Astronomic AzimuthsPosted by john-hamilton on January 10, 2020 at 1:56 pm
The thread about the open traverse made me wonder if astronomic observations for azimuth is becoming a lost technique. I know a few people on here who them, some just for fun like me (haven’t needed to do one for a few years now)
- 57 Replies
- MemberJanuary 10, 2020 at 3:12 pm
I probably shouldn’t have voted because I’m not in the business, but did because I’ve done Polaris shots for projects in the past.
My most recent one was a bit different. The amateur astronomy club in the area is installing a better telescope in one of their domes (donated by a university that was done with it). It is big enough it had to be set in by a crane. The base is different from the previous one and needed a large adapter built to mount it. The base has to be aligned within a couple degrees of cardinal direction in order to be in range of final alignment.
We saw no practical way to bring in azimuth from outside up a circular stair, a magnetic compass couldn’t be trusted inside the steel walls, and you couldn’t see the ground outside from standing height. So I did a Polaris sight in the dome to establish a north-south line on the floor.
I used SPADE for my data, checked with Stellarium which agreed well enough for the purpose, and later by MICA which was quite close to SPADE.
That was quite an experience working in a cluttered and cramped 12 ft diameter enclosure in the dark with other equipment, a bench, and people moving around and twice bumping my tripod.
Our guess at north was off enough Polaris was not visible through the opening in the done until dark enough to see it with the naked eye and the dome turned. I was getting pretty frustrated that I couldn’t get az, el, and focus to happen on the star. My focus ring has enough slop that an infinity mark isn’t quite good enough.
We determined the old bolts in the concrete were indeed cardinal enough the adapter could use them for reference, a fact they had no prior reason to rely on.
The telescope is now mounted. The next challenge, after they get the control circuitry and software working, will be to finish the alignment so it is truly equatorial and accurately tracks a star..
- MemberJanuary 10, 2020 at 3:30 pm
I did them so frequently that it was part of the work flow.
My last one was in the early 2000’s in a mountain canyon where GPS couldn’t get a good fix.
By that time the program I had loaded up in my old DC for doing them, plotting the lat, long, updating time on the DC, and pushing a button as you observed the leading and trailing edges, was long gone and I had to do it by hand, some time later with better GPS I found out that I was about 30″ off, which I was very happy with.
It’s like dunking a basketball, it’s been 13 or so years since I did, don’t need to do it again (well,,,,, at least I can do a solar).
- MemberJanuary 10, 2020 at 3:49 pm
When I first started doing GPS, there was a limited time window, and we couldn’t do more than a couple of static sessions a day. So we set azimuth marks with polaris observations. One project I remember well was Prince William County in VA, I did 80 second order azimuths for 80 stations in a GPS blue book project using a Wild T3, in 1986 or 1987. I would observe GPS in the day on a 3 or 5 man crew, then go out at night if it was clear and observe astro’s. I was on salary for the GPS, but they were paying me extra for the astro’s. I could do up to 5 a night (16 positions) by myself, but usually got 3.
And we used to do a lot of eccentrics (before HARN/CORS) to tie in triangulation stations that were not occupiable, those were usually solars because we were close by and the accuracy requirement was a bit looser.
Haven’t done any on an actual job in probably 10 or 15 years. But I still mess around with them.
- MemberJanuary 10, 2020 at 6:25 pm
When working for the BLM in 1970 I had the privilege of being a member of a Cadastral survey crew doing multi-mile traverses in thick wooded country using a solar transit (Smith Solar Attachment). We’d take a solar shot when the sun was visible through the trees, several hundred over the course of the season. We’d also shoot Polaris using a T-2 with a right angle eyepiece prism once a week, surprisingly (for me) during daylight. Later when working for a County I convinced the boss to buy a Roelofs Prism for our T-2 which we used often for the same purpose, and for establishing orientation at sites (gravel quarries, etc.) with only one (or no) control station.
Of course when GPS became available solar accessories were relegated to the storage room.
- MemberJanuary 10, 2020 at 6:37 pmPosted by: @bill93
In case anyone is interested, here is the site:
A friend’s son welded the mounting adapter, which is a very heavy aluminum structure:.
- MemberJanuary 10, 2020 at 7:48 pm
I’ve observed the sun and Polaris as a sort of hobby but never at work.
I obtained an astronomic azimuth from my control spike in my front yard to a gate post about 500 feet away using Polaris several years ago. I then ran a GPS baseline and turned off the azimuth to get the geodetic azimuth. After applying the LaPlace correction they were within a few seconds of each other, I was surprised how closely they matched.
- MemberJanuary 10, 2020 at 8:25 pm
When I first started surveying back in Vermont, I was lucky enough to work for a company that did star shots on every job. It is a learned skill, and we got pretty good at it after awhile. I’m glad that I had the opportunity to do the observations and the calculations.
- MemberJanuary 11, 2020 at 1:38 am
Over the last 6+ years sun shots is my thing.
And there??s a lot more to it, but… better than 5? is not a stretch.
I wrote a comprehensive excel sheet with ephemeris included, which makes reduction a walk in the park. On repeat obs I hit 1-2 second at least 1/2 of the time. And agree with Gps to about the same
It is an art that needs to be kept up. I think you can learn a lot by doing it.
Solar azimuth is a great winter sport.
Question: what reduction software is popular? I only have E&K from the 80s and my own.
- MemberJanuary 11, 2020 at 7:27 pm
Back when LiDAR was a new thing it was all the rage to provide verification points for multiple ground covers. Often I would be able to get a single GPS point set in a clearing and use a solar backsite azimuth to gather shot in the dense forest. Have not done one in a decade. I did use my filter to view the solar eclipse.
- MemberJanuary 11, 2020 at 7:34 pm
I would like to do one, but I have been told several times that “it is an obsolete technique, no one does them anymore”. I always try to present at Trimble Dimensions, and I submitted several topics, that one they have never accepted.
I did attend two really great “classes” at NGS Corbin about astro observations a few years ago, it was a small class and we had a good time. We were going to try and make it an annual meeting, unfortunately the class organizer (Dave Lehman) passed away suddenly.
- MemberJanuary 11, 2020 at 7:46 pm
In 2011 and 2012 there was an astro class at NGS Corbin. Here are link to the classes that were given…
If anyone is interested, maybe we could do one again…
- MemberJanuary 11, 2020 at 8:03 pm
I’ve only done a Polaris observation once, as part of a class field exercise. If I were asked to do one today I’d have to go back to the books and start from scratch.
- MemberJanuary 11, 2020 at 10:09 pm
Yep, me also. We spent more time looking in the girls dorm than we did looking for Polaris.
- MemberJanuary 11, 2020 at 10:31 pm
There was a sun shot on the exam. And I didn??t skip over that question.
- MemberJanuary 11, 2020 at 10:40 pm
I worked for a shop that did one while I was there back in 2008 or so, it was on a Forest Service project if I recall correctly. I wanted to tag along but there was other work for me to do. Beyond that I have never heard of anyone doing one post GPS era.
- MemberJanuary 13, 2020 at 2:19 amPosted by: @alan-chyko
I don’t believe we covered this at all while at Penn State (97-99), but have always wanted to give it a whirl. I would love to attend a class on this.
I’m surprised that it wasn’t at least mentioned if you took surveying courses there, since Ghilani is from Penn State, and the Wolf & Ghilani Elementary Surveying book covers azimuth by Polaris in sufficient detail.
I cheat and use SPADE or MICA instead of going through the equations myself. The azimuth of Polaris given by the free program Stellarium is probably accurate enough for much work and the program is a lot of fun, too.
The advantages of Polaris are that time is fairly non-critical and you don’t need a filter. The disadvantages are that you need a right-angle eyepiece if you are above about 40 or 45 degree latitude (depends on your instrument), and have to do it outside normal working hours (twilight is best) unless you are in a place with very clear sky and have excellent instrument optics.
The problems with sun shots are the filter, the right angle eyepiece for some times of day, and very critical timing, but you can do them during normal working hours..
- MemberJanuary 13, 2020 at 2:59 pm
To do an astronomic Az observation you need a geographic coordinate and good time. In say 1981 to get a geographic coordinate for a solar observation the method was to plot your location on a quad sheet and interpolate the coordinate.
This of course introduced error, then to get accurate time varies methods were used, one surveyor would listen to his radio and sync his watch to the time stamp at the beginning of each hour, or you could call the number in Colorado and sync to it.
Of course, now there are better ways to pin down your location and your time, I see some statements of solar’s within 5″ which wasn’t possible in the field doing real work just a few years ago.
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