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    Re: Sextant practice, experimentation --Saturday in RI.
    From: G Becker
    Date: 2013 Oct 4, 14:24 -0400


    I only use levels to run elevation. Systematic errors in total stations are usually vertical, no matter the level persnickety you practice. Newer total stations have compensating software to correct the systematic vertical errors…. But it is still there, just covered up with a software Band-Aid. None of this really matters, as long as you had a good time at the water’s edge. One thing I’ve noticed over the years and this is a general elevation. At the edge of the high tide line... the plants go from cord grass in the water, to pickle weed, to a sea oxeye daisy. The sea oxeye daisy “usually” grows at 6.0 to 6.5ft on the 1929 NGVD elevation datum.


    By the way, there should be an NGS calibration baseline in or near your town. Ask your survey guy where it is located. They are usually at the local airport or any safe location with 3500 ft of open space.




    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Bruce J. Pennino
    Sent: Thursday, October 03, 2013 9:40 PM
    To: george@gwbeckerpls.com
    Subject: [NavList] Re: Sextant practice, experimentation --Saturday in RI.




    A few comments and a major " thank you very much "  for information regarding the bench marks. I also found the bench mark info.  


    When I arrived at Beavertail the site was very busy with visitors and cars.  I quickly decided that would not even try to find a BM or "run a line".  The nearest existing one (still clearly existing ) was some distance away.  It was an easy climb down to the waterline and I figured for CN it would be good enough to "tie in" to a nearby tidal gauge.  There are several gages nearby and FER knew of corrections and other related information. FER held the prism pole and I shot the vertical distance from the height of eye (theodolite) to the prism. Adding the prism pole plus a small additional vertical distance because the bottom of the pole was not in the water gave us a total height at that point in the tide.By happenstance,the ground at the theodolite was about  the same elevation as the new finished slab at the former lighthouse.


    MORE or LESS, the slab and ground  elevation  at the fog horn is Elevation 25.0 MSL.. At this site the normal average monthly tidal range from MLW to MHW is about 3.5 ft or so. I would feel very comfortable standing on this slab and using a HoE 30 or 31 ft and then correcting a bit for  actual tide  ......good enough by any reasonable standard.


    The dip was NA  almost "right on"  at 0.96sqrt H ft when we did the lunar  measurements. Height of eye 29.6 ft. Measured dip 5.2 minutes .  My Ho - Hc with the total station sights was Ho - Hc = 0.2 minutes of arc. Air temp 64F, water temp 65 F Atmos Press 30.27", wind at 8 mph, sunny, ocean calm and looking out toward the Atlantic


    Regarding "bad practice" of using a theodolite for running elevations .......... maybe yes, maybe no. It depends on exactly  the goals, accuracy, and device.  A modern total station (like mine) is more than adequate for running elevations where standard surveying accuracies are required.   I've personally checked elevations obtained with my total station(theodolite) against a newer total station and my results agree to within plus or minus 0.02 ft at distances up to 500 ft.  This is how I check my calibration because there is no convenient place for me to check against a verified "standard". The guy I check against is an absolute fanatic above accuracy since he often surveys in cities where I believe the lowest quality is 1:25,000? Maybe 1:50:000?


    I think I have now picked up any "loose ends".

















    ----- Original Message -----

    From: G Becker

    Sent: Thursday, October 03, 2013 12:13 PM

    Subject: [NavList] Re: Sextant practice, experimentation --Saturday in RI.




    I was not present at the meeting. It was mentioned a geodetic monument was located at the site. The pdf file I attached listed all the geodetic monuments at that location and their reference points. I realize the information was after the fact, but I assume Frank and others live near the site. Using the monument Beavertail and back sighting the reference monuments, a person could set a new reference point at the waters edge. The new reference point could have a “precise” possibly accurate location and elevation*, usable at any desired time in the foreseeable future.


    * Running elevation with a theodolite is a bad practice.


    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Antoine Couëtte
    Sent: Thursday, October 03, 2013 11:22 AM
    To: george{at}gwbeckerpls.com
    Subject: [NavList] Re: Sextant practice, experimentation --Saturday in RI.


    RE : http://fer3.com/arc/m2.aspx/Sextant-practice-experimentation-Saturday-RI-Pennino-sep-2013-g25232

    Hello Bruce,

    Hello to you too M. G Becker,

    Thanks for your data.

    Sorry for my query : what was exactly your WGS 84 Position ? I am a bit confused at the explanation given in " http://fer3.com/arc/imgx/BEAVER-CONTROL.pdf " as an appendix to " http://fer3.com/arc/m2.aspx?i=125240 " by G Becker .

    Best regards


    Antoine M. Couëtte


    Re: Sextant practice, experimentation --Saturday in RI.
    From: Bruce J. Pennino
    Date: 2013 Sep 29, 10:08 -0400
    Previous messageNext messageReply to this message

    We met at Beavertail Light and had a good day. Perfect weather. The "Light" Association is building a new platform on the old Light Foundation. FER and I surveyed the elevation of the ground on the south side of the road, just south of the fog horn device; at the edge of the bluff. The ground at this point is very close to the elevation of the new platform. The ground elevation is 25 ft more or less above MSL. FER may want to refine this value.

    With my total station I had a HoE of 29.6 ft when I measured a dip angle (mean) of 5 min 14 seconds. Air temp was 64 F, water temp, 65 F, atmos. P 30.27 ", Wind {at} 6 mph. Frank and I used the theodolite to sight the UL of moon. I read the angles and FER observed time GPS/UT

    Herewith are the ZENITH angles where 0 deg is vertical with times:

    GMT/UT 16 hr 36 min 38.3 seconds ZD 66d 18' 09"

    16 hr 37 min 42.7 seconds ZD 66 d 30' 03"

    The fractional second of time is estimated by FER

    An excellent location for walking, picnics, and CN observations. Crowded and busy on weekends, but plenty of parking.

    Best regards,

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