Ever seen this error when using Graticule?
Numerical argument out of domain - acos
Similarly to the to_sql problem for some edge cases, Graticule::Distance::Spherical.distance (and possibly those of Graticule's other distance computation classes) is subject to Float rounding errors.
This can cause the above error, when the arc cosine of something slightly more than 1.0 is to be computed, e.g. for the (zero) distance between the same coordinates (applies only for some).
How to fix
So, similar to the SQL fix, we just force the value we compute the arc cosine of into [-1; 1] bounds.
Put this into a config/initializers/graticule_spherical_distance.rb initializer:
Graticule::Distance::Spherical.class_eval do
def self.distance(from, to, units = :miles)
from_longitude = from.longitude.to_radians
from_latitude = from.latitude.to_radians
to_longitude = to.longitude.to_radians
to_latitude = to.latitude.to_radians
input = [ [ (
Math.sin(from_latitude) *
Math.sin(to_latitude) +
Math.cos(from_latitude) *
Math.cos(to_latitude) *
Math.cos(to_longitude - from_longitude)
), -1 ].max, 1 ].min
Math.acos(input) * Graticule::Distance::EARTH_RADIUS[units.to_sym]
end
end
Spec
Here is a spec to add to your application:
describe Graticule::Distance::Spherical do
describe '.distance' do
it 'should work for edge case zero-distance computation' do
from = stub :latitude => BigDecimal('0.4991657542 5E2'), :longitude => BigDecimal('-0.1169188713 5E3')
to = stub :latitude => BigDecimal('0.4991657542 5E2'), :longitude => BigDecimal('-0.1169188713 5E3')
Graticule::Distance::Spherical.distance(from, to).should == 0
end
end
end
Posted by Arne Hartherz to makandra dev (2012-02-09 10:42)