Geodjango: PointField and GEOSGeometry

Question

If I can do this:

>>> from django.contrib.gis.geos import GEOSGeometry
>>> from django.contrib.gis.geos import Point
>>> point = GEOSGeometry('POINT(1 5)')
>>> print point
POINT (1.0000000000000000 5.0000000000000000)

Why can I not do this:

>>> lat = 1
>>> lon = 5
>>> point = GEOSGeometry('POINT(lat lon)')

GEOS_ERROR: ParseException: Expected number but encountered word: 'lat'
GEOSException: Error encountered checking Geometry returned from GEOS C function "GEOSWKTReader_read_r".

How can I use a variable to create a GEOSGeometry object?

LAT and LONG appear backwards according to gis stackexchange post http://gis.stackexchange.com/questions/11626/does-y-mean-latitude-and-x-mean-longitude-in-every-gis-software — dan gleebits, May 01 '15 at 20:33

score 19 · Answer 1 · answered Oct 20 '14 at 18:05

19

The accepted answer is incorrect. Points take the form of "POINT(longitude latitude)". You've reversed them.

answered Oct 20 '14 at 18:05

Shroud

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It took me some time to figure this out. I guess this should be mentioned in the documents. – Amin Alaee Jan 12 '17 at 11:46

score 8 · Accepted Answer · edited Oct 08 '19 at 05:21

8

You can surely do that, but with a slight modification

point = GEOSGeometry('POINT(%s %s)' % (lon, lat))

OR

point = GEOSGeometry('POINT(%d %d)' % (lon, lat))

When you do

`'POINT(lat lon)'`

you are not replacing the local variables lat and lon with their appropriate local variable values, and they are being evaluated literally. So, you would need to use substitution.

EDIT: Changed order of (lat, lon) to (lon, lat) to match the order GEOSGeometry is expecting. Although not explicitly stated in the documentation, it is evident from their examples.

edited Oct 08 '19 at 05:21

Evan

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answered Oct 03 '13 at 18:37

karthikr

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As mentioned in https://stackoverflow.com/a/26472089/1405577 the POINT should be POINT(longitude, latitude). Please correct this comment. – mjabadilla Jul 12 '18 at 22:57

Geodjango: PointField and GEOSGeometry

2 Answers2