
Answer: How many center-pivot irrigation systems do you see? - rhema
http://searchresearch1.blogspot.com/2016/08/answer-how-many-center-pivot-irrigation.html
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LeoPanthera
I always wondered why these are laid out in a grid, and not hexagonally, which
is optimal for circle packing. You could fit more in that way.

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crikli
Good question.

That would be fairly (ok, wildly) impractical.

Most of the roads are gravel, which means that maintenance would be a
nightmare. Road graders aren't great at keeping the blade level on turns. So
you'd get buildup/digout at every turn.

When it rained you'd get run-off and erasion. Which makes me think of
drainage, wow, with the water making 120 degree turns roughly every half mile
you'd get some serious washout on those occasions when we get 2" dumped on us
in what feels like 10 minutes.

Zig-zagging across the country with a 24-row planter in tow would be a giant
pain in the ass (you plan your route minimize the number of turns you're
making). Would be a pain driving a combine fitted with a 12 row head. And at
harvest the trucks taking grain to the elevator or silos would be doing the
same zig-zagging.

It's not like the grain that's outside the obvious circle doesn't yield. It
get irrigated via runoff as well as powerful sprinkler guns at the end of the
pivot arm.

Credentials: grew up farming in central Nebraska, married into a 5th
generation farming family. Thousands of acres, all centrally irrigated via
pivot.

Edit: Didn't want opening tone to sound argumentative/condescending.

Edit 2: Just thought about power lines. They'd have to zig-zag too. Which
means the pole on the zag would have lateral force vectors acting on it, so it
would have to be reinforced/anchored. When the afore-mentioned washouts
happened, down goes pole and powerline.

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jamesrom
Your points are totally valid. But you wouldn't need to make sharp 120 turns.
You could just have very slight waves with a frequency of 1 mile.

[http://i.imgur.com/vJq0Q3i.png](http://i.imgur.com/vJq0Q3i.png)

Of course, driving on roads like these would be annoying.

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zeveb
> Of course, driving on roads like these would be annoying.

ITYM _awesome_. Those roads are normally 30 mph, so at with 1 mile fields one
would change course every two minutes

I wonder if it might help protect against highway hypnosis to have a course
adjustment every mile or so.

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abduhl
Kansas, and likely other mid-Western states that I don't know about, have
historically added "artificial" curves on their highways to increase safety by
stimulating drivers and reducing boredom.

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SmellTheGlove
Discussions like this are why I love this site. I've seen these from
airplanes, but never even thought about it enough to know it was called
center-pivot irrigation. Now I know how big they are, their density, why we
can't arrange them in a hex, etc.

Alright, so here's my question: Since we can't arrange the roads in a hex, why
not make the grid a little smaller or the irrigation arm a little longer so
that it can reach the corners of the grid. It would obviously run over the
road at the midpoint of each side, so if the road needs to stay dry-ish, shut
off the water supply automatically somehow at the ends of the arms. Then you
can make the whole square green. This creates an obstacle to watch out for
when using the road, but otherwise what am I thinking wrong here?

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Roritharr
Or just make the arm retractable.

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Noseshine
The more moving parts the more expensive, especially in maintenance. It's just
like harddrives in server farms, even small changes in drive reliability have
a big influence due to the number of them in operation in parallel.

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mcbits
I wonder what kind of interesting stats one could dig up from aerial images of
the farms near La Crosse, WI. Instead of a grid of circles, the farms carve
out a bunch of fascinating patterns in the fractal topography around the
river. (I'm sure there are similar layouts in other regions, but that's the
one that stands out in my memory.)

Example:
[https://www.google.com/maps/@43.6474645,-90.9363052,5382m/da...](https://www.google.com/maps/@43.6474645,-90.9363052,5382m/data=!3m1!1e3)

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folli
Any suggestions for open source tools doing this, e.g. in python or R?

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smitec
Here is one using open CV in python [1]. While there are many ways to find
circles the Hough transform is a fairly simple and popular one, I don't know
what Matlab uses internally but it would probably be an optimised version of
Hough for circles. you can see some more here [2], implementing this process
in raw python (with PIL or pillow) was something we did in our image
processing course in undergrad so certainly not out of reach if you wanted to
give it a go.

[1]: [http://opencv-python-
tutroals.readthedocs.io/en/latest/py_tu...](http://opencv-python-
tutroals.readthedocs.io/en/latest/py_tutorials/py_imgproc/py_houghcircles/py_houghcircles.html)
[2]:
[https://en.wikipedia.org/wiki/Circle_Hough_Transform](https://en.wikipedia.org/wiki/Circle_Hough_Transform)

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lscharen
I built a Machine Learning algorithm about a decade ago for doing this kind of
feature extraction. It was targeted for finding samples on a tissue
microarray, but it's basically the same problem (find approximately circular
features on an approximate grid).

The research was never published and it was a kind of a hack (an EM-style
algorithm that added a step to update grid parameters after the M-step of the
centroid fitting).

It worked well enough, but would not be able to handle the heterogeneous
circle sizes (1 mile + 1/2 mile) that are demonstrated in the post. Something
like this is so well constrained (1 or 2 circle sizes) that running a hand-
tuned mix of segmentation algorithms is a pretty good approach.

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visarga
How to count them with less effort - no need to count over the whole map.
Perhaps Google would ban you if they saw too many requests for map tiles.

So, here's how to do it: sample 100-200 locations in a country. In each
location, extract a tile of the map and count the circles in there. Then you
need to scale the sum by the total surface of the country divided by the total
surface of the sampled tiles.

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phreeza
The problem with that is that the locations of the sites are probably very
correlated, meaning that your samples will no longer be independent, and your
estimate would probably be biased.

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oli5679
If the sampling process gives you a random subset of tiles, I don't see how
the estimate could be biased. Even if you have a strange distribution of
circles (heavily clustered in certain geographies), the weak law of large
numbers would mean that the sample mean is an unbiased estimator for
population mean if your sampling process is iid (random number generation is
by definition iid).

[https://en.wikipedia.org/wiki/Law_of_large_numbers](https://en.wikipedia.org/wiki/Law_of_large_numbers)

I think you're confused between which restrictions apply to the sampling
process versus the underlying population.

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phreeza
Ugh, you are of course correct, I should not be allowed to comment on
statistics before having my first coffee. I think I had some diffuse ideas
about this not being a poisson processes in my head that lead me to this
faulty conclusion.

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aw3c2
One could probably improve the detection quality by using something like the
NDVI to separate vegetation from the background.

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kristianp
And here's the Question:
[http://searchresearch1.blogspot.com.au/2016/08/searchresearc...](http://searchresearch1.blogspot.com.au/2016/08/searchresearch-
challenge-8416-how-many.html)

