# LTE: Letters to the Editor

Shelly:

I read the article “Gravity’s Increasing Gravitas” by Kelly Bellis, PLS, with great interest. We (the survey community) in Louisiana are experiencing large vertical discrepancies in the translation from ellipsoidal heights to orthometric heights (elevations) because of distortions in the empirically derived geiod model presented by NGS. When will part two of Bellis’ article be published?

I would like to do a follow-up on the importance of a Geiod developed from gravitational readings only. This is of particular importance to coastal areas.

Sincerely,
Stephen Estopinal, PE, PLS
Baton Rouge, Louisiana

Additional articles on gravity will appear in our spring 2013 issues.
Shelly

The Fluid Nature of Our Non-simplistic Solar System

For the staff of Professional Surveyor Magazine,

This reply is instigated from the Problem 215 by Mr. Bloch in your Jan. 2011 publication, page 45. Mr. Bloch refers to the Earth as having a radius of 6,377 kilometers. The figure is short by 461.49075 km.
Earth’s radius is 3463.0 nautical miles. [Mr. Gilmore then provides exact figures for a conversion of nautical miles to kilometers.]

He is also in error as to the angle subtended from the Sun to the Earth’s center. It is actually 0˚32’00.4”.

Best regards,
George E. Gilmore
Enid, Oklahoma

Dear Mr. Gilmore,

Because the Earth is not perfectly spherical nor is it solid, there is no single value that can serve as its natural radius. Distances from points on the Earth to the center can range from 6,353km to 6,384km.

The mean radius of the Earth, based upon several models, is around 6,371km. Tectonic forces also can perturb these values because the Earth is dynamic with drifting continents.

The Earth-Sun distance in its elliptical dance changes over time, and also has no exact fixed value.

Dr. Benjamin Bloch

Who Set Those Markers?

Shelly,

This is who (probably) set the markers on the international border referred to in the “What We Do” article: www.internationalboundarycommission.org/index-eng.html

Jim Fleming, LS
Hagerstown, Maryland

It’s a Parody!

Gigglebytes: Mr. Fix It” by Earl Henderson, PLS, in the January issue was absolutely hilarious. As fine a parody as I have read in a long time. I have been trying for decades to convince young surveyors the importance of collecting physical evidence of corner locations, including community acceptance, and the dangers introduced when re-setting corners by proportional measurement. The only certain thing about a proportional measurement is that it will not place the corner in its original location.

Then I began to wonder, what if some engineer doesn’t realize the work is a parody?

Please, pass my congratulations along to Mr. Henderson for an excellent story.

Sincerely,
Stephen Estopinal, PE, PLS
Baton Rouge, Louisiana

Gentlemen,

I had to write and tell you how much I enjoyed "Mr. Fix It" on page 28 of the January issue.  It hit pretty close to home!

Thank you, and Happy New Year!

Preston C. Haglin, PE
Fort Myers, Florida