@mkennedy?ÿ Indeed, I did type GRS80 when I meant to type NAD83(2011). Poor proofreading. I apologize for the confusion and thank you for being kind...

@frozennorth?ÿ NAD83 may be the rare one. Very helpful discussion, thank you.

@frozennorth?ÿ Yes, in math, it doesn't have to make sense.?ÿ But, what is/are the datum(s) used in WGS84?

@frozennorth?ÿ Let's take another example. Would you say that 36N, 80W does not exist on the GRS80 ellipsoid?

@jitterboogie?ÿ Not mine, dates back to the 1920s, maybe Punch magazine: There was a young lady named BrightWhose speed was far faster than light;Sh...

@rover83?ÿ I pretty much agree with you. When I wrote GRS80(1986) and GRS80(2011), I meant to write NAD(1986) and NAD(2011). The point I was trying t...

@jitterboogie?ÿ Now,J_B_, you know that space can be the Star Trek Version or the "don't violate my ..." version. That ECEF coordinate system is thre...

@mkennedy?ÿ It can be a difficult point. GRS80 has remained unchanged through all of the realizations of NAD83. What the various realizations of NAD8...

@frozennorth?ÿ Respectfully disagree. Note that HTDP shows that (0,0,0) on NAD83(2011) is not (0,0,0) on WGS84 G1674. Different realizations of WGS84...

@mkennedy?ÿ Look at Slide 13 here: Slide 1 (noaa.gov) Also, note here HTDP computations (noaa.gov)?ÿ that converting to WGS84 in HTDP is actually c...

@jitterboogie?ÿ I get it, but even sunrise isn't that simple. For about half the year, it's North of East and for the other half, it's South of East....

@jitterboogie?ÿ Not to put too fine a point on it, the ellipsoid is the model and ECEF is a coordinate system that allows calculations on the ellipso...

This paper by Rod Deakin tells us how. The formula on page 9 will do it, but it requires both cartesian and geographic coordinates. MERIDIAN DISTANCE...

I'm just an interested layman with no qualifications other than a math degree, but looking at the diagrams in the linked document below, it seems that...

Personally, I encourage observing NGS marks with whatever equipment you have. Visit the same mark on different days and see how the recreational GPS r...

@bill93?ÿ Sorta. If you look at the velocities on the HTDP output, North is negative, East is positive, and Up is negative. I interpret that to mean ...