# Longest line of sight.

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04-19-2018 10:03 PM
New Contributor

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.

14 Replies
MVP Esteemed Contributor

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

this isn't a flatlander question is it

Esri Esteemed Contributor

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

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.

New Contributor

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.

Esri Esteemed Contributor

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).

New Contributor

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.

Esri Esteemed Contributor

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).

New Contributor

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?

MVP Esteemed Contributor

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

New Contributor

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.