SYNOPSIS

<geo2code $lat $lon [$radius]>

DESCRIPTION**Note: geo2code is a deprecated function. Use the SQL
functions latlon2geocode() and latlon2geocodebox()
where possible instead.**

The `geo2code`

function encodes each latitude/longitude
coordinate given into one integer. This number can be indexed and
used with a special variant of Texis' `between`

operator for
bounded-box searches of a geographical region. The `$lat`

,
`$lon`

and optional `$radius`

parameters are integers in the
form $DDDMMSS$ (DMS "degrees minutes seconds" format), with negative
numbers representing south latitudes and east longitudes respectively
(note that longitude signs are the opposite of ISO 6709, which is
east-positive).

Valid values for `$lat`

are -90 to 90 degrees inclusive
(i.e. -900000 to 900000). Valid values for `$lon`

are -360 to 360
degrees inclusive. A `$lon`

value less than -180 degrees will
have 360 degrees added to it, and a `$lon`

value greater than 180
degrees will have 360 degrees subtracted from it. This allows
longitude values to continue to increase or decrease when crossing the
International Dateline, and thus avoid a non-linear "step function".
Passing invalid `$lat`

or `$lon`

values will return -1. These
changes were added in version 5.01.1193955804 20071101.

By using this encoding method and a special variant of the
`between`

operator, only one field need be indexed and searched,
instead of both latitude and longitude separately, which can be
time-consuming at search. The encoded position can be decoded back to
latitude/longitude with the `code2geo`

function
(here).

If the optional `$radius`

parameter is given, then a pair of
numbers is returned for each coordinate. The pair represents the
encoding for the NW and SE corners of a box that is twice the
`$radius`

in length on a side, with the given coordinate at the
center. The pair is returned as a comma-separated parenthetical
string. The result can thus be directly inserted into a SQL statement
to search the geographical region within `$radius`

$DDDMMSS$ of
the given coordinate (DMS "degrees minutes seconds" format). Where
available, the `latlon2geocodearea()`

SQL function is preferred
however, as it returns a true parameter, not SQL statement fragment.

DIAGNOSTICS`geo2code`

returns a `long`

integer for each
latitude/longitude coordinate pair given, for a `BETWEEN(aaa,
bbb)` GIS search. If a `$radius`

argument is given,
`geo2code`

returns a comma-separated parenthetical pair of
numbers instead, for the bounding box that contains a circle of that
radius centered on the point. All arguments are Texis/Vortex
$DDDMMSS$ integers (DMS "degrees minutes seconds" format,
west-positive).

EXAMPLE

In this example, latitude/longitude positions for cities were
encoded with `geo2code`

into the `GeoCode`

field of a table.
A `$latitude`

and `$longitude`

are passed to this function
(e.g. from a form) and used to search for cities in a boxed geographic
region centered on the given coordinate:

<A NAME=search> Cities within the region: <geo2code $latitude $longitude 20000> <!-- +/- 2 degrees --> <SQL "select Name from city where GeoCode between " $ret> $Name </SQL> </A>

CAVEATS

The `geo2code`

function was added in version 2.1.904800000 19980902.

The returned value in `$ret`

from `geo2code`

is
platform-dependent in format and accuracy; it should not be copied
across platforms. On 32-bit-`long`

platforms it is accurate to
32 seconds (about half a mile). On 64-bit-`long`

platforms it is
accurate to 1 second (about 100 feet or less).

The `between`

operator used here should have a regular (B-tree)
index on the encoded (left-side) field, and use the parenthetical syntax.
A search without parentheses (e.g. "`between $x and $y`

" loses
the special interpretation of the values and will not work correctly
with `geo2code`

values.

Note that the Texis SQL functions `latlon2geocode()`

etc.
default to east-positive longitudes, not west-positive as Vortex
`<geo2code>`

does.

SEE ALSO`<code2geo>`

Vortex function,
`latlon2geocode()`

, `latlong2geocodearea()`

SQL functions

Copyright © Thunderstone Software