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Longest line of sight.

DonatasG_

As far I'm not familiar with GIS, my question can sound strange 🙂

Is it possible to calculate longest (theoretical) line of sight (in Earth)?

I found many tools which can calculate line of sight, but you must know at least point A, which in my case is unknown.

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mbevand

I'm happy to report that I finished a multi-threaded version of my program. I have been running it for about 1 hour and it already found a previously unknown(!) 510-km sightline:

Viewpoint location: 38.61475,75.18748 (China)

Bearing: 115.6°

Location of end point on horizon: 36.518409,80.331178

Length of sightline: 510.3 km

According to the list at https://web.archive.org/web/20190516221621/https://beyondhorizons.eu/lines-of-sight/ this makes my finding the 2nd longest sightline on the planet

I have decided to enlarge the scope of my search and to analyze 2.3 million viewpoints. This should take multiple weeks to run on a beefier PC.

I have confirmed the 510-km sightline using the udeuschle.de panorama generator (link: https://www.udeuschle.de/panoramas/panqueryfull.aspx?mode=newstandard&data=lon:75.18748$$$lat:38.61475$$$alt:auto$$$altcam:2$$$hialt:false$$$resolution:600$$$azimut:115.6$$$sweep:2$$$leftbound:114.6$$$rightbound:116.6$$$split:2$$$splitnr:1$$$tilt:-2.28333333333333$$$tiltsplit:false$$$elexagg:1$$$range:750$$$colorcoding:false$$$colorcodinglimit:493$$$title:2nd%20longest%20sightline$$$description:$$$email:$$$language:en$$$screenwidth:2560$$$screenheight:1414 )

Screenshot from 2021-10-25 10-09-30.png

mbevand

Hi @DonatasG_ it's 3 years later, but you may be pleased to know that I wrote a C program to do just what you wanted. I have 75GB of DEM data covering the whole planet (downloaded from http://www.viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm) and my program can automatically identify the best vantage points (peaks) and the longest sightlines. It takes into account the Earth curvature obviously, and also atmospheric refraction (configurable).

I just finished writing a first version today. It's not optimized yet (single-threaded) but it does correctly identify the exact same longest sightlines as the https://www.udeuschle.de/ panorama generator does when I spot checked it against a few peaks. In particular it does find the 538km sightline from Pik Dankova.

I am going to make the program multi-threaded in the next couple of days. It's not very hard. My performance modeling indicates it should take about 5-10 days of runtime on the PC I'm using (AMD 5 PRO Ryzen 4650G) to scan the whole Earth.

I may not monitor this thread, but you can get in touch with me by email m (at) zorinaq.com

Cheers!

XanderBakker

Interesting... If only an observer height of 1m is used in the formula shown below (according to this site: How far can you see on the open ocean? - Quora 😞

... this would limit your site to 3.5 km.

Finding a line of sight of 503 km would require a flat earth... or a ladder of about 10952 m high on top of the Mount Everest (8848 m).

DonatasG_

Xander Bakker wrote:
Can you elaborate a little more on your specific use case?

I want to find 2 most distance points with line of sight.

Both points should be ground level (or <1meter (for example)).

At this moment longest line of sight is ~503km.

I need to find out is longer line of sight exists and where these two points are located.

DonatasG_

"Earth's curvature of course and standing on the ground"

Sure

I'm not talking about flatland, even today is Friday

XanderBakker

These links might be interesting and involve exploratory analysis in ArcGIS Pro:

Exploratory analysis tools—ArcGIS Pro | ArcGIS Desktop

Interactive viewshed creation methods—ArcGIS Pro | ArcGIS Desktop

Can you elaborate a little more on your specific use case? If possible using an image to visualize what your after and/or explaining the data that you have and what you would like to obtain.

DanPatterson_Retired

accounting for Earth's curvature of course and standing on the ground obviously...

this isn't a flatlander question is it

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