True (if that's the current count of leap seconds), but most GPS receivers apply the difference to display UTC. However, what you need for astro work is UT1, which may be some fraction of a second different from UTC.
Polaris may have a less convenient schedule for the guy in the business of surveying, but I maintain that it is the desirable method because it can be very accurate with a lot less fuss (and a solar filter or) than either solar method.
> Those of you who use solar shots for azimuth,
> -Do you use the hour angle method or altitude method?
> -how do you do your timing?
> -what accuracy do you achieve?
When I made solar observations for azimuth with regularity, I used the hour angle method, timing pointings using the NBS radio time signal and a digital stopwatch for a comparing watch.
The expected uncertainty of a azimuth taken as the mean of three sets with a one-second theodolite was less that 1.5" standard error. Most were half that.
When I return to these projects with GPS, it's gratifying to see that the uncertainty estimates originally derived for the solars were quite good.
I tested the eTrex receiver I used against WWV to determine what time it was displaying. It matched UTC very well (as close as I could watch the LCD ticker compared to the tone from the scratchy radio), but Dave does make a good point. GPS time is not the same as UTC, but as Bill stated, consumer receivers often correct for this discrepancy.
I used the time function on the HP41 calculator assigned to a key so that it would freeze the display when I pushed the button. I set the time to WWV and noted the time correction of the double clicks. Eye on the crosshairs, finger on the button.
James
> True (if that's the current count of leap seconds), but most GPS receivers apply the difference to display UTC. However, what you need for astro work is UT1, which may be some fraction of a second different from UTC.
>
Not to co-op the thread, but...
One is supposed to use UTC (or UT1, with the correction). My iPhone "clock" runs both "Local Sidereal Time", and "Universal Time". Sidereal Time is 23 seconds later than UTC.
I've been using Universal Time. That's correct, no?
I haven't done celestial observations in years, but one time I did a bunch just for fun. I set a point in my back yard and used a radio tower for a backsight. I did solars and every star listed in the Sokkia ephemeris. It taught me where those stars are and what time of year they come out. Very rewarding!
We've hired graduates from MVCC in the past. They have very little hands on field experience, compared to students from Alfred and Paul Smith's. MVCC survey classes appear more class room oriented. Their students have a tough time setting up a tribrach and prism for a backsight. I think they should add a summer internship.
Lee Green
From what I've seen, any ephemeris that a surveyor might use for Polaris or the Sun uses Universal Time (UT1) as the time argument, so that is what you would use. Local sidereal time might come into play if you did a more elaborate calculation where you sighted some arbitrary star and determined the position of the star from a star catalog, but it would be an intermediate step in the calculations, not the starting point of the calculation. The difference between local sidereal time and UT1 is not a constant, even if your location is constant. Pondering the definition of each will make this apparent.
Local Hour Angle is what I am remembering in using on the HP41 and SMI on the HP48
There is an app "Navy Clock" that will sync newer versions of android with the atomic clock.
It will display hh.mm..ss in GMT and Local time of the Atomic Clock and your Phone Clock. Newer versions will sync the time of your phone clock to the Atomic Clock very quickly.
On older android versions it will display the 16± seconds of difference.
B-)
I believe it is very valuable to learn the old ways in surveying. Knowing how the land was laid out 100 years ago can help in you in retracing old boundaries, and how bad or good your matching the points. Precision isn't as big of a factor in finding old marks as the old marks hold over your precise measurements anyway.
Solar observations aren't used nearly as much as they used to be. But some guys still are doing it.
With the addition of a good clock, the hour-angle method is superior, but you really need to try to set your stopwatch as precisely as you can. The other method could get you much closer than using a watch back in the day when they didn't have access to accurate timepieces.
I got in this conversation late...you probably heard all I said before me. Anyway good luck.
I have not done a solar observation in two years. I use primarily GPS to determine Geodetic North at a point approximately in the center of my survey. For solar observations, I used the hour angle method and a shortwave radio that could tune in to WWV on 5, 10, or 15 MHz and listen to Coordinated Universal Time with the double tics indicating either a positive or negative correction, depending on whe the double tics started. I typically started my stopwatch at the fifth second as it was easier to time when to start the stopwatch. Anticipating the end of the five second "blank" from 55 to 60 seconds was difficult to do. I have done what Ken McMillan does and re-occupy old control points to compare old solar observation directions with new GPS directions and have been satisfied with the results.
I agree with others; learn all you can about geodesy, trigonometry, geometry, CAD, coordinate geometry, etc. The basic mechanics of learning how to use surveying equipment while in college will help when you get a real surveying job. I taught surveying in community college, and it is interesting to note that for a three semester credit hour course that has two hours of lecture and two hours of lab time each week, in 17 class meetings you would only get about 34 or less hours of field time the whole semester, which is less than one week of on the job training. Your real education will start on your first day of your new job. Just learn all you can before you get there, and talk to the old guys at work. They know a lot of tips and tricks that will make life much easier. And NEVER stop learning! I wish you the best.
I don't do them anymore, but I used to do them all the time, they were plugged into the data collector, needed to keep up with the time.
I would also often do them "longhand" from the booklet during lunch hour in the field, get time with a stopwatch and call in for the time, it would usually take about 5-10 minutes to reduce one.
I don't do them anymore but it is an important skill. Probably it would be best to not use much in the way of computer equipment during surveying class, once you know how to turn angles, close traverses, run levels, do solars, calculate coordinates, volumes, areas, reduce Lat, longs to a grid projection, everyday surveying with GPS becomes much easier.:-)
Here is an explanation of the difference between UTC and UT1 being DUT (or DUT1). When the DUT gets to about 0.8 seconds, then a leap second is applied. The chart in this link shows 13 leap seconds since 1985. Since GPS is at 16 seconds difference, I assume there were 3 leap seconds applied from the time GPS started and 1985.
http://en.wikipedia.org/wiki/DUT1
On WWV, the corrections will be positive if the double clicks are during the first 7 second. If the correction is negative, the correction will start at 9 seconds. UT1 is the time that should be used.
James
I just compared the Navy Clock II to the wwv radio and the app was a full second slow. I'm assuming it's because of the phones being a digital signal.
James
True, but 95% of our employer feedback indicates that it's the MVCC graduate they appreciate most after the first couple weeks. And our feedback from transfer institutions indicates they are the best prepared for the second two years.
Summer internships (and winter for that matter) are encouraged. But these are community college students with bills to pay, and the local surveyors generally will not pay as much as the local convenience store, so it's a tough sell.
So, it kind of depends on what one wants from an employee and what your vision is of what surveyors (technicians or licensed) should be in the future.
State ed. and the SUNY system are in agreement with you that field set up and equipment operation is the important thing and can be learned on the job; no need for education.
I've lost the argument, but I still disagree.
Ashleigh is one of my students and I didn't send her here. All the students get hit with opinions from the local surveying community on what should or shouldn't be in the program. I applaud her for taking initiative and performing more research in order to get a better sampling of opinion on her question. This is the kind of thing we are trying to instill in our students. Extra credit awarded in legal principles Ashleigh; keep up the good work!
:good:
> Im in college for land surveying, and in my surveying 3 class all were learning is sun shots. I'm just kind of wondering does anyone even do these anymore? I feel like we should be learning gps and stuff like that. I graduate in May and don't want to go out into the work force only knowing sun shots and basic leveling. Thanks in advanced.
First, if you can actually do one, and reduce it, by hand, then it's worth it's weight in gold because it gives you an understanding of mechanics of the operation. Leveling won't ever go by the way side, in my life time.
Learning "GPS" is a different in that you don't handle the observations, simply push buttons so it's not, in my opinion, as important and each unit is different so there is no one size fits all. That being said, once you understand one, the others are not so hard. The hat trick is the office reduction and analysis.
So I don't use them, but I know how, and I may very well need to use one again. It's handy to have in the tool box. Just remember what the old man taught me, make sure the filter is on the gun when you look at the sun, you'll only get two chances if it's not.
I think its important to learn how to do it, and why its done. But I haven't taken a sun shot in decades. i don't know may surveyors in my neck of the woods that still use sunshots.
Surveying can vary in use in various parts of the country.
I can teach someone to set-up a tri-brach easy enough. Having a new hire know the nuances of what we do and why its important is what makes a great employee/LS