diff options
Diffstat (limited to 'db/schema.sql')
| -rw-r--r-- | db/schema.sql | 32 |
1 files changed, 24 insertions, 8 deletions
diff --git a/db/schema.sql b/db/schema.sql index 59aacce6e..ba5ce4121 100644 --- a/db/schema.sql +++ b/db/schema.sql @@ -196,25 +196,41 @@ create type problem_nearby_match as ( distance double precision -- km ); --- problem_find_nearby EASTING NORTHING DISTANCE --- Find problems within DISTANCE (km) of (EASTING, NORTHING). +-- problem_find_nearby LATITUDE LONGITUDE DISTANCE +-- Find locations within DISTANCE (km) of (LATITUDE, LONGITUDE). create function problem_find_nearby(double precision, double precision, double precision) returns setof problem_nearby_match as -- Write as SQL function so that we don't have to construct a temporary -- table or results set in memory. That means we can't check the values of -- the parameters, sadly. + -- Through sheer laziness, just use great-circle distance; that'll be off + -- by ~0.1%: + -- http://www.ga.gov.au/nmd/geodesy/datums/distance.jsp + -- We index locations on lat/lon so that we can select the locations which lie + -- within a wedge of side about 2 * DISTANCE. That cuts down substantially + -- on the amount of work we have to do. ' -- trunc due to inaccuracies in floating point arithmetic select problem.id, - sqrt(($1 - easting) ^ 2 - + ($2 - northing) ^ 2) - as distance + R_e() * acos(trunc( + (sin(radians($1)) * sin(radians(latitude)) + + cos(radians($1)) * cos(radians(latitude)) + * cos(radians($2 - longitude)))::numeric, 14) + ) as distance from problem where + longitude is not null and latitude is not null + and radians(latitude) > radians($1) - ($3 / R_e()) + and radians(latitude) < radians($1) + ($3 / R_e()) + and (abs(radians($1)) + ($3 / R_e()) > pi() / 2 -- case where search pt is near pole + or angle_between(radians(longitude), radians($2)) + < $3 / (R_e() * cos(radians($1 + $3 / R_e())))) -- ugly -- unable to use attribute name "distance" here, sadly - sqrt(($1 - easting) ^ 2 - + ($2 - northing) ^ 2) - < $3 * 1000 + and R_e() * acos(trunc( + (sin(radians($1)) * sin(radians(latitude)) + + cos(radians($1)) * cos(radians(latitude)) + * cos(radians($2 - longitude)))::numeric, 14) + ) < $3 order by distance desc ' language sql; -- should be "stable" rather than volatile per default? |