> So the r of the curvature as used in EF is not the same as the point of origin in ECEF as I always assumed for some stupid reason.
i don't know that
i am also making presumptions. nothing directed to you. i am currently comparing the benefits of either LDP or GSDM vs state grid.
my opinion is it's time to make a change to either LDP or GSDM. how bout you, what's your opinion?
I took nothing you wrote personally. LDP r Us.
good to see that
seems to me like the LDP is a fitting application for county to state size projections/reference frames and a GSDM would be the choice for regional and beyond.
i'm still wrapping my head around all of it.
There's a decent illustration on a PSU website. I find that it's easier to explain the prime vertical or transverse radius of curvature. For a given point, drop a plane that includes the normal to the surface and is perpendicular to the plane that includes the meridian. The normal is also used to construct a geodetic latitude, which may make it easier to picture. In a sphere or circle, that plane will include the center, but the flattening of the ellipsoid or ellipse means that the plane usually doesn't include the center.
The meridional radius of curvature--I don't have a geometrical feel for it beyond the fact that it measures the curvature of a meridian's ellipse at a particular point.
The wikipedia article on Earth's radius has a diagram showing the relationships.
Our university has developed a 3d printer. I'm thinking I need one right about now.
All;
I apologize for not keeping up and responding to posted inquiries.
I just returned from a 4-week 6,200 mile road trip that took me to Virginia where, among other events, I got a personal tour of Dave Ingram's T-4, and to Minneapolis where I got to hold our new granddaughter.
I should have been more careful about using the term "radius of curvature" in the article and appreciate the help of those who promptly clarified that radius of curvature and distance from the earth's center of mass are really two separate issues.
Replies near the end of the thread raise the issue of low distortion projections (LDP) and the global spatial data model (GSDM). While honoring the practices that brought us to where we are (map projections), I wholeheartedly agree that the "true experience" of using the GSDM provides a way for surveyors to use local distances and true directions while remaining connected to the big picture (the National Spatial Reference System - NSRS).
The GSDM is based on the assumption of a single origin for 3-D data and uses standard rules of solid geometry for computations. The result is a system that is easy to use - but it does require a new way of looking at current practices. That is not necessarily easy and many are reluctant to invest the effort needed to "do it easier."
The extent to which surveyors take the lead in making that transition for the benefit of the entire spatial data user community gives me a "warm fuzzy."
Earl F. Burkholder
http://www.globalcogo.com
