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Comment by hdersch | Hacker News Reader

"Viewsheds" of any location can be calculated and matched with photographs using "GeoImageViewer", an application I wrote a couple of years ago. Any feature in the image can be interactively identified in a mapview and vice versa, including the boundary of the viewshed. As has been mentioned in the comments, it is essential to include atmospheric refraction in the calculation, at least for distances above ~100km.

[1] https://hdersch.github.io/Viewing.html

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What a fantastic tool.

I'm the author of the post. Do you have any knowledge about how refraction can vary? I was wondering about calculating the world twice, once with a lower refraction bound and then again with an upper.

Atmospheric refraction is due to the vertical gradients of atmospheric pressure, temperature, and composition of the atmosphere, all of which are usually not precisely known, and which vary with time, so one gets larger lines of sights at certain times. For my application I used the standard formulas for astronomical refraction (-> many weblinks) with constant medium gradients. If I recall correctly this results in ~100m height correction for features in 100km distance and ~400m in 200km distance (features appear higher than without atmospheric refraction). For your application it would make sense to use two extreme values for the gradients to get maximum and minimum, as you suggested.

Right, yes variance over time is what I was referring to. I did a bit of research and indeed there seems to be some evidence backed minimum and maximum values I can plug in. But it's quite a variance! Now I'm thinking I should do min, max and average.

There's also https://www.heywhatsthat.com/

This looks amazing! I recently moved to an apartment with a good view out the window, so I was excited to try this to identify some of the more distant hills I can see. Alas, it seems to have developed some bugs in the 4 years since the last commit… when I tried clicking in ‘Edit Mode’ to select a location, nothing happened and I couldn’t continue. Any chance you could look into updating this application?

Try https://www.peakfinder.com/ -- I use the Android app all the time (I have no memory of paying for it, though, maybe it used to be free?)

I’ve been using such tools already (in particular https://www.udeuschle.de/panoramas/makepanoramas_en.htm). But for smaller or more distant features, I’ve found it can be difficult to correlate their physical appearance with their appearance on the diagram. A calibration tool like hdersch’s would make this much easier!

Wow, this is really an incredible bit of work! Very impressive stuff, I look forward to using it!

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