Wednesday, April 26, 2017

SearchResearch Challenge CONTINUED AGAIN! (Can you build an interactive widget for the island viewing problem?)

Since there's so much interest... 

... and since we seem to be making progress (see the comments in the last two posts), I'm going to continue this Challenge until next week.  My answer / analysis will be posted on Monday, May 1st.  

(We're so close.  Keep on trying!) 

Remember that the SearchResearch Challenge this week is to figure out how to make an interactive widget that can interactively show the relationship between height and visible distance in the "island viewing" problem.  That is:  

1.  Can you make an interactive widget that illustrates "how far out to sea can you see" without going into full-developer mode and writing a bunch of HTML, CSS, and Javascript?  

The comments from the last week have been pretty helpful, but nobody's got a solution yet.  It's possible that there isn't a good solution (that is, without going fully into HTML/Javascript), but we're tantalizingly close!  

Keep searching!  



I'm repeating the statement of what the widget should look like below... 

To get you started, here's a side-by-side sketch of what such a widget might look like.  In the first image, the observer's eye is 1.7 meters above the beach, which lets the observer see 4.7 km out to the visible horizon.  

The interaction is simple:  As you drag the red dot up, the value of the "height above the beach" changes.  In this image, it's 100m.  You can drag it down to 0, or up to a much higher number.   As you drag, the widget updates the "visible distance" number as you drag, and redraws the red line to touch a point on the circle (in this case, one that is 36 km out). 

In this next image, I've dragged it down a bit.  Here it's just 1.7 meters above the beach, and the red dotted line only goes out 4.7 km. As I drag the dot, the numbers should update, the line to the dot should move up and down, and the line to the point on the circumference of the circle should slide along to show the distance.  

NOTE:  These are sketches of what the widget might look like. They're NOT images from a working widget.  

The formula connecting these two variables look like this: 

     distance = 3.7 * (height ^ 0.5)  

where height is in meters, and distance is in kilometers.  (In the top example, since the height is 100m, the  square root of 100 is 10. Hence,  10 * 3.7 = 37 km.)  


  1. Geogebra is definitely the tool you're looking for - I know it from my work as a geometry teacher. Used Geometer's Sketchpad for a long time, then switched over to geogebra because it's free! Here's what I have so far.

  2. Geogebra is very cute. I was suspicious of Geogebra's calculations. Just now I went down the beach in front of my house and with my binos at 2m higher than the sea, I can easily see the shoreline of the island right in front of my house which is 11km away. Twice as far as Geogebra notes.

    I can offer ground truthing to anyone interested.

    jon tU

    1. jon tU, interesting topic – the variable gap between screen truth & ground truth… both can be affirming and/or misleading…
      while fun to play with and construct (or attempt to build in my case) I agree that the GeoGebra widgets are misleading, too many variables to plug in…
      but then remind myself that Dan asked for a widget, not necessarily an illustration of reality…
      this island… Bowen?
      roughly 8x the elevation of the Farallon islands… which are ~44 km off the mainland
      "The tallest mountain on Bowen Island is Mount Gardner with an elevation of 762m/2,500ft, while Mount Collins has an elevation of 411m/1,350ft."
      photographic evidence indicates a possible 50mile horizon from here,
      with the Farallones appearing well below the horizon from there (the Marin Headlands).

      this almost gives enough height…
      249 miles
      off topic - a memo from A future… via HvE
      … need a widget that shows how far we can see into the coming present… rain may be on tap for tomorrow.

    2. Hi Jon,
      Geogebra just compute the formula given by Dan ( 3.7*sqrt(h) — btw I think it should be 3.57 rather than 3.7 ) and nothing else. This formula gives the visible distance of altitude 0 meter, the shore for example. Anything above the shore will be visible from a farer place: the distance from which you can see an object (tree, hill, building, whatever) above the shore will be greater. That's why you can see the island (not the people sunbathing on the beach if any). Here's a Geogebra widget that illustrate that:

    3. am confused… tool - not location - specific…?
      have ocular widgetitis dystopian syndrome

    4. Hi remmij and all fellow searchers still there,
      No, the geogebra widget was not supposed to be precice, just meant to illustrate the phenomena. Here's a non-interactive graphic that tries to be clearer. When your eyes are 2m above the beach, the horizon is at 5,04 km (typo on the graphic), but on the islands 44 km from you, everything above 119 m (390 ft) is visible.
      (some (simplified) maths on wp:

    5. Je vous remercie - was curious about the "Passager clandestin" moniker…
      "Hence its famous paradox of the underground passenger: a rational actor has an interest in taking advantage of a collective action without participating in it."
      Passager clandestin (économie)

  3. Hi Dan,

    Here's a new version, still with Geogebra, that does exactly what you're asking for. I added a "Scale" cursor to modify the scale of the height above beach.

    I'm thinking of a new version where the curvature of the visible part of the "earth" changes according to the scale. If I've enough time…

  4. I don't have an answer for the challenge but thanks to it I found a wonderful tool that allows me to do a lot more than what is asked ("a lot more" according to my own needs). Ulrich Deuschle has created this amazing nameless tool that sketches panoramas given a viewpoint, a direction and an angle of view. That's where I confirmed that, under the ideal athmospheric circunstances, at least theoretically, you can see Mauna Loa (Hawaiʻi Island) from Kaʻala (Oʻahu Island):

    (This is my third attempt at publishing this comment. No idea why it isn't working on Chrome. I had to post it on Firefox.)

    1. A link to remember previous SRS Earth view, irrigation and New Google Earth

      Luis, how do you find the tool? Have you been able to find it searching, Remmij? I tried but no luck at the moment. Another question, Remmij, Do you know why Luis link is alive and not clickable? In my case I don't have option to open in new tab either. I need to Copy/paste

    2. nice BBC find Ramón – beautiful imagery/landscapes
      interesting that they state the Al Jouf site may have a 50 year reserve of water in the aquifer,
      not what I recall reading about the area when we were looking at center-pivot irrigation — would that make the BBC
      guilty of fake news & erroneous climate information?? or just sloppy copywriting… ¯\(°_°)/¯ –
      not sure about LMV's link… doesn't appear live to me… also had to c&p it - a German site, but offers Italian & English translation…
      Chrome offers Google translation of the initial link Luís provided… offers 3 options to create a panorama - I used the first map option to do my Farallon example.
      Generate a panorama

      a Muybridge image of Tower Hill - South Farallon Island (had the lighthouse on it)

      a little add'l info

      minus the light room
      Tower Hill

      Dan may have an unfair advantage in this challenge since it appears he has visited Tower Hill in the past…
      at least he is follow the safety protocols and wearing his hard hat… something he rarely has to do at Google…
      Dan explaining the nuances of search to a SE Farallon island Brown Pelican…
      A wonderful bird is the pelican
      His bill can hold more than his belican
      He can take in his beak
      Food enough for a week
      But I'm damned if I see how the helican

      Dixon Lanier Merritt

      breach - imgur is distracting

    3. Hi Remmij! Thanks for your comment. I like the Pelican and Whale photos. The links for the pelican are the same photo, just different caption from you. That was your intention?

    4. the Merritt/pelican limerick is all just one link… (if you right click, it all selects) sorry for the confusion.

    5. Hi Remmij, don't worry for the confusion. I thought you probably upload more that is why I asked. Thanks for telling us.

      About irrigation challenge, I didn't remember the details you did so searched [al jouf water supply 50 years] I know it has confirmation bias but even so, it helps

      From NASA:"...Although no one knows how much water lies beneath the desert—estimates range from 252 to 870 cubic kilometers—hydrologists believe it will only be economical to pump it for about 50 years..."

      Also, with new Google Earth is still possible to measure circles as Dr. Russell did on the Challenge? I think it should work. Sadly my lap doesn't haveenough power to run it and try it.

    6. This comment has been removed by the author.

    7. "...Although no one knows how much water lies beneath the desert—" sounds about right… think I was recalling these types of articles… grain production shutting down.
      shifting to import
      2015, grain/water
      Al Arabiya News


    8. Sorry for the long delay answering. I am not receiving alerts from your replies, no idea why.

      Ramón, I was lucky in the way I found Deuschle's panorama generator:

      a very dope Google search: [ what is the point on earth with the longest visibility ]
      2nd result: Longest lines of sight photographed....... : General - SummitPost
      from here followed a link to: Viewfinder Panoramas
      from here followed a link to: Ulrich Deuschle
      (broken link but forwarding to Deuschle's Nameless Panorama Generator

      I have been in a hurry so probably I haven't html'ed the link on my previous reply. I hope everything works fine on this one.

    9. Hello Luis! Thanks for sharing with us how you got the tool.

  5. Er… Apparently I just had forgotten to check the "Notify me" checkbox.