CODEWITHSUNDEEP
databasepostgresqlgispostgis
DRMacIver
DRMacIver

Reputation: 2315

How do I convert a latitude/longitude pair into a PostGIS geography type?

I'm trying to load a bunch of latitude/longitude pairs into a PostGIS geography type so as to be able to query by location.

In particular I have a table with float latitude and longitude columns and a geography(Point, 4326) column. I would like to do

update mytable set geography = ???

The documentation appears to suggest that the following should work:

update mytable set geography = ST_GeogFromText('POINT(' || latitude || ' ' ||
                                                           longitude || ')');

It doesn't. I don't know what it's interpreting this point as meaning, but it only allows the longitude to lie between -90 and 90, so it's clearly not a longitude.

So, what do I do?

Upvotes: 35

Views: 29252

Answers (3)

Mike T
Mike T

Reputation: 43642

Here are some different ways to make geography types:

  • Convert numeric long and lat columns to a geog geography type:

     UPDATE mytable SET geog = ST_SetSRID(ST_MakePoint(long, lat), 4326)::geography

  • Convert a geom geometry column (SRID=4326) to a geog geography type using a simple cast:

     UPDATE mytable SET geog = geom::geography

  • Transform a projected geom geometry column to a geog geography type:

     UPDATE mytable SET geog = ST_Transform(geom, 4326)::geography

Note that the last two examples work on any geometry type. Also, the conversion from geometry to geography is often implicit, and these examples work without ::geography, however explicit casts are usually a good practice for these things.

Upvotes: 15

Dawid D
Dawid D

Reputation: 1151

To perform exchange between lat and lng you may use:

update mytable set geography = ST_GeographyFromText('SRID=4326;POINT(' || st_x(geom) || ' ' ||  st_y(geom) || ')');

with or without srid.

Upvotes: 5

DRMacIver
DRMacIver

Reputation: 2315

...sigh. Stupidity on my part. Apparently the correct order is longitude, latitude. I was fooled into thinking that both coordinates had the same range (-180 to 180) so thought something more subtle was going on.

Upvotes: 42

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