Author Topic: Global Navigation Satellite Systems -- tutorial (Read 27719 times)

St Ignatius · « **Reply #240 on:** October 01, 2017, 09:30:16 PM »

Quote from: Neil Obstat on October 01, 2017, 09:05:12 PM

I remember someone asking about elevations in this tutorial, and at the time I wasn't sure where they would be, but now that we're covering ellipsoids, this is the part to see for elevations.

Must have been your most studious student, Truth is Transitory....NOT!

It was your's truly... only one problem, I'm so lost right now, I'm going to have to start over completely with a fresh mind and try to make heads of tails of this tutorial. I thought I had a better understanding than what I actually have.

On a side note, I'm going to try to use this new file sharing option to supplement your earlier posts regarding earlier methods of radionavigation, so that I don't clutter your tutorial.

Neil Obstat · « **Reply #241 on:** October 01, 2017, 09:51:41 PM »

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Answer key for the Question inside the last page.
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Question: Position of summit of the Washington Monument?

Question
What is the latitude, longitude and ellipsoid height of the summit of the Washington Monument given the coordinates of (1115287.503, -4844432.918, 3982867.096)? Use the NGS conversion tool (http://beta.ngs.noaa.gov/gtkweb/). Make sure to choose the option to convert to lat-long (second tab) and choose a projection for conversion as XYZ. (Choose the best answer.)

a) N38∘ 53’ 22.08257” W077∘02’06.86427” 149.172m
b) N38∘ 53’ 29.61745” W077∘02’06.86427” 173.36m
c) N38∘ 53’ 22.08257” W012∘57’ 53.13573” 149.172m

Option a is the correct term since the inputs are the coordinates in (X, Y, Z): X = 1115287.503, Y = -4844432.918, and Z = 3982867.096, and the outputs are the positions in latitude, longitude, and ellipsoid height in NAD 83. Make sure that your output is in NAD 83, not the antiquated NAD 27 (which especially affects the height).

Note:
You have to select NAD 83 from the drop-down menu for BOTH inputs and outputs. By "the summit of the Washington monument" they're talking about the ground level at the base, apparently, not the top of the monument itself. But I'm not sure!

Neil Obstat · « **Reply #242 on:** October 01, 2017, 10:00:18 PM »

Quote from: St Ignatius on October 01, 2017, 09:30:16 PM

Must have been your most studious student, Truth is Transitory....NOT!

It was your's truly... only one problem, I'm so lost right now, I'm going to have to start over completely with a fresh mind and try to make heads of tails of this tutorial. I thought I had a better understanding than what I actually have.

On a side note, I'm going to try to use this new file sharing option to supplement your earlier posts regarding earlier methods of radionavigation, so that I don't clutter your tutorial.

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You might prefer to go to the source website, and register for a free account and just work the tutorial there. With all these stupid interruptions it might be hard to follow the material, plus my inability to get all the images to show up doesn't help. Some of their mini videos are really good, like the one that shows how the ellipsoid works, unit 5.
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You may be able to jump right in at unit 5, but if you want to be sure of the basics, a quick review of the first 4 units would be good, too. It's mostly terminology. And don't let the math scare you because you don't really need to work through that to get a grasp of what's happening here.
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If you don't remember how to do a Taylor series, that's no biggie!! HAHAHAHA
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Neil Obstat · « **Reply #243 on:** October 01, 2017, 10:09:38 PM »

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They've got another mini video here that I can't post because it's Flash.
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5c. Expressing positions in an orthometric reference surface

The geoid is a reference surface that attempts to portray where global mean sea level would be if there were no land masses or ocean currents, and Earth were to stop spinning. Heights based on the geoid are called orthometric heights. To convert ellipsoid heights into orthometric heights, we’ll need to use a geoid height model.

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(Here is the mini-video! Fortunately, they provide the text if you want it!)

Click for video text
“Imagine for a moment if we were able to make the surface of Earth be an ocean, perfectly calm, with no tides, no currents, and no other forces acting on it except gravity. In this situation, the mean surface of the ocean is an equipotential surface. This particular surface has a special name: the geoid.
The geoid is defined everywhere on Earth, even over land areas, since gravity exists everywhere. This surface is extremely important to society for managing coastal and water resources since gravity explains so much about how water flows. So, when people colloquially say “height above sea level,” they are actually referring to their height above the geoid.”

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---I uploaded this image, see below---[/font][/size]
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An orthometric height can be derived from a GPS-based ellipsoid height by subtracting the geoid height from the ellipsoid height. When post-processing your GPS data through OPUS, a geoid height model is used to convert the ellipsoid height to an orthometric height. Both ellipsoid and orthometric heights are provided. In addition, since geoid height models change over time, the OPUS report tells you which geoid height model was used to compute the orthometric heights.

The North American Vertical Datum of 1988[/font][/size]

Red lines indicate leveling lines and water level transfers originating from Pointe-au-Père, Rimouski, QC, Canada. These form the basis for the North American Vertical Datum of 1988, or NAVD 88.

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The official vertical datum of the United States of America is an orthometric datum known as the North American Vertical Datum of 1988, or NAVD 88. It is the result of precise geodetic leveling from a long-term tide station in Quebec, Canada throughout the North American continent. For more on vertical datums, see our Understanding Heights and Vertical Datums lesson.[/font][/size]

Example from OPUS solution provides coordinates in the North American Datum of 1983 (NAD 83), realization 2011, epoch 2010.0000. This naming convention precisely identifies which version of the NAD 83 reference frame was used. Similarly, the OPUS solution shows which Geoid height model was used to convert ellipsoid heights to their corresponding modeled orthometric height (e.g., GEOID12B).

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In the United States, ellipsoid heights within the National Spatial Reference System are currently based on the NAD 83 datum, which uses the Geodetic Reference System 1980 (or, GRS 80) ellipsoid. The NAD 83 datum also provides the official reference for horizontal coordinates in the U.S. Another reference frame and ellipsoid currently in use in the U.S. and elsewhere in the world is the World Geodetic System 1984 (or, WGS 84). Over time, ellipsoid datums have become more precise as better techniques for measuring points on Earth’s surface have become available.[/font][/size]

Since geoid models also improve with time (as we obtain more and better gravity data), GPS-derived orthometric heights will also increase in accuracy . These changes may only result in small, centimeter-level differences, but for high precision applications, this can be significant. To keep all GPS-derived coordinates (Φ,λ, h) consistent, it may be necessary to reprocess older GPS data using the latest GNSS software and geoid models.

For more information on vertical datums, see the Understanding Heights and Vertical Datums lesson.

Neil Obstat · « **Reply #244 on:** October 01, 2017, 10:13:38 PM »

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I have to apologize for how lousy this page is turning out. The source site looks much better.
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Since this material is so important to the thread, I recommend you go to the source site to get a better view of it. I don't know how to improve the looks of it here.
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The link right there at the end of the page takes you to a lesson that specializes in height.
"Skill level = 0" -- That looks like a great idea! This is the link address:
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https://www.meted.ucar.edu/training_module.php?id=1099#.WEdRmaIrLUI&ust=1492035478210000
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Tradplorable · « **Reply #245 on:** October 02, 2017, 08:09:00 AM »

Useless.

DZ PLEASE · « **Reply #246 on:** October 02, 2017, 08:20:11 AM »

Quote from: Tradplorable on October 02, 2017, 08:09:00 AM

Useless.

Hey, don't be so hard on yourself man.

Everyone is useful for something, often it is to feed plants, but that's pretty durned handy.

St Ignatius · « **Reply #247 on:** October 02, 2017, 09:31:39 AM »

Quote from: DZ PLEASE on October 02, 2017, 08:20:11 AM

Hey, don't be so hard on yourself man.

Everyone is useful for something, often it is to feed plants, but that's pretty durned handy.

Now that you mention it, I'm lacking in some good agricultural bi-products for my fall field tillage...

DZ PLEASE · « **Reply #248 on:** October 02, 2017, 09:39:16 AM »

Quote from: St Ignatius on October 02, 2017, 09:31:39 AM

Now that you mention it, I'm lacking in some good agricultural bi-products for my fall field tillage...

"Corn tastes a little weird; kinda has a flat, earthy flavor. What do you think?"

St Ignatius · « **Reply #249 on:** October 02, 2017, 09:50:45 AM »

Quote from: DZ PLEASE on October 02, 2017, 09:39:16 AM

"Corn tastes a little weird; kinda has a flat, earthy flavor. What do you think?"

That's hilarious... that's what I think!

Neil Obstat · « **Reply #250 on:** October 02, 2017, 10:32:46 PM »

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They don't explain the reason but it could have been ground water removal.
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30 feet in 50 years
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Neil Obstat · « **Reply #251 on:** October 02, 2017, 10:40:37 PM »

Quote from: St Ignatius on October 02, 2017, 09:31:39 AM

Now that you mention it, I'm lacking in some good agricultural bi-products for my fall field tillage...

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That's what pumpkins are for!
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St Ignatius · « **Reply #252 on:** October 02, 2017, 11:41:08 PM »

Quote from: Neil Obstat on October 02, 2017, 10:40:37 PM

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That's what pumpkins are for!
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But what about my pumpkin pie and pumpkin bread? My favorite time of year...

DZ PLEASE · « **Reply #253 on:** October 02, 2017, 11:45:52 PM »

Quote from: St Ignatius on October 02, 2017, 11:41:08 PM

But what about my pumpkin pie and pumpkin bread? My favorite time of year...

Roasted pumpkin seeds... best part.

St Ignatius · « **Reply #254 on:** October 02, 2017, 11:51:16 PM »

Quote from: DZ PLEASE on October 02, 2017, 11:45:52 PM

Roasted pumpkin seeds... best part.

Wow! I forgot about those... used to have them as a kid. Gonna have to ask my wife to learn how to make those. Thanks for reminding me of this treat... :ready-to-eat:

Author Topic: Global Navigation Satellite Systems -- tutorial (Read 27719 times)

St Ignatius

Re: Global Navigation Satellite Systems -- tutorial

Neil Obstat

Re: Global Navigation Satellite Systems -- tutorial

Neil Obstat

Re: Global Navigation Satellite Systems -- tutorial

Neil Obstat

Re: Global Navigation Satellite Systems -- tutorial

Neil Obstat

Re: Global Navigation Satellite Systems -- tutorial

Tradplorable

Re: Global Navigation Satellite Systems -- tutorial

DZ PLEASE

Re: Global Navigation Satellite Systems -- tutorial

St Ignatius

Re: Global Navigation Satellite Systems -- tutorial

DZ PLEASE

Re: Global Navigation Satellite Systems -- tutorial

St Ignatius

Re: Global Navigation Satellite Systems -- tutorial

Neil Obstat

Re: Global Navigation Satellite Systems -- tutorial

Neil Obstat

Re: Global Navigation Satellite Systems -- tutorial

St Ignatius

Re: Global Navigation Satellite Systems -- tutorial

DZ PLEASE

Re: Global Navigation Satellite Systems -- tutorial

St Ignatius

Re: Global Navigation Satellite Systems -- tutorial