Distances

phil/geo

The great-circle distance

Coordinates::distanceTo() is the haversine distance over a sphere of the Earth's mean radius, 6 371 008.8 m. It is within half a percent of the distance over the ellipsoid: enough to sort places and to show "2.7 km", not to survey.

$distance = $montreal->distanceTo($quebec);
$distance->meters;          // 233029.3
$distance->inKilometers();  // 233.03
$distance->inMiles();       // 144.8

Distance is zero meters or more, and finite; kilometers() and miles() build one, isShorterThan() and compare() order them.

Finding places near a point

A database finds places near a point in two steps: the bounding box narrows the search on an index, then the exact distance keeps those really within reach.

$box = BoundingBox::around($here, Distance::kilometers(10));
// WHERE latitude BETWEEN :south AND :north AND longitude BETWEEN :west AND :east
$near = array_filter($candidates, static fn (Store $store): bool => $store->position->distanceTo($here)->meters <= 10_000);

Near a pole, or when the box would cross the antimeridian, it takes every longitude: the query reads a wider band, and the exact distance still decides.