Learning About Projections

[Pointdump]

I'd like to learn about Coordinate Systems. Here's a short list of concepts that I'd like to understand, and more important, how they relate to each other and how to deal with them in both field surveying situations and Civil 3D drawings in the office:

Ellipsoid
Geoid
Datum
Ellipsoid Height
Geoid Height
Orthometric Height
Plumb Line
Ellipsoid Normal
GRS80
NAD27
NAD83
WGS84
UTM
Clark 1866

In all my attempts to read more about these things, this is the kind of "writing" I find:

"These undulations represent the NIMA/GSFC WGS-84 EGM96 15' Geoid Height File. This file is a global grid of undulations generated from: (a) the EGM96 spherical harmonic coefficients and (b) correction terms that convert pseudo-height anomalies on the ellipsoid to geoid undulations."

Can anyone point me to a site or book that was not written by lawyers?

Dave

[ToddRogers-WPM]

We have several customers that are subsea surveyors.  They actually use a benchmark to set up on.  It's mainly done by sonar.  And yes, they have negative elevations.

[Pointdump]

Jay,

Thank you. I downloaded the big zip file on the the right of the page. I didn't see anything that looked like a PowerPoint file. Just drawings and some coord files.

I also went through Sinc's videos on the Quux site, and his Coordinate Transformations in Civil 3D article on the Edward-James site is exactly the sort of thing I'm looking for. His Working With Grid Coordinates PDF strangely isn't on the site any more.

This morning I stumbled upon Penn State's courses. I'm going to dive into that rabbit hole this morning.

Dave

[Pointdump]

Troma,

Maybe at the center of the earth, since your weight would be so great in all directions, you'd smash into the size of a marble. Or you'd get pulled in all directions. Or something.

As for dealing with negative elevations you can bet that someone would've complained by now if C3D couldn't handle them.

Dave