"Sunlight Spire" LiDAR Elevation

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bdloftin77
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"Sunlight Spire" LiDAR Elevation

Post by bdloftin77 »

Summary:

Last night I took a look at Sunlight Spire's elevation based on The National Map LAS files. Its Geoid12B orthometric elevation (NAVD88) is 4265.98 m, or 13995.997 ft. The NGVD29 equivalent elevation (what you see on scanned USGS topo maps) equates to 4264.19 m, or 13990.135 ft. This makes sense, as in Colorado, the new NAVD88 elevations are several feet higher than the NGVD29 ones (eg. Mt Elbert: 14,433' vs 14,440'). The telemetric elevation you see on old USGS quads of 13,995' is 5' too high - it should be 13,990'. In 2022, based on latest models, I expect Sunlight Spire to be at around 4265.509 m (13994.452 ft) for model A, or 4265.545 m (13994.570 ft) for model B. Add 5 mm to these heights from the Geoid12B to Geoid18 conversion. (I explained further down what all this means).

LiDAR Data: https://apps.nationalmap.gov/downloader/#/
LiDAR Metadata - Reports Page: https://prd-tnm.s3.amazonaws.com/index. ... 8/reports/
(Use the detailed PDF named CO_Southwest_NRCS_2018_D18_Final_Project_Report.pdf for datum, geoid, and accuracy information) ^
Convert between Geoid12B/NAVD88 and NGVD29: https://geodesy.noaa.gov/NCAT/

Math, Geoids, and Ellipsoids:

When the new 2022 gravitational model comes out next year, we'll use the NAPGD2022 model, using Geoid2022. Approximate differences from the current vertical datums and this new model vary in the CONUS from ~0.2 m LESS in Florida to ~1.3 m LESS in Washington. In Colorado, the screenshot below shows an approximate -0.4 to -0.8 m difference. The mountains won't physically drop - we are defining a new uneven surface of equal gravity to approximate where sea level WOULD be across the whole earth. This is the definition of a geoid. Some locations have denser rock/magma beneath, causing a slight increase in gravity a set distance from the earth's center. Other areas are less dense below, having a slight decrease in gravity at that specified distance. As technology increases in accuracy, so do our approximations of how far from the center of the earth MSL (mean sea level) would be for any given location. This is why elevations vary depending on which vertical datum and geoid you use.

Link for map and addition datum change info: https://www.esri.com/about/newsroom/arc ... s-in-2022/
NAVD88 to NAPGD2022
NAVD88 to NAPGD2022
NAVD88_to_NGVD29.png (757.92 KiB) Viewed 2767 times
The earth is also approximated by an ellipsoid (squashed 3D oval shape). This is smooth and uniform, and most systems consistently use the GRS80 ellipsoid. To compare different geoids, we compare the geoid height at a given location. This can be positive or negative, depending on if the geoid (equipotential gravitational surface where the sea level would be) is above or below the ellipsoid. The orthometric height, or elevation above MSL, (what we call elevation) is determined by the screenshot and equation below. GPSs determine the HAE (height above the ellipsoid, or "h"). They use a geoid model (where sea level would be; in the US most companies use Geoid12B, which a good vertical basis for NAVD88) and math to determine the geoid height ("N"). Now that we know both how far above the ellipsoid we are, and how far above the ellipsoid mean sea level would be, we can finally calculate our orthometric height ("H"), or OUR elevation above that mean sea level model. Use the equation h = H + N.
Height Calculation
Height Calculation
HeightCalculation.png (143.17 KiB) Viewed 2767 times
To simplify things, let's pretend that we're standing right on the ellipsoid (ellipsoid height = 0). We can look up the geoid height relative to that ellipsoid at a certain location for several different geoids, then accordingly bump up or down our orthometric height. For Geoid12B, the geoid height is -15.528 m, or 15.528 meters below our ellipsoid. For Geoid18 (very close to Geoid12B - within a couple cm usually), our geoid height is -15.523 m: five millimeters higher. Now, we'll compare our Geoid18 height to the latest models, xGeoid20A and xGeoid20B. These are -15.928 m and -15.964 m respectively. This will bump Sunlight Spire's elevation DOWN by 0.471 m or 0.435 m (1.545 or 1.427 ft) respectively in 2022.

Find Geoid12B geoid height at a location: https://www.ngs.noaa.gov/GEOID/GEOID12B ... ation.html
Find Geoid18 geoid height at a location: https://www.ngs.noaa.gov/GEOID/GEOID18/computation.html

Crunching numbers: First solving for ellipsoid height to put into the conversion calculator.. 4265.98 + (-15.523) = 4250.457 = ellipsoid height. Throwing this and Sunlight Spire's coordinates into NOAA's calculation page, we get our results below.

In 2022, based on latest models, I expect Sunlight Spire to be at around 4265.509 m (13994.452 ft) for model A, or 4265.545 m (13994.570 ft) for model B. Add 5 mm to these heights from the Geoid12B to Geoid18 conversion.

New 2022 datums info: https://geodesy.noaa.gov/datums/newdatums/index.shtml
Geoid18 to xGeoid20 Conversion (Under What to Expect > xGeoid > xGeoid20 > Access Tool): https://beta.ngs.noaa.gov/GEOID/xGEOID2 ... tion.shtml
Geoid18 to xGeoid20
Geoid18 to xGeoid20
SunlightSpire_Geoid18_vs_xGeoid20A_B.png (161.98 KiB) Viewed 2767 times
Last edited by bdloftin77 on Thu Oct 28, 2021 11:41 am, edited 1 time in total.
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Re: "Sunlight Spire" LiDAR Elevation

Post by bdloftin77 »

Below are some screenshots from ArcMap, where I visualized the LidAR data. QGIS is good free GIS software that can also visualize LiDAR data, though I haven't used it for that purpose yet.
SS1
SS1
SS1.png (119.25 KiB) Viewed 2753 times
SS2
SS2
SS2.png (163.47 KiB) Viewed 2753 times
SS3
SS3
SS3.png (506.84 KiB) Viewed 2753 times
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Re: "Sunlight Spire" LiDAR Elevation

Post by bdloftin77 »

Below, I changed the symbology to better see the high point.
SS4
SS4
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Re: "Sunlight Spire" LiDAR Elevation

Post by HikerGuy »

5s5t70.jpg
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Re: "Sunlight Spire" LiDAR Elevation

Post by rijaca »

So what you're saying is that "Sunlight Spire" is not 14,000', is not officially named, and is not ranked.

It's status is less than Cameron. :mrgreen:
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Re: "Sunlight Spire" LiDAR Elevation

Post by goingup »

f**k, how do I un-climb that unworthy pile of s**t?
Last edited by goingup on Thu Oct 28, 2021 12:35 pm, edited 1 time in total.
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Re: "Sunlight Spire" LiDAR Elevation

Post by Monster5 »

I couldn't care less about the ranked/ unranked crap, but this process is super cool. Thanks for sharing.
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Re: "Sunlight Spire" LiDAR Elevation

Post by CheapCigarMan »

Just a feature on a ridge.
I should be on a mountain
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Re: "Sunlight Spire" LiDAR Elevation

Post by Salient »

I’ve seen videos of people climbing Sunlight Spire and it kinda looks like *ahem* male genitalia when you’re standing at the bottom. Has anyone who has been up there thought this or am I just dirty minded 😂
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Re: "Sunlight Spire" LiDAR Elevation

Post by yaktoleft13 »

Salient wrote: Thu Oct 28, 2021 11:35 am I’ve seen videos of people climbing Sunlight Spire and it kinda looks like *ahem* male genitalia when you’re standing at the bottom. Has anyone who has been up there thought this or am I just dirty minded 😂
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Re: "Sunlight Spire" LiDAR Elevation

Post by FireOnTheMountain »

Monster5 wrote: Thu Oct 28, 2021 11:27 amI couldn't care less about the ranked/ unranked crap, but this process is super cool. Thanks for sharing.
I just wanna know how this all plays into flat Earth :-k
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Re: "Sunlight Spire" LiDAR Elevation

Post by greenonion »

What does this mean for Sunshine Peak (next to Redcloud)? And Huron?
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