geodistance

Calculates the distance on the surface of the earth.

Description

M-file to calculate the distance between two points on the earth surface, using different ellipsoid parameters.

• MATLAB release: MATLAB 5.2 (R10)

[John D'Errico]

Good help for the most part, but I don't see why the author forces the user to edit the code to choose a method, or even to know what the default method of 6 causes to code to do. IMHO, this is poor.

I do like that there is an H! line, but I was disapponted to see no error checking.

Also the author uses a massive if, else statement to set the ellipsoid parameters. This is silly, since a far better style of programming would define one 23x2 (or 2x23) array of numbers, and then index into it.

Whenever I see something like this that computes a distance, I'd expect to see a good definition of what are the units on distance. Does this return meters? Kilometers? Miles? Feet? Inches? Light years? What are the units?

Did the author do the computations in a good way? Just for kicks, try a few arbitrary test points. I would have though that a simple test would result in fairly consistent results. Sadly, no.

geodistance([0 0],[2 3])
ans =
   3.9946e+05

geodistance([0 0],[2 3],1)
ans =
       400.59

geodistance([0 0],[2 3],2)
ans =
       -400.5

So is the distance between these two points a negative number? Does the author know what units are returned? I think an author should test his own code before uploading it.

Too bad. When I first downloaded this code, I was hoping to be able to give it a higher rating. Having found those bugs, I'm now wondering if I was generous in this 2 rating. I'll happily return to this code if these problems are repaired.

[Tom Cunningham]

There's quite a bit of things you could do with a code like this with relatively little trouble, as John so ably pointed out. A GUI would be simple and helpful. Units identification is a must and could be educational (light-seconds, sound seconds), useful (miles, nautical miles, kilometers) and even humorous (furlongs, fathoms, leagues, spans, barleycorns, etc.

I haven't actually looked at the code, but the overall idea is appealing and has a lot of possibilities, if the author has the time. How about input in lat/long, or the GPS grid system, etc.? You could also output compass heading, etc.

Go for it, Mr. Rodriguez. Listen to John, he really knows his stuff.

[Orlando Rodríguez]

Thank you Tom, I guess there are additional interesting things than can be done with the code, although I do not know very much about GUI design. Nevertheless, I will keep your sugestions in mind.

[John D'Errico]

And now? Well done.

I also hope that one day in the future, the author will update this for units of barleycorns. (Just kidding there.)

[John]

Hello, I found a bug when running:
dist = geodistance([-1.8530 47.3080], [114.1000 22.1800]);
The program keeps running and would not stop. My version is 7.0.4.

[Orlando Rodríguez]

Hi John. In fact it doesn't converge, something that can happen with antipodal positions (which is not the case). I will check the code. Thanks for submitting the bug.

[Orlando Rodríguez]

Hi John. I found the bug: the function fails because of the atan function when calculating sigma. I changed it to atan2, and it fixed the problem. I will submit an update as soon as possible.

[Jonathan Sullivan]

Very well done.

Three suggestions:
1. You may want to consider vectorizing in order to speed it is needed to be called many times sequentially.
2. Perhaps changing the syntax to match MATLAB's distance function i.e. geodistance(lat1,lon1,lat2,lon2)
3. It would be nice if azimuth could be outputted as well. Perhaps checking nargout > 2, and then running MATLAB's azimuth routine, or one that you might have.

[Wallizada mohibullah]

Hi Orlando, i am trying to use this function, i have the mapping toolbox, but couldnt seem to find the function geodistance(lat1,lon1,lat2,lon2, actualradius ). If you have a copy of it, would it be possible to post or send it. Thanks

[Wallizada mohibullah]

please ignore the earlier post if you dont have it. thanks