California Surveyors Forums

I’ve been hired to stake a satellite pad & bolts oriented at a specific azimuth based on true north. Our contract requires us to lay it out based on true north via “manufacturer methodâ€￾. The method stated per the manufacturer requires use of a theodolite observing the sun and utilizing the ‘appropriate almanacs’. I know a lot of us have studied this, but I was hoping someone could verify my method is correct as to how I interpret the ‘appropriate’ method to do this. I am also going to do static GPS on a couple of the project control points to verify my solar observation calcs with post-process calc’d geodetic north (I realize I could get this solely via GPS, but in case held liable, we want to do it their way and ours…and this is fun!).

I’ve obtained the sun azimuth via Form B (lower on the page) @:

http://aa.usno.navy.mil/data/docs/topocentric.php

|Is “Apparent Topocentric Azimuthâ€￾ the appropriate azimuth to use in determining suns HA rotation from true north at a given UTC time? The astronomy sites offer a lot of new vocabulary, but as far as I can tell Topocentric is what we’re looking for. Additionally, I will be observing the trailing edge of the sun for better precision, compensating for the suns semi-diameter via the “semi-Diâ€￾ listed per table:

www.cadastral.com/2013apr.htm

I want to get this right the first time, any comments/suggestions for those lucky few that have gotten to do this kind of stuff in the past would be greatly appreciated. Thanks.

Call Jack Sparrow, LS 666X.

Jack Sands LS 3379 had a pretty good presentation on the hour angle method in the Caltrans Video Exam study guide:

http://www.dot.ca.gov/hq/row/landsurvey ... okTOC.html

LS_8750 wrote:Call Jack Sparrow, LS 666X.

lost his sextant when the Black Pearl went down. perhaps his 'compass that doesn't point north' may be of help?

Perchance that ye do call him, he prefers "Captain" Jack Sparrow.

Be ye warned, that the Commadore believes that Mr. Sparrow is quite possibly the WORST priate he has ever seen.

:)

Woodcutter wrote:.....

Consider polaris observations. For high accurate work, you may get better results.

I agree.
I've done both on the same projects and Polaris shots are much easier and more accurate due to the distance and slower perceived movement. I would go with that if you are concerned with accuracy.

My $0.02

I don't know...over the years I have done an awful lot of reading on celestial observations and have never to my recollection seen such a term.

I used to do these all the time and it sounds like you are on the right track. I would recommend that you have an accurate time piece, preferably using atomic time and coordinating time lapse from office to field and back again. Trailing edge is best as the sun moves very fast. Beware of daylight savings time with the almanac although that would create a huge noticeable error. I used to double check with a compass compensating for isogonic movements.

Thank you guys for the help and suggestions. I got it all in there, GPS and solar checked <30 secs (tolerance was 15 minutes), pretty cool stuff. Thanks!