Post #1Help me with my math.
363' observation point.
1372' target.
16.2 mile distance.
What's the elevation angle -- to the nearest tenth of a degree -- above level (eye level) for a flat earth and for a globe earth (r=3959 miles); no refraction?
I got:
+0.7° for flat earth.
+0.6° for a globe earth.
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Post #20.1° may be too small an increment to measure with confidence using Theodolite app.
Despite a no-refraction 175' "drop" difference between a flat and globe earth over 16.2 miles, the angular delta may not be large enough to distinguish without more precise tools.
Could adding an 8-12x telephoto capability to the phone focal length help distinguish a vertical difference if 0.1°?
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Post #3I think enough eyes have seen this, so I'm going to assume there are no corrections to the geometry.
Here are the geographic details:
Observation Point: Cabrillo National Monument
32.674005, -117.238946Target Objective: Mount Helix Cross
32.767044, -116.983436Last week, I noticed I could see the cross on Mt. Helix from a San Diego bay overlook near where I work. I can't take photographs from there, but I can go out to the Cabrillo Monument; and so I played with Google Earth and did the math to try to predict what the elevation above eye the cross should be from that observation point at the end of Point Loma.
I'd hoped to make predictions first before taking a sighting to avoid after-the-fact calculations, which can sometimes be skewed to match what is observed to what one wants to see.
I'm going to work with the Theodolite app to calibrate it and see if I can repeatedly, consistently take measurements to within 0.1°. I've tried this taking level sightings at the Coronado Islands 20 miles away, but the elevation data on the islands is much less certain than the ground elevation of Mt. Helix summit.
I'm also going to see if a telephoto multiplier lens for a smart phone will enhance the sighting at all.
Prediction going in is the Helix cross will be elevated +0.7° if earth is flat. +0.6° if earth is a globe. Hoping I can do this in the mornings over the course of several days. I'll also thought it might be good to take some time lapse images for 15 minutes before and after each sighting to check for "Skunk Bay" -like dynamic atmospheric conditions.
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EDIT: Merged several posts to make OP adequate for upper fora.
~junker-------
Post #4Too much haze (smog) today for Theodolite/Phone camera, and I'm resigned to the fact that Theodolite app is just not up to the task. The cross hair line itself is 0.1° thick. And with needing to distinguish between 5.8° and 6.8°, getting level at 0.0° is critical. Even with repeated calibration, I felt the tool was inconsistent:
I was able to cut through the haze with my camera and, with a little color and clarity adjustment, was able to get a decent shot of Mt. Helix. (I'll
link to the original image file since it's large.)
Could analyze angles and elevations using the Hilton Bayside tower in the foreground as a gauge. Has to be better than Theodolite, which just isn't cut out for what I set out to do here.
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Post #5Cropped from original; resolution unchanged:
Can use this to figure vertical angle above level to Mt Helix summit (foot of the Helix cross). Need to find level first (different for FE and GE).
Photo taken from 363' elevation using a tripod set 4' high for a total of 367'
The Hilton, 26,739 feet away, is recorded as 385' tall on about 8' elevation (avg).
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Post #6Calculating elevation angles above horizontal level for both Mt. Helix and Viejas Mountain, based on the measurements of the San Diego Hilton Bayfront tower:
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Post #7Results recap:
The FE/GE "contest" starts to show more clearly with the unanticipated inclusion of Viejas. Helix measurements are too close to call and could easily be within margins of error.
I'll keep observing and measuring to see if different days/conditions produce different results; probably won't be able to bracket observations with time lapse imagery like I had hoped.
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Post #8Tried again today...same spot...earlier in the day this time, but more haze/smog trapped in the basin than yesterday.
Widened the field of view to capture Cuyamaca Peak and add that to measurement. GE (with standard 7/6 refraction) consistently undershoots while FE calculation overshoot increases with range.
Having to take photo with heavy color processing to create contrast due to haze. Lots of blue. But otherwise, unaltered.
Link to annotated photo in native 4000x2248 resolution is 2.2MB.