mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-11-27 07:21:09 +08:00
128 lines
5.2 KiB
Plaintext
128 lines
5.2 KiB
Plaintext
This contrib package contains two different approaches to calculating
|
|
great circle distances on the surface of the Earth. The one described
|
|
first depends on the contrib/cube package (which MUST be installed before
|
|
earthdistance is installed). The second one is based on the point
|
|
datatype using latitude and longitude for the coordinates. The install
|
|
script makes the defined functions executable by anyone.
|
|
|
|
Make sure contrib/cube has been installed.
|
|
make
|
|
make install
|
|
make installcheck
|
|
|
|
To use these functions in a particular database as a postgres superuser do:
|
|
psql databasename < earthdistance.sql
|
|
|
|
-------------------------------------------
|
|
contrib/cube based Earth distance functions
|
|
Bruno Wolff III
|
|
September 2002
|
|
|
|
A spherical model of the Earth is used.
|
|
|
|
Data is stored in cubes that are points (both corners are the same) using 3
|
|
coordinates representing the distance from the center of the Earth.
|
|
|
|
The radius of the Earth is obtained from the earth() function. It is
|
|
given in meters. But by changing this one function you can change it
|
|
to use some other units or to use a different value of the radius
|
|
that you feel is more appropiate.
|
|
|
|
This package also has applications to astronomical databases as well.
|
|
Astronomers will probably want to change earth() to return a radius of
|
|
180/pi() so that distances are in degrees.
|
|
|
|
Functions are provided to allow for input in latitude and longitude (in
|
|
degrees), to allow for output of latitude and longitude, to calculate
|
|
the great circle distance between two points and to easily specify a
|
|
bounding box usable for index searches.
|
|
|
|
The functions are all 'sql' functions. If you want to make these functions
|
|
executable by other people you will also have to make the referenced
|
|
cube functions executable. cube(text), cube(float8), cube(cube,float8),
|
|
cube_distance(cube,cube), cube_ll_coord(cube,int) and
|
|
cube_enlarge(cube,float8,int) are used indirectly by the earth distance
|
|
functions. is_point(cube) and cube_dim(cube) are used in constraints for data
|
|
in domain earth. cube_ur_coord(cube,int) is used in the regression tests and
|
|
might be useful for looking at bounding box coordinates in user applications.
|
|
|
|
A domain of type cube named earth is defined.
|
|
There are constraints on it defined to make sure the cube is a point,
|
|
that it does not have more than 3 dimensions and that it is very near
|
|
the surface of a sphere centered about the origin with the radius of
|
|
the Earth.
|
|
|
|
The following functions are provided:
|
|
|
|
earth() - Returns the radius of the Earth in meters.
|
|
|
|
sec_to_gc(float8) - Converts the normal straight line (secant) distance between
|
|
between two points on the surface of the Earth to the great circle distance
|
|
between them.
|
|
|
|
gc_to_sec(float8) - Converts the great circle distance between two points
|
|
on the surface of the Earth to the normal straight line (secant) distance
|
|
between them.
|
|
|
|
ll_to_earth(float8, float8) - Returns the location of a point on the surface
|
|
of the Earth given its latitude (argument 1) and longitude (argument 2) in
|
|
degrees.
|
|
|
|
latitude(earth) - Returns the latitude in degrees of a point on the surface
|
|
of the Earth.
|
|
|
|
longitude(earth) - Returns the longitude in degrees of a point on the surface
|
|
of the Earth.
|
|
|
|
earth_distance(earth, earth) - Returns the great circle distance between
|
|
two points on the surface of the Earth.
|
|
|
|
earth_box(earth, float8) - Returns a box suitable for an indexed search using
|
|
the cube @ operator for points within a given great circle distance of a
|
|
location. Some points in this box are further than the specified great circle
|
|
distance from the location so a second check using earth_distance should be
|
|
made at the same time.
|
|
|
|
One advantage of using cube representation over a point using latitude and
|
|
longitude for coordinates, is that you don't have to worry about special
|
|
conditions at +/- 180 degrees of longitude or near the poles.
|
|
|
|
Below is the documentation for the Earth distance operator that works
|
|
with the point data type.
|
|
|
|
---------------------------------------------------------------------
|
|
|
|
I corrected a bug in the geo_distance code where two double constants
|
|
were declared as int. I also changed the distance function to use
|
|
the haversine formula which is more accurate for small distances.
|
|
Bruno Wolff
|
|
September 2002
|
|
|
|
---------------------------------------------------------------------
|
|
|
|
Date: Wed, 1 Apr 1998 15:19:32 -0600 (CST)
|
|
From: Hal Snyder <hal@vailsys.com>
|
|
To: vmehr@ctp.com
|
|
Subject: [QUESTIONS] Re: Spatial data, R-Trees
|
|
|
|
> From: Vivek Mehra <vmehr@ctp.com>
|
|
> Date: Wed, 1 Apr 1998 10:06:50 -0500
|
|
|
|
> Am just starting out with PostgreSQL and would like to learn more about
|
|
> the spatial data handling ablilities of postgreSQL - in terms of using
|
|
> R-tree indexes, user defined types, operators and functions.
|
|
>
|
|
> Would you be able to suggest where I could find some code and SQL to
|
|
> look at to create these?
|
|
|
|
Here's the setup for adding an operator '<@>' to give distance in
|
|
statute miles between two points on the Earth's surface. Coordinates
|
|
are in degrees. Points are taken as (longitude, latitude) and not vice
|
|
versa as longitude is closer to the intuitive idea of x-axis and
|
|
latitude to y-axis.
|
|
|
|
There's C source, Makefile for FreeBSD, and SQL for installing and
|
|
testing the function.
|
|
|
|
Let me know if anything looks fishy!
|