topic Re: Longest line of sight. in 3D Mapping Questions

Longest line of sight.

DonatasG_ — Fri, 20 Apr 2018 05:03:01 GMT

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.

Re: Longest line of sight.

DanPatterson_Retired — Fri, 20 Apr 2018 11:42:44 GMT

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

this isn't a flatlander question is it

Re: Longest line of sight.

XanderBakker — Fri, 20 Apr 2018 12:13:53 GMT

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.

Re: Longest line of sight.

DonatasG_ — Fri, 20 Apr 2018 12:14:08 GMT

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

Sure

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

Re: Longest line of sight.

DonatasG_ — Fri, 20 Apr 2018 12:23:47 GMT

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.

Re: Longest line of sight.

XanderBakker — Fri, 20 Apr 2018 13:36:03 GMT

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).

Re: Longest line of sight.

DonatasG_ — Mon, 23 Apr 2018 05:19:24 GMT

Xander Bakker wrote:
If only an observer height of 1m ... this would limit your site to 3.5 km.

This is correct. But we talk not about 1m above sea level - 1m above ground.

Finding a line of sight of 503 km would require a flat earth...

No.

For example both observers are on islands and standing on mountains 2km high. Distance between island is 200km. So we will have clear 200km line of sight.

At present moment most longest line of sight is ~538km. Mt. Dankova in Kyrgyzstan to Hindu Tagh in China.

I want to know is there exists technology to find out most longest line of sight.

Lines of sight | Beyond Horizons

Re: Longest line of sight.

XanderBakker — Mon, 23 Apr 2018 12:13:42 GMT

OK, so when you have two observers (2m height) both on mountains with an altitude of 2km, the maximum line of sight could be up to 320 km, assuming the earth is a perfect circle and there are no objects between the two observers, the maximum line of sight could be up to 320 km:

However, to determine the maximum theoretical line of sight, one should perform viewshed calculations or line of sight calculations between a set of mountain peaks. This is possible, but would require a DTM covering the world (have a look here: Free Satellite Data - TERRAINMAP Satellite Image Analysis ) and point locations of mountain peak and evaluate the line of sight between the points. This would probably require some scripting (or the use Model Builder).

Re: Longest line of sight.

DanPatterson_Retired — Mon, 23 Apr 2018 12:16:27 GMT

You also have to remember that the highest locations need to be surrounded by low elevations in order to see past them. So even if you were standing on top of the tallest mountain on earth, surrounding mountains, or even plateaus would obscure the ability to see a parcel of land further on.

Re: Longest line of sight.

DonatasG_ — Mon, 23 Apr 2018 12:36:01 GMT

Xander Bakker wrote:
should perform viewshed calculations

I know viewshed. But for calculation you need one known point (observer). In my case I do not have this information.

would require a DTM covering the world ... and point locations of mountain peak and evaluate the line of sight between the points. This would probably require some scripting (or the use Model Builder).

Scripting, etc. for me it will be too complex.

Do You think it is possible to find GIS Pro (paid help), who could give me answer?

Maybe it is too complex even for Pro and it takes years of calculations?

Re: Longest line of sight.

DonatasG_ — Mon, 23 Apr 2018 12:38:56 GMT

You are absolute correct.

Even Everest is not the point with longest line of sight

Re: Longest line of sight.

DanPatterson_Retired — Mon, 23 Apr 2018 12:41:04 GMT

Known points? begin with the shoreline of earth... find locations along the shoreline perimeter that look across from one another that are 320 km or closer together (ie Albania to Italy).

That would keep someone occupied for a long time... or drain your pockets of cash Perhaps a hobbyist

Re: Longest line of sight.

DonatasG_ — Mon, 23 Apr 2018 12:54:51 GMT

I got your point

It is even more complex, because it is not necessary 2 point divided by sea.

At present moment most longest line of sight is ~538km. Mt. Dankova in Kyrgyzstan to Hindu Tagh in China.

Re: Longest line of sight.

XanderBakker — Mon, 23 Apr 2018 13:06:48 GMT

You could use a DTM of the world and invert the heights (calculate max height - height) and use Sink—Help | ArcGIS Desktop to determine the sink locations (these will be the peaks). With those locations start the process of evaluating the lines of sight and see which one is the longest. This will take a considerable amount of processing capacity, but is feasible.

Re: Longest line of sight.

XanderBakker — Mon, 23 Apr 2018 13:21:08 GMT

BTW, I just stumbled upon this list of The Ultra-Prominences Page that contains a KMZ you can download and use as your locations. This is a list of "ultra prominence" peaks and could be a good start (based on SRTM):

Prominence is the relative elevation of a mountain summit. Prominence is the elevation difference between a summit and the highest point (saddle) that separates that summit from any higher summit.

Re: Longest line of sight.

mbevand — Wed, 06 Oct 2021 08:32:23 GMT

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!

Re: Longest line of sight.

mbevand — Mon, 25 Oct 2021 19:33:20 GMT

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 )