using a Wild T3 there is something called "draw tube error" which can cause an error of 1.5 seconds (+/-). This is very bad for 1st order work (it can be corrected in a repair shop if they know what they are doing) This would be NO problem in your work.
Observing Polaris in the daytime. Yes I have had much trouble "trying" to observe Polaris in the daytime with my Wild T2( and a special note here;
you never want to change focus during daytime observations on any star because when you try to find it again it will be near to impossible).
Two places I could observe Polaris in the daytime with my Wild T2 was Montana and Canada. All other times I just get the 2 big boys out, Kern DKM3
or the Wild T3. The man that taught me the daytime observation with the T2 (in Canada) would use a marking pen and mark the tube and focusing ring
with a line so here new where focus on the star was.

rfc, two more questions for you on astro. 1. What are you using for time? 2. What state do you live in?

JOHN NOLTON

PS the reason I want you to observe Polaris first and for many times is get used to the star moving and tracking it. As you have seen that when you observed Arcturus in is moving much faster than a circumpolar star.

Have fun and let me know how you are progressing.

JOHN NOLTON, post: 373533, member: 225 wrote: rfc

Thanks for making it clear to me about your problems with short backsight, house in the way for Polaris and for letting me know what type of instrument you have to use.

The reason for a long ( 1 km) backsight on astro. is you don't want to change focus; If you were using a Wild T3 there is something called "draw tube error" which can cause an error of 1.5 seconds (+/-). This is very bad for 1st order work (it can be corrected in a repair shop if they know what they are doing) This would be NO problem in your work.
Observing Polaris in the daytime. Yes I have had much trouble "trying" to observe Polaris in the daytime with my Wild T2( and a special note here;
you never want to change focus during daytime observations on any star because when you try to find it again it will be near to impossible).
Two places I could observe Polaris in the daytime with my Wild T2 was Montana and Canada. All other times I just get the 2 big boys out, Kern DKM3
or the Wild T3. The man that taught me the daytime observation with the T2 (in Canada) would use a marking pen and mark the tube and focusing ring
with a line so here new where focus on the star was.

rfc, two more questions for you on astro. 1. What are you using for time? 2. What state do you live in?

JOHN NOLTON

PS the reason I want you to observe Polaris first and for many times is get used to the star moving and tracking it. As you have seen that when you observed Arcturus in is moving much faster than a circumpolar star.

Have fun and let me know how you are progressing.

John:
Thanks for the further clarification. If the only reason for the long back sight is focus, I've got that covered. I've marked my focus ring; no problem with focus; I thought the reason was for more precision compared to something close. Just to clarify, the "House" is not in the way for Polaris; the "House" IS the back sight...it's so far away though, and in the shade, I can't see the corner I've been using well enough once dusk falls.

As for tracking the stars...I think I have that down too: I set my back sight at it's (now fairly accurate) real azimuth. Then, using MICA on my laptop, put up Azimuth and Zenith angle for the star at 1 minute increments. I look at the time; dial in the numbers and Poof! if it's dark enough, there she be.

Got time down too: I'm using Emerald and Sequoia time, which is known good time, comparing three or more time servers. It's never been off when I set my stopwatch going by more than .01" or so. Then (thanks to Larry Scott's input), I lay down a bunch of "test" split times at 30 second intervals prior to an observation session, and again after the session to check in with Sequoia. Larry's sheet then computes the standard deviations of the presses and applies that to the time calc. My stopwatch can hold up to 60 splits, which is enough for two full sessions on an object plus the test splits.

Finally, I'm in Vermont; 43N +/-

rfc, post: 373423, member: 8882 wrote: In this thread, started some time ago:

https://surveyorconnect.com/community/threads/strategy-for-determining-the-basis-of-bearings-of-a-control-network.325735/page-2
Some made comments such as:

After a "dry run" between two NGS marks nearby to prove I could do it, (that resulted in sub 10" accuracy), I've recently completed some more work on developing a basis of bearings for my control network. I did 4 full sets (8 D, 8 R) of Solar between two points on my network, and then did Arcturus (8 D, 8 R) for the same two points. Some uncertainty might have been added by using a distant "intermediate" backsight point, per Robert Hill's suggestion in the same thread noted above.

The azimuth delta (all using Larry Scott's Excel Masterpiece in Process), between the two, was 1.7" of arc in azimuth. That's with a "5-second" gun. Beginners luck? Maybe, but stay tuned. Much more to come.

Now all I need is to borrow someone's old L1 GPS rover and base for a month or so to prove that astro can be as accurate (for azimuth), as GPS.:stakeout:

Just a follow up.. since my name came up here. Not sure exactly what you mean as an intermediate sight but I have an idea.
I attended the Univ. Of Arkansas (Fayetteville ) studying Land Surveying in 1982-85.
This was Dr. Knowles program and I was very fortunate to receive his instruction in solar observations.
It was at this time, the Dr. Knowles along with Dr. Senne and Elgin were developing the Solar Ephemeris and associated programs for Leitz. As a student, I performed an abundant amount of solars on the campus during survey labs. We would set up on hubs outside of the Old Main Bldg. Two man operation. I-man and note and time keeper. All calculations were done on a HP 11C calculator. Instruments used were Wild T2s or T16s, Kern and some Leitz guns. Everyone preferred the T2s. Sightings would be on a church steeple in downtown Fayetteville. I learned a lot.
Expected accuracy always fell in the 6‰Û range. Time was important along with the sighting. Viewing the sun was the easy part. I don‰Ûªt know if we were ‰Û÷lab rats‰Ûª for the Knowles, Senne and Elgin work but it was be safe to assume that our student data w added to their research as a redundant material.
Upon moving back to Louisiana, I was hired on my first job because I was able to run a South line by solar through 3 miles of challenging marshland (many stream crossings) on the north side of Lake Pontchartrain. I used a K&E paragon transit.
One fond memory‰Û? On one of the first observations. I was the I-man and I had a young fellow student from Kansas keeping notes and time. When I attained the solar pointing on the edge, I would say ‰ÛÏMark‰Û so the time could be recorded. I thought we were on the same page as they say but when I said ‰ÛÏmark‰Û all I heard back was ‰ÛÏWhat?‰Û I got the sighting again and said ‰ÛÏmark‰Û and once again I heard ‰ÛÏWhat‰Û. Well, his first name was Mark and he didn‰Ûªt know that I was telling him to mark the time.
I told him from that point forward that I would say ‰ÛÏtime‰Û and always call him by his last name.

John Nolton has given you good advice.

We also trig levelled the top of the towers too.

Robert Hill, post: 373650, member: 378 wrote: Just a follow up.. since my name came up here. Not sure exactly what you mean as an intermediate sight but I have an idea.
I attended the Univ. Of Arkansas (Fayetteville ) studying Land Surveying in 1982-85.
This was Dr. Knowles program and I was very fortunate to receive his instruction in solar observations.
It was at this time, the Dr. Knowles along with Dr. Senne and Elgin were developing the Solar Ephemeris and associated programs for Leitz. As a student, I performed an abundant amount of solars on the campus during survey labs. We would set up on hubs outside of the Old Main Bldg. Two man operation. I-man and note and time keeper. All calculations were done on a HP 11C calculator. Instruments used were Wild T2s or T16s, Kern and some Leitz guns. Everyone preferred the T2s. Sightings would be on a church steeple in downtown Fayetteville. I learned a lot.
Expected accuracy always fell in the 6‰Û range. Time was important along with the sighting.

Robert:
Very cool indeed. We're paying close attention to time. At 15" of arc of travel every second of time, it's essential. My stopwatch punches standard deviation is in the .1 second region, and the time itself from Emerald and Sequoia is a tenth of that (.01"). Did your 6" accuracy take include deflection and LaPlace? Was 6" the expected norm at the time?

At 1.7" it sounds as if you've exceeded the specs of the instrument and the quality of the ephemeride data.
The control probably isn't that precise based on the error ellipses.
Sounds like it's Miller time.
:-D:beer:

Scott Zelenak, post: 373777, member: 327 wrote: At 1.7" it sounds as if you've exceeded the specs of the instrument and the quality of the ephemeride data.
The control probably isn't that precise based on the error ellipses.
Sounds like it's Miller time.
:-D:beer:

As for the Ephemerides, Robert Hill will be pleased to know that the sheet I'm using is within an arc second of Elgin and Knowles ASTRO83 program (circa 1985).
As for control, by the time I'm done, I'll have dozens of redundant measurements between the two points I'm using for astro, and hundreds for the entire network, so I'm pretty sure that after adjustment, my control is going to be tight tight tight.
Finally, I've yet to analyze comparing astro observations performed Pre-Miller time vs. Post-Miller time. It's on my list.:beer::beer::beer:

[USER=8882]@rfc[/USER]
Next time you visit Arkansas, drive up to the Lodge at Mount Magazine, find monument "KNOWLES" and make a solar observation in honor of Dr. David Knowles.
http://www.ngs.noaa.gov/OPUS/getDatasheet.jsp?PID=BBBC60&style=modern

Give me a shout and I'll meet you there for a beer...after a foot race to the highest point in Arkansas...winner buys.

DDSM:beer::beer::beer::beer:

Dan B. Robison, post: 373914, member: 34 wrote: after a foot race to the highest point in Arkansas...winner buys.

Maybe, with your bad knee, you should try something a little easier, first:

B-)

By "control" I meant the two NGS disks.

And really nice work.

Dan B. Robison, post: 373914, member: 34 wrote: [USER=8882]@rfc[/USER]
Next time you visit Arkansas, drive up to the Lodge at Mount Magazine, find monument "KNOWLES" and make a solar observation in honor of Dr. David Knowles.
http://www.ngs.noaa.gov/OPUS/getDatasheet.jsp?PID=BBBC60&style=modern

Give me a shout and I'll meet you there for a beer...after a foot race to the highest point in Arkansas...winner buys.

DDSM:beer::beer::beer::beer:

Dang it Darn Dan‰Û?
I didn‰Ûªt know that was there. We were at the Magazine Lodge in 2007. The year before, our Katrina evac plan was to Hot Springs and we checked in at the Arlington for what we thought would be a day or two vacation then the levees broke and It turned out to be a 10 day stay, then we wandered over to Pensacola to gather up with the rest of the family who were displaced. Surreal times.
The people of Hot Springs were extremely kind to all the Louisiana castaways of the disaster. So much so, that next summer we decided to revisit to pay back some of their kindness. We stayed in Hot Springs again for a few days and then headed up to the lodge for a few more days. Beautiful place. I took our 5 yr old on a hike to the top of Mt. Magazine. We went into Paris to shop and went to a vintage Wal-Mart where my wife bought a nice blouse. Whenever anyone asked where she got it, she would reply. ‰ÛÏRobert took me to Paris and I bought it there‰Û It was a very nice blouse. We also had some pizza in Paris at a place that was recently opened by some displaced Louisianans. Our boy was looking at one of those coin machines that sell various sort of tchotchke for 50 cts or so. An elderly local saw him looking at the trinkets and went over an put money in and gave him the item. It was small imitation shark tooth key chain and it became a treasure to him. I still have it. It is attached on a string with various other trinkets (alligator tooth, glass beads etc. and it has hung from the mirror of my vehicles as a traveling talisman.
Folks at the Lodge were so nice. We had left an item of great value to us in the room and they sent it down to us afterward by Fed-Ex.
I wish I had known that disk was there.
Speaking of Paris‰Û?When I lived In Fayetteville in the early 80‰Ûªs, I would do things on whim. I liked to take off and hit the back roads. A week or so before Christmas on a cold day, I decided to drive to Mt. Magazine and do some Christmas shopping in Paris. He trip to Mt. Magazine was uneventful. There ws nothing really there besides the top. Going into Paris, I saw the old Paris General Hardware store. I went in to shop. It had the largest pot belly stove that I ever saw for heating the place. It was dark inside with a few bare light bulbs. The sole proprietor was there and naturally was wary of my presence. It was evident that everyone was now shopping at Walmart or other places. It was a twilight zone experience. I found a load of items to buy. Old cast iron and enamel cookware. Pocket knives, hurricane lamps, hand tools likes adzes and draw knives plus many other small items. All vintage stuff layered in dust and some stove soot. It was like being there in the1940s or 50s with the original prices. I felt like I was in a Donald Harrington place whom I recently had met in Fayetteville at the Dickson Street Bookstore browsing one day. Everyone enjoyed their gifts from Paris that Christmas
I still have the Case bone hunting knife. It is right here in my desk draw.
pictures from the lodge stay

[USER=378]@Robert Hill[/USER]
Robert,
Mark your calendar for Sept. 22 & 23, 2016 for the ASPS Fall Short Course at Mt. Magazine.
http://www.arprofessionalsurveyors.com/events/EventDetails.aspx?id=807287
Maybe we can talk Viiram to buy the beer.
DDSM:beer::beer::beer:

JOHN NOLTON, post: 373439, member: 225 wrote: rfc

I would like to make some comments on your work.

1. When you do astronomic work it is best to have your backsight at least 1km away.
2. In turning angles a "set" is considered as D&R on backsight and D&R on foresight. Does not matter how many targets are between the backsight
and foresight when you are done (D backsight, D foresight, reverse telescope, R foresight, R backsight = 1 Set.
3. Having a target sitting on the ground as you show in one of your pictures is not a good idea (refraction).
4. Its great to try different stars for azimuth; BUT it would be best to stay with a circumpolar star, like Polaris ( in the northern hemisphere)
and at; east or west collimation till you really get good at observing (say 20 different nights and 16 D&R on each night). Then go to Polaris at any hour angle, 16 D&R again and on 30 different nights. Then try different stars.
5. A astronomic azimuth will be different from a GPS derived azimuth; because________________________. Fill in the blank.

JOHN NOLTON

I looked at Bob's observations, and some advice on observation and reduction.
This isn't a whole lot of data, but the repeatability looks good.
The question is "how close to geodetic is his onsite azimuth observation?"

All astronomic to geodetic conversions applied,
UT1 time source internet NTP (feedback loop, network time protocol)

To repeat Bob's summary:

the off-site control points. (Laplace -2.8")
inverse between published NGS pts
175-25-56.8 pub

Very clean data,
175-25-58.9 (2.1" to inv) sun
175-25-59.7 (2.9" to inv) Arcturus

These had some apparent issues reported in the notes, and noted before reduction:
175-26-01.6 (4.8" to inv) Polaris
175-26-04.4 (7.6" to inv) sun
________________________________________________________

Onsite, repeat azimuth observations. No GPS inverse comparison. (Laplace -4"):
327-58-33.7 sun
327-58-32.6 sun
327-58-32.3 sun
327-58-32.3 Arcturus
327-58-32.7 average

Additional observations, very good looking data, however, 5" different. :
327-58-37.7 sun morning
327-58-37.3 sun afternoon
Too soon know which is more accurate No apparent reason for the 5" difference

Larry Scott, post: 375333, member: 8766 wrote:
The question is "how close to geodetic is his onsite azimuth observation?"
________________________________________________________
Onsite, repeat azimuth observations. No GPS inverse comparison. (Laplace -4"):
327-58-33.7 sun
327-58-32.6 sun
327-58-32.3 sun
327-58-32.3 Arcturus
327-58-32.7 average

Additional observations, very good looking data, however, 5" different. :
327-58-37.7 sun morning
327-58-37.3 sun afternoon
Too soon know which is more accurate No apparent reason for the 5" difference

OK. So, armed with the expectation of nailing an azimuth using astro within let's say for argument, 3" or so, this armament coming from two known NGS monuments with a published inverse, I move to the site of my control network (where the "327..." observations were taken). As Larry says, there's no "GPS inverse comparison", but there is this, from a neighboring survey:

It goes on to say it conforms to accuracy standards for a "rural class survey as established by part 5 yada yada of the Rules of Vermont yada yada". If my memory serves me correct, it's 5000:1 closure.

There are a number of bearings on this survey between points that are anywhere from 100' to about 300' apart. Is there enough information here to determine the azimuthal error eclipses associated with the survey? Or is the devil in the details with GPS...how long on a point, whether static or RTK etc. Quality of the data, etc. When you submit data to OPUS does it come back with such data? I've chatted with the surveyor that did the work, but didn't feel comfortable keeping him on the phone for hours asking questions. (This place is different, bless you all):-)

So, put another way, If I do another half dozen or so observations from my master control point to a slew of bodies, will I be within the margin of error shown on the adjacent survey? This azimuth will eventually be headed to Star*net, so I'll need to quantify the error for that purpose.

Assuming the neighbor's survey is accurate within expected tolerance. And is cited as SPC bearings.

Your survey of the common lines will probably have a different azimuth. Q: how much different? If it's a near constant, then it's a rotation. And that's of little concern.

A difference of 3" in 1/2 mile is only a few hundredths.

For your survey you should adjust it to a) your own data. b) holding the neighbor's azimuth of the longest common line. (The azimuth between the 2 common points that are farthest apart.)

If there are a few monuments on the common line, shown as a straight line, then all you want to verify is "are they in a straight line? And the distances between them."

Even if the neighbor's survey is rotated by degrees from SPC, and the bearings between points demonstrate a straight line, then that's point. However, perusing a good and true SPC azimuth to match the neighbor's survey is a good start. But if it's different, that doesn't effect that survey. You can determine if the points on the common line are where they are indicated to be, relative to each other.