As computer programmer with an obsession with standards and references I really enjoyed this series. A personal GNSS example of mine is that I requested the firmware developers of GoPro action cameras enable a toggle between WGS84 ellipsoid height and what they called “orthometric height” (here called “The Geoid” at the 53:51 mark). Now one can at least for the HERO11 Black model use strict ellipsoid heights which is good for later reference.
Hey Dave, I’m a survey party chief who just discovered your lectures, wealth of knowledge. I would be interested to hear your take on international law regarding land surveying especially regarding boundary surveying. Specifically how it has changed with advances in the industry in technologies….
In the beginning of the lecture I started to wonder how significant or not is the Moon position in precise levelling. Do we need some corrections for that? As it causes tides, it distorts the equipotential surfaces and plumb lines... Locally it is probably insignificant but for the whole net of height monuments?
I'm a bit unclear on GNSS orthographic height. Is the final elevation number the straight line distance above the geoid model surface and normal to the surface of the ellipsoid? Or is it the distance of the curved path normal to equipotential planes, mathmatically the same as acheived with leveling regardless of gravitational uniformity? Or, is the system simplifying the math to use straight lines that are normal to the ellipsoid while the geoid model elevation is a simple constant used to emulate the curved-path-elevation acheived with leveling only at the benchmark location and elevation? Scenerio: If you start at a high elevation benchmark in an area with large gravitational change, so the equipotential planes are not evenly dense (aka not parallel), and you dig a deep well a few feet from the benchmark all the way to the true physical equipotential surface and take a measurement. Would the height measured at the true equipotential plane at the bottom of the well be some non-zero value because the geoid model was massaged to match the surface benchmark with only a simple constant? An analogous example is the pressure-altitude adjustment on airplane altimeters and the current pressure setting broadcast by on-airport weather stations. The altimeter setting being broadcast will achieve an altimeter reading equal to true airport elevation at touchdown on the runway, but the altimeter adjustment is only changing the Y intercept, not the slope of the relation between absolute pressure and altitude (The slope changes with temperature.). So outside of perfectly "standard" atmospheric conditions the altitude indicated will be inaccurate both above and below the weather station elevation. (A slope change of about 10% for each 20⁰c. Assuming a standard temperature lapse rate of 2.5⁰ per 1000 feet in clear air.)
David Doyle presentation is equivalent to reading a whole text book on intro to geodesy. Thank you Sir.
I agree with you Dave Doyle at 21:20 . Are amazing.
As computer programmer with an obsession with standards and references I really enjoyed this series.
A personal GNSS example of mine is that I requested the firmware developers of GoPro action cameras enable a toggle between WGS84 ellipsoid height and what they called “orthometric height” (here called “The Geoid” at the 53:51 mark).
Now one can at least for the HERO11 Black model use strict ellipsoid heights which is good for later reference.
Again, invaluable presentation. Thank you.
This is gold. Best lecture ever. Thank you so much.
Best online class in this pandemic times. Thank you so much.
Thank you Dave !!!
Hey Dave, I’m a survey party chief who just discovered your lectures, wealth of knowledge. I would be interested to hear your take on international law regarding land surveying especially regarding boundary surveying. Specifically how it has changed with advances in the industry in technologies….
In the beginning of the lecture I started to wonder how significant or not is the Moon position in precise levelling. Do we need some corrections for that? As it causes tides, it distorts the equipotential surfaces and plumb lines... Locally it is probably insignificant but for the whole net of height monuments?
I'm a bit unclear on GNSS orthographic height.
Is the final elevation number the straight line distance above the geoid model surface and normal to the surface of the ellipsoid?
Or is it the distance of the curved path normal to equipotential planes, mathmatically the same as acheived with leveling regardless of gravitational uniformity?
Or, is the system simplifying the math to use straight lines that are normal to the ellipsoid while the geoid model elevation is a simple constant used to emulate the curved-path-elevation acheived with leveling only at the benchmark location and elevation?
Scenerio: If you start at a high elevation benchmark in an area with large gravitational change, so the equipotential planes are not evenly dense (aka not parallel), and you dig a deep well a few feet from the benchmark all the way to the true physical equipotential surface and take a measurement. Would the height measured at the true equipotential plane at the bottom of the well be some non-zero value because the geoid model was massaged to match the surface benchmark with only a simple constant?
An analogous example is the pressure-altitude adjustment on airplane altimeters and the current pressure setting broadcast by on-airport weather stations. The altimeter setting being broadcast will achieve an altimeter reading equal to true airport elevation at touchdown on the runway, but the altimeter adjustment is only changing the Y intercept, not the slope of the relation between absolute pressure and altitude (The slope changes with temperature.).
So outside of perfectly "standard" atmospheric conditions the altitude indicated will be inaccurate both above and below the weather station elevation. (A slope change of about 10% for each 20⁰c. Assuming a standard temperature lapse rate of 2.5⁰ per 1000 feet in clear air.)
is there a beginners lecture to understand the terminology?
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