Re: Geographic coordinate values format conversion to DD (Decimal Degrees) format

[Paul Ramsey <pramsey@xxxxxxxxxxxxxxxxx>]

On Dec 4, 2018, at 12:36 PM, Allan Kamau <kamauallan@xxxxxxxxx> wrote:

Does PostgreSQL (more specifically PostGIS) have functions for these types of conversions.

Below are examples of the geographic coordinates values I have coupled with the resulting decimal degrees values.
39.529053 N 107.772406 W=    39.5290530°, -107.7724060°
27.485973 S 153.190699 E=    -27.4859730°, 153.1906990°
30°32’39” N, 91°07’36” E=    30.5441667°, 091.1266667°
27.485973 S 153.190699 E=    -27.4859730°, 153.1906990°
1¡20'1N 103¡45'15E=    01.3336111°, 103.7541667°

SELECT st_astext(txt2geometry('S 20 10.8035165 W 176 36.074496'));

=    -20.1800586°, -176.6012416°

The "°" sign in the results is optional.

Nope, you’ve got a big ugly pattern matching problem there, unfortunately, and probably are going to have to regex your way out of the bag. PostGIS will help you output forms like that, but it doesn’t have any general handling of arbitrary DMS strings.

http://postgis.net/docs/manual-2.5/ST_AsLatLonText.html

Here’s a PLPGSQL example that does half of your cases.

CREATE OR REPLACE FUNCTION txt2geometry(textcoord text)

RETURNS geometry AS 

$$

DECLARE 

textarr text[];

sep text;

lon float8;

lat float8;

BEGIN

textarr := regexp_matches(textcoord, '(\d+)(\D?)(\d{2})\D?([\d\.]+)\D? ([NS]),? (\d+)\D?(\d{2})\D?(\d+)\D? ([EW])');

sep := textarr[2];

RAISE NOTICE '%', textarr;

-- DD.DDDDDD

IF sep = '.' THEN

lat := int4(textarr[1]) + int4(textarr[3]) / 100.0 + float8(textarr[4]) / pow(10, length(textarr[4])) / 100;

lon := int4(textarr[6]) + int4(textarr[7]) / 100.0 + float8(textarr[8]) / pow(10, length(textarr[8])) / 100;

-- DD.MM'SS"

ELSE

lat := int4(textarr[1]) + int4(textarr[3]) / 60.0 + float8(textarr[4]) / pow(10, length(textarr[4])) / 36;

lon := int4(textarr[6]) + int4(textarr[7]) / 60.0 + float8(textarr[8]) / pow(10, length(textarr[8])) / 36;

END IF;

IF textarr[5] = 'S' THEN

lat := -1 * lat;

END IF;

IF textarr[9] = 'W' THEN

lon := -1 * lon;

END IF;

RETURN ST_SetSRID(ST_MakePoint(lon, lat), 4326);

END;

$$

LANGUAGE 'plpgsql' IMMUTABLE

COST 100;