Ruby gem geokit and :within maximum or tolerance?

Question

Just started playing with geokit and trying some things out...

Things are pretty much working as expected, given a point, its finding things nearby.

However, if I set :within to be a large value, say 100,000, using :miles, I would expect to get most (if not all) of the objects in the db returned - but it seems to stop at a certain point - as if there is a built in maximum for :within.

I have tried the formulas :flat and :sphere.

Thanks in advance, Chris

Answer 1

Your problem doesn't appear to be a built in maximum for :within but the lack of a limit (and sanity checking inside geokit).

It looks like a :within query ends up going through Geokit::Bounds.from_point_and_radius to produce a bounding box. from_point_and_radius will do a bit of trigonometry (see endpoint in mappable.rb) and the result will be an Geokit::Bounds instance.

I suspect that things are going wrong for you in the trigonometry; trig functions are periodic so your 100 000 radius will end up wrapping around to something between 0 and ~40 000 km (the Earth's circumference, ~25 000 miles) and the bounding box will not bound 100 000 miles. If you play with your 100 000 a bit you could probably get geokit to produce a bounding box that is only a couple centimeters per side (or a zero radius if you can sort out the usual floating point issues).

Executive summary: if you want them all, don't use :within at all; if you want to use :within, then give it a sensible distance (i.e. small enough to fit on the planet's surface without wrap around).