The article talks about bench marks that may or may not have moved at the base of the monument.
Interesting the difference with the 1999 figure. Does anyone know exactly how the height is measured?
It all depends on where the Council of Tall Buildings determines the bottom of the structure. This is the difference in the "huge" elevation change.
http://www.ngs.noaa.gov/surveys/ngs/wm2013/
A buddy of mine worked for the Council and a similar issue came up with WTC1 as to if the spire was architectural or an antenna.
>
>> http://www.ngs.noaa.gov/surveys/ngs/wm2013/
There, it says:
"provided a rare opportunity for NOAA’s National Geodetic Survey (NGS) to perform a geodetic survey incorporating direct occupation of the WM peak with multiple instruments"...
Anyone care to venture what those "multiple instruments" might be?
It's probably just all the cold weather there lately.
Yep. Definitely cold weather shrinkage.
Ask the landscapers how much fill they added 🙂
Ask the landscapers how much fill they added 🙂
A few hundredths at the top due to lightning damage, the rest is at the bottom. Redefinition of "base at entry level". The brass plugs which previously defined the base are now buried in landscaping.
1999 survey
There's some pictures here. Dave Doyle was part of the group. Maybe he'll chime in.
Does anybody remember the cover of POB where they had a gps antenna with a special mount on the tip of the the monument? I could care less about a benchmark on the ground. I would like to see that gps data.
lol
I remember Dave D. and NGS on the Capitol Dome but not the Washington Obeliisk.
> I remember Dave D. and NGS on the Capitol Dome but not the Washington Obeliisk.
Dang, you're probably right. I remember two/three people in the picture though.
A complete description of what instruments were used and how the survey was performed can be found in the formal report for the survey, located here:
http://www.ngs.noaa.gov/PUBS_LIB/NOAA_TR_NOS_NGS_51_2015_02_16.pdf
For the answer to why this height differs from the 1885 height, see here:
http://www.ngs.noaa.gov/surveys/ngs/wm2013/2015%2002%2016%20Architectural%20Height%20Difference%20Explanation.pdf
And for just general information (and links to the 1999 survey too), go here:
http://www.ngs.noaa.gov/surveys/ngs/wm2013/
Dru Smith
Chief Geodesist, NOAA's National Geodetic Survey
P.S. The entire survey was done in metric units, but to ease comparison to historic data, we converted everything to the nearest 1/64 inch as well.
P.P.S. Here are some shots of the instruments involved...
Awesome Post Dru! Thanks for putting all that together.
