Question

I am trying to create random Lat/Lngs inside a bounding box. The below code creates Lat/Lngs and they plot on the map… and while they are in the right country, they are not in the right “box”

my bounding box looks like this:

top_left = 51.514881121099904, -0.1293877362387679 
bottom_right = 51.492151803709525, -0.09693947143827275

minLat = 51.514881121099904
maxLat = 51.492151803709525
minLng =  -0.09693947143827275
maxLng = -0.1293877362387679 

My code looks like this:

markers = []

10.times do
    x = minLat + rand(maxLat - minLat)
    y = minLng + rand(maxLng - minLng)
    latLng = [x,y]
    markers <<  latLng
end

markers.each do |x|
    puts "#{x[0]} , #{x[1]}"
end

But its not outputting the right lat/Lngs. Is there something I am doing wrong? Am I looking at this the wrong way?

For example one run outputs:

51.51778835694538 , 0.8479098023328967
51.56834519895925 , 0.70003581382595
52.47933844269927 , 0.6167209565236026
51.52116824209034 , 0.8997051592766233
52.26830135905681 , 0.7514635122980192
52.143607260212896 , 0.21838042686322268
52.04649651836466 , 0.6683244476203801
52.057410769358576 , -0.08734906181439461
52.053408170846915 , 0.1600069328435182
51.8991829618331 , 0.3993135670912452

But clearly 52.26830135905681 is not between the min and max lat… so I am a little confused

Does rand() do some sort or rounding up. Can it work on such large floats?

Answer 1

How is rand() defined? Can’t remember off the top of my head…

You can use ruby’s Random class (http://www.ruby-doc.org/core-1.9.3/Random.html) and do something like this:

rng = Random.new(seed)
lat = minLat + rng.rand * (maxLat - minLat)
lng = minLng + rng.rand * (maxLng - minLng)