[EMI_Guy]

To: Louis Foxwell That’s dubious! It’s an island...at what level below the ground do you think the water table is? 13 posted on ‎8‎/‎13‎/‎2019‎ ‎10‎:‎15‎:‎14‎ ‎AM by gr8eman (Only the mediocre are always at their best) [ Post Reply | Private Reply | To 6 | View Replies | Report Abuse] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TXnMA, here is a response on another thread to the presence of tunnels on LSJI obviously discounting their possible existence due to the extremely high water table because of the sea.

GE shows a "delta" of about 115' from the shoreline to the [tennis court] elevation. So...if this difference is fairly reliable, then there's plenty of room to play with tunnel construction before encountering any water table I would think.

I've been bragging here about how reliable GE elevation figures are in most cases. Well...this little dig I made is throwing me. At a point on the shoreline south of the tennis court where there appears to be breakers, I'm getting call-outs of around 40' above sea level. Wut? Breakers would generally indicate roughly "at sea level". Right?

Using the GE ruler and extending out to sea from shore, I don't hit "0 feet" until 250' from the apparent shoreline.

Q: how does or where does Google Earth benchmark its sea level (0 feet) elevation?

[buffaloguy]

40’ above sea level over water.

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I looked at maps at University of Texas for LSJI (1954-1955) and the perimeter of the island has not changed since then. It is probably an error which google needs to correct.

[TXnMA]

"I've been bragging here about how reliable GE elevation figures are in most cases. Well...this little dig I made is throwing me. At a point on the shoreline south of the tennis court where there appears to be breakers, I'm getting call-outs of around 40' above sea level."

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Questions I always ask at times like these (in order of importance for measurements & setting placemarks (coordinate accuracy):

Are you sure that...

1. you have Preferences/3D View/Elevation Exaggeration set to minimum (0.01)?

2. you have Preferences/3D View/High Quality Terrain set to "ON" (checked)?

3. you have all TILT zeroed out?

4. you are working at maximium zoom?

5. you have North set to "top"? (Click on the "N" at upper right...)

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BTW, I've been thinking: the XYZ data for that USGS benchmark on your local hill was probably incorporated directly into GE's DEM/DTM/DSM. When you're positioned exactly on it (at max zoom), your GE elevation & coordinates should match the USGs's elevation & coordinates.

You probably can use it to calibrate the accuracy of your positioning. (Off-position = off elevation...) Try putting the coordinates from the BM into GE's "Search" field; that should "drop" you right on the BM point in GE's Digital Model .

Set a "placemark" there & click "Snapshot current view". Then, double-clicking on the placemark name -- at any time -- should return you to that exact point on GE's digital model -- even with the placemark not displayed (un-checked)...

(NOTE: You'll notice that the BM Placemark appears to "move around" on different views. The placemark is "fixed to" GE's Digital Model; the apparent positioning errors are introduced when images from varying satellite viewpoints are "draped over" the DSM -- and don't quit "fit"...)

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1) Just create a simple 2-point "PATH" -- starting in the water and running thru the profile you want to measure.

2) SAVE it with whatever name you like.

3) Right or CTRL-click on the filename, and = on the pop-up menu, click, "Show Elevation Profile"

Now, you can move your cursor along the plot at bottom -- and... Voilá!! '-)

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Notice that I was interested in the Tennis Court. Putting my cursor on the highest point on the profile puts it smack dab in the middle of the tennis court! Since this is a plot of the DEM/DTM/DSM, it definitely validates my "Warped Tennis Court" theory! (GE still thinks the middle of the TC is a sharp peak!)

Hope this was helpful!

TXnMA
  

P.S. EMI-Guy: hope you didn't mind my sharing this with others...

P.P.S. Other addressees: Hope this "NUts'N'Bolts" stuff didn't bore you! At least, it should give you confidence that we're not just guessing about this OHI analysis stuff! Besides -- some of you might want to help -- and here are some [unclassified] "tools of the trade"...'-)

WWG1WGA