A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
Date: 2003 Mar 19, 08:22 -0700
Here is the explanation that I have for interpretation of the information shown below: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ A positive meridian component of deflection of the vertical (Xi) indicates that the astronomic latitude will fall to the north of the corresponding geodetic latitude of the point. A positive prime-vertical component of deflection of the vertical (Eta) indicates that the astronomic longitude will fall to the east of the corresponding geodetic longitude of the point. The computed Laplace correction (Hor.Laplace) should be ADDED to a clockwise astronomic azimuth, to obtain a "near-geodetic" Laplace azimuth. Note: the deflection correction is usually negligible, yielding a geodetic azimuth. Note: in many textbooks, the Laplace correction is shown with the opposite sign and is subtracted from astronomic azimuth. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ So it looks like the astronomical location for your location is too far south by about 2.72 seconds ( about 300 feet). Hopefully I am interpreting this correctly. ----- Original Message ----- From: "Fred Hebard"
To: Sent: Tuesday, March 18, 2003 8:05 PM Subject: Help with interpretation of deflection from the vertical > I downloaded one of the programs from the geodetic survey site > referenced by Doug Stephen, and I also ran the online version of > Deflec99, but I'm having trouble interpreting the output. > > Deflec99's output from the interactive version for my location was: > > latitude longitude Xi Eta > Hor Lap > Station Name ddd mm ss.sssss ddd mm ss.sssss arc-sec arc-sec > arc-sec > USER LOCATION 36 46 48.00000 80 50 42.00000 -2.72 > 0.61 -0.45 > > > The intd routine, also from the Deflec99 folder, gave an output of: > > latitude longitude Xi Eta > Hor Lap > Station Name ddd mm ss.sssss ddd mm ss.sssss arc-sec arc-sec > arc-sec > Our House 36 46 48.00000 81 50 42.00000 -2.14 > 0.33 -0.25 > > > For comparison the output for a location near Denver, Colorado, gave: > > latitude longitude Xi Eta > Hor Lap > Station Name ddd mm ss.sssss ddd mm ss.sssss arc-sec arc-sec > arc-sec > USER LOCATION 40 0 0.00000 105 5 0.00000 2.06 > 13.22 -11.09 > > > The basic question is, what does this mean? The readme for Deflec99 > discusses deviations in azimuth, but deviations in altitude are > mentioned less frequently. > > Thanks, > > Fred